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Mechanizing lettuce production. McLeod, Colin Dale 1973

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V 1 MECHANIZING LETTUCE PRODUCTION BY COLIN DALE McLEOD B.A.Sc. University of B r i t i s h Columbia 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of A g r i c u l t u r a l Engineering We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February, 197 3. In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department o f i V M / ' H J L V C J r^^pxy, ^ The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date \4-} ABSTRACT Economic analyses, which indicated a need f o r reducing lettuce production costs, were the basis for f e a s i -b i l i t y studies of mechanizing some production processes. These processes are the thinning and weeding operations. Thinning can be eliminated by p r e c i s i o n seeding while weeding can be reduced or eliminated by using a suitable mulch layer. Mechanization of these processes requires development of a mulch layer applying machine and a p r e c i s i o n seeder capable of seeding through the mulch. A model of the p r e c i s i o n seeder was designed, fabricated and tested. Test r e s u l t s were below the minimum acceptable performance l e v e l of the machine. Weaknesses i n the model were obvious and modifications are recommended. These modifications should bring the model to an acceptable performance l e v e l . A model of the mulch layer a p p l i e r was also designed and fabricated. F i e l d t e s t i n g was not completed, however, expected problems are discussed and al t e r n a t i v e s are recommended. The p r a c t i c a l f e a s i b i l i t y of both these machines cannot be completely evaluated u n t i l the models have been thoroughly f i e l d tested. - i -A C K N O W L E D G E M E N T S T H E A D V I C E / G U I D A N C E A N D P A R T I C I P A T I O N OF T H E P R O J E C T S U P E R V I S O R D R , E . O . N Y B O R G / A S S I S T A N T P R O F E S S O R A G R I C U L T U R A L E N G I N E E R I N G D E P A R T M E N T / U . B . C . is A P P R E C I A -T E D . IN P A R T I C U L A R H E I S T H A N K E D F O R H I S P A R T I C I P A T I O N A S A C O - A U T H O R IN A P A P E R P R E S E N T E D T O T H E A N N U A L M E E T -ING A S A E IN C H A R L O T T E T O W N / P . E . I , / J U N E 1 9 7 2 . P A R T O F T H I S P A P E R I S I N C O R P O R A T E D D I R E C T L Y IN T H I S T H E S I S A S P R E L I M I N A R Y F E A S I B I L I T Y S T U D I E S . T H E W I L L I N G N E S S / E N T H U S I A S M A N D T H E A C T I V E P A R T I C I P A T I O N IN C O N S T R U C T I N G T H E M O D E L S B Y M R . N . F . JACKSON/ T E C H N I C I A N / A G R I C U L T U R A L E N G I N E E R I N G D E P A R T M E N T / U . B . C . H A S M A D E T H I S P R O G R E S S IN T H E S T U D Y P O S S I B L E . T H E S U G G E S T I O N S O F M R . A . R . M A U R E R , H O R T I C U L -T U R A L I S T / C D . A . R E S E A R C H S T A T I O N / A G A S S I Z / A N D M R . J . F . C O N R O Y / H O R T I C U L T U R A L i S T / B . C . D . A . / C L O V E R D A L E A R E A C K N O W L E D G E D . T H E A S S I S T A N C E O F M R S . E . S T E W A R T IN P R E P A R I N G THIS M A N U S C R I P T I S A P P R E C I A T E D A N D A C K N O W L E D G E D . - i i -TABLE, OF CONTENTS PAGE ACKNOWLEDGEMENTS i TABLE OF CONTENTS i i LIST OF FIGURES i v LIST OF TABLES v i 1 . GENERAL INTRODUCTION 1 1 . 1 Project F e a s i b i l i t y Study 1 2 . ECONOMIC AND THEORETICAL FEASIBILITY 3 2 . 1 Introduction 3 2 . 2 Labour D i s t r i b u t i o n 3 2 . 3 Material D i s t r i b u t i o n 5 2 . 4 Land Use 7 2 . 5 Discussion of Results 12 2 . 6 Proposed Mechanization Procedure 14 2 . 6 . 1 Phase I 11 2 . 6 . 2 Phase II 14 2 . 7 Detailed Description of Phase I 14 2 . 8 Estimated L e t t u c e Production Costs Afte r Incorporating P h a s e I 17 3 . DESIGN OF THE PRECISION SEEDER 21 3 . 1 The Seed Selection System 21 3 . 2 The Seed Transporting System 27 3 . 3 The Planting System 32 3 . 4 General Information 38 3 . 5 Test Results - Precis i o n Seeder 39 3 . 6 P r e c i s i o n Seeder Recommendations 48 - I l l -TABLE OF CONTENTS (Continued) 4. DESIGN OF THE MULCH LAYER APPLIER 4.1 S o i l Preparation Unit 4.2 The Mulch Layer Control System 4.3 Machine Operation 4.4 Anticipated Problems 5 . GENERAL CONCLUSIONS REFERENCES - i v -LIST OF FIGURES FIGURE NO. PAGE 1 Labour d i s t r i b u t i o n i n producing one acre of lettuce 4 2 E x i s t i n g cost to produce one acre of let t u c e 6 3 Material cost d i s t r i b u t i o n i n producing one acre of lettuce 8 4 Proposed and e x i s t i n g lettuce bed configurations 10 5 Land use 11 6 Estimated cost to produce one acre of lettuce using Phase I techniques 19 7 Model p r e c i s i o n seeder 22 8 Seed hopper 22 9 Hopper gate and a i r brush 22 10 Hopper vent holes 24 11 Seed s e l e c t i o n drum and related components 24 12 Removal seed o r i f i c e 26 13 Teflon control plate i n s e r t 26 14 Seed s e l e c t i o n drum - end view 26 15 Seed receiver 26 16 A i r flow regulator 28 17 D i s t r i b u t i o n tube 28 18 Probe receiver 28 19 Inside shaft a i r flow regulator 30 20 Probe receiver - top portion 30 21 Probe receiver - bottom portion 30 22 Sprong loaded valve 30 - V -LIST OF FIGURE (Continued) PAGE 23 Planting a i r flow regulator 33 24 Piston and c y l i n d e r 33 25 The probe 33 26 Planting system assembled 34 27 Inside shaft 34 28 Probe-piston coupling 34 29 Timing gears 34 30 Roller and side plates 5 8 31 S l i d e r 58 32 S l i d e r and o r i e n t a t i o n controls 60 33 Drive system 60 34 The complete mulch layer a p p l i e r 63 35 Rotation axis f o r tension r o l l e r 63 - VI -LIST OF TABLES TABLE I Test Results of Seed Selection Unit II Test Results of Seed Delivered by Probe III Results of Tension Tests on Newsprint Using the Instron Apparatus IV Results of Tension Tests on Newsprint Using the Instron Apparatus V Results of Str a i n Testing Newsprint Samples i n the Instron Apparatus VI Results of Str a i n Testing Newsprint Samples i n the Instron Apparatus 1. 1. GENERAL INTRODUCTION In an e f f o r t to overcome low p r o f i t margins, a g r i c u l t u r e , l i k e many i n d u s t r i e s , has increased production to increase p r o f i t s . The r e s u l t i s usually a lower unit p r o f i t , but more u n i t s , increasing the return. The net r e s u l t , however, i s often a surplus which lowers the product value. Marketing boards have been formed to l i m i t t h i s pro-duction but have not been too successful when the product can be imported. Surpluses and t h e i r r e s u l t i n g problems w i l l cause a s h i f t i n emphasis from the t r a d i t i o n a l increased volume production to e f f o r t s to d i r e c t l y lower unit produc-t i o n costs. This study investigates the f e a s i b i l i t y of lowering unit lettuce production costs i n the Cloverdale area of B r i t i s h Columbia. The thesis i s divided into three main sections. The f i r s t section determines the needs and l i m i t a t i o n s f o r mechanization of lettuce production within economic guidelines. The second section d e t a i l s the design, development and t e s t i n g of a p r e c i s i o n seeder, while the t h i r d section discusses the design and development of a mulch layer a p p l i e r . Development of these two machines were a d i r e c t r e s u l t of the economic f e a s i b i l i t y study. 1.1 Project F e a s i b i l i t y Study The f i r s t objective was to determine how lettuce production costs were d i s t r i b u t e d . The economic study by Dorling (1) on the costs of mid-season lettuce production 1 Numbers i n parenthesis r e f e r to the appended references. i n the Cloverdale area of B r i t i s h Columbia was used as a basi f o r the economic analysis. The information contained i n t h i s report was reorganized.to group associated production costs f o r a more physical presentation of work d i s t r i b u t i o n and according to each production phase. This enabled the analysis of separate production costs as part of a t o t a l system and determined where the largest expenditures occurred. The production phases r e s u l -t i n g i n largest expenditures were analysed i n d e t a i l to determine methods of cost reduction. The t o t a l production system i s a series of i n t e r -dependent operations where any change made i n one operation w i l l a f f e c t the remaining operations. It follows that a high cost operation occurring e a r l i e s t i n the t o t a l produc-t i o n system should be analysed f i r s t , followed by the next highest i n the t o t a l production sequence. 3. 2. ECONOMIC AND THEORETICAL FEASIBILITY 2.1 Introduction The report by Dorling (1) indicates a very low p r o f i t margin f o r lettuce growers i n the Cloverdale area. Any drop i n the price of lettuce due to competition or over supply could r e s u l t i n operating losses for the producers. S i m i l a r l y , any increase i n labour costs would eliminate the p r o f i t margin. An a r b i t r a r y increase i n the lettuce price i s d i f f i c u l t due to market competition. The only solution appears to be a reduction of operating costs. Labour costs are c e r t a i n to increase and as a r e s u l t , the labour intensive sections of lettuce production must be modified f i r s t . For the above reason, the study on mechanization of lettuce production i s divided into two phases. The f i r s t phase i s the mechanization of the labour intensive weeding and thinning operations.. The second phase i s the mechaniza-t i o n of labour intensive harvesting and packaging, and investigations into the high material costs associated with marketing. In the following discussion a l l costs reported are on a per-acre basis. 2.2 Labour D i s t r i b u t i o n An average of 39 3.1 man-hours i s required to produce one acre of lettuce using e x i s t i n g methods. This labour represents 44.1% of t o t a l production costs. The t o t a l costs may be divided among four general operations. Three of these operations involve d i s t i n c t inputs of labour and materials 4. 174.5 hours [S o i l Preparationj | Growing . . Harvesting . OPERATION FIGURE 1. Labour d i s t r i b u t i o n i n producing one acre of lettuce while the fourth i s made up of primarily f i x e d costs to which no d i r e c t operation can be charged. Figure 1 indicates the labour d i s t r i b u t i o n f o r one acre of land. This d i s t r i b u t i o n i s : Labour associated with s o i l preparation 13.0 hrs. Labour associated with growing 205.6 hrs. Labour associated with harvesting and d i s t r i b u t i o n 174.5 hrs.. TOTAL: 393.1 hrs. As can be seen, labour costs f o r s o i l preparation are n e g l i g i b l e while the labour involved i n growing and harvesting i s s i g n i f i c a n t enough to j u s t i f y a more det a i l e d analysis of these operations. Figure 2 presents a detailed breakdown of labour and material input f o r the three opera-t i o n s . A d e t a i l e d look at the growing operation shows that thinning and weeding account f o r 81.5% of the t o t a l labour and material cost of t h i s operation. The labour cost alone i s $305.21 per acre. Harvesting and packaging labour costs are $280.38 per acre accounting f o r 46.9% of the t o t a l cost of t h i s operation. Packaging materials represent 50% of the cost f o r harvesting and d i s t r i b u t i o n and account f o r 20.5.% of the t o t a l production costs, i n d i c a t i n g the need for further study i n t h i s area. 2.3 Material D i s t r i b u t i o n The average material cost f o r each acre of lettuce produced i s $444.46, representing 30.5% of the t o t a l production Labour Breakdown -5 Floating S Marking 6.44 — Discing 3.45-Ploughing 1. 89 -j Liming 3 .14 -j F e r t i l i z i n g 2.36 -j Manuring 3.14 H Sub Total Blocking 16.80 Thinning S hand weed-ing 232.36 Cu l t i v a t i n g (wheel hoe)46.63 C u l t i v a t i n g (basket weeder) 4.71 Big weeds (pul l i n g ) 4.71 Spraying 5.49 I r r i g a t i o n 9.42—j Seeding 2.67—T" OPERATION $1.57/hr 6. Material Breakdown 1. S o i l Preparation $20.42 $12.58 21.17 60.00 $ 114.17 $93. 75^~ J Sub T o t a l Cutting, Packing, Stapling Loading Hauling Making Cartons 262 .23 • 18.75 -18.15 -t 2, Production Operations S Maintenance. $322.79 | $51.71 $ 374.50 i 3 # Harvesting Packaging D i s t r i b u t i o n $10.72 21.45 15.33 4.21 -$299.00 Sub Total TOTAL COST $299.13 $299.00 $ 598.13 4 > Misc. Expenses Overhead $ 369.22 $ 1,456.02 Lime Manure F e r t i l i z e r Seed Seed Coating Spray Drainage Cartons S Staples FIGURE 2. E x i s t i n g cost to produce one acre of le t t u c e . cost. Figure 2 indicates the general d i s t r i b u t i o n of the material costs f o r the various operations, while Figure 3 d e t a i l s the material cost d i s t r i b u t i o n . As mentioned previously the purchase of packaging materials (staples and cartons) represents the largest single cost item f o r materials The packaging containers are therefore of some concern and a desired objective would be to replace the cartons with a less expensive container, preferably one that could be collapsed and recycled. Another aspect of the material costs (Figure 2) i s the cost of seed coating. Seed coating costs were approxi-mated as follows: The cost of uncoated lettuce seed i s approximately $6.00 per pound while coated seed s e l l s f o r $9.00 per pound. Since the a r t i f i c i a l seed coat weighs about twice as much as the i n d i v i d u a l seeds, one pound of coated seed consists of 2/3 l b . of coating material and 1/3 l b . of actual seed. On t h i s b a s i s , the seed cost of $32.17/ acre (Figure 2) i s composed of $21.45 for coating and $10.72 fo r seed. This figure becomes s i g n i f i c a n t i f the 525 acres growing lettuce i n the Lower Mainland area are seeded by p r e c i s i o n seeders requiring coated seeds. Seed coating would cost $11,261.00 per year. This seemingly i n s i g n i f i c a n t cost item alone indicates the value of a p r e c i s i o n seeder not r e q u i r i n g seed coating f o r operation. 2.4 Land Use An acre of lettuce produces an average of 733 cartons. On the basis of 24 heads per carton, t h i s represents 8. 300 250 — « 200 < •J o CO o o j l 5 0 < M w < 100 — 50 — FIGURE 3. Cartons [.Manure | ] F e r t i l i z e r ! L i m e 1 1 S p r a v l I s e e d 1 I Staples 1 SPECIFIC MATERIAL Material cost d i s t r i b u t i o n i n producing one acre of lettuce a y i e l d o f 1 7 , 5 9 2 h e a d s p e r a c r e . E a c h m a r k e t e d h e a d o f l e t t u c e t h e r e f o r e u t i l i z e s 2 . 4 8 s q u a r e f e e t o f f i e l d a r e a . O n t h e a s s u m p t i o n t h a t o n l y 50% o f t h e o r i g i n a l p l a n t s i n a f i e l d a r e a c t u a l l y m a r k e t e d , e a c h l e t t u c e p l a n t u t i l i z e s 1 . 2 4 s q u a r e f e e t o f f i e l d a r e a . A s s u m i n g a n a v e r a g e s i x i n c h h e a d d i a m e t e r , e a c h l e t t u c e p l a n t h o w e v e r o c c u p i e s o n l y 0 . 2 0 s q u a r e f e e t o f f i e l d a r e a . A t p r e s e n t , l e t t u c e i s p l a n t e d i n 48 i n c h w i d e b e d s . E a c h b e d c o n t a i n s f o u r r o w s o f l e t t u c e a n d i n d i v i d u a l b e d s a r e s p a c e d a t 14 i n c h e s . M o d i f y i n g t h i s s y s t e m ( F i g u r e 4 ) s o t h a t e a c h b e d c o n t a i n s s e v e n r o w s , w i t h i n d i v i d u a l p l a n t s s p a c e d a t 8 i n c h c e n t r e s , r e s u l t s i n t h e u t i l i z a t i o n o f o n l y 0 . 4 4 s q u a r e f e e t b y e a c h p l a n t . A n i n d i v i d u a l p l a n t w o u l d t h e r e f o r e u t i l i z e a f i e l d a r e a 2 . 2 6 t i m e s g r e a t e r t h a n t h e a r e a i t o c c u p i e s . ( F i g u r e 4 a l s o i l l u s t r a t e s a p r o p o s e d n e w s p r i n t m u l c h l a y e r , t o a c c o m m o d a t e t h e n e w r o w c o n f i g u r a -t i o n , w h i c h i s d i s c u s s e d l a t e r ) . T h e e f f e c t i v e l a n d u t i l i z a t i o n w i t h t h e m o d i f i e d p l a n t i n g c o n f i g u r a t i o n i s i l l u s t r a t e d w i t h t h e f o l l o w i n g e x a m p l e . F i g u r e 5 s h o w s a s q u a r e p l o t w i t h a o n e a c r e s u r f a c e a r e a . A l l o w i n g 10 f e e t w i d e h e a d l a n d s a t b o t h e n d s o f t h e b e d s , e f f e c t i v e r o w l e n g t h i s 1 8 8 . 7 f e e t . E a c h b e d a n d s p a c e b e t w e e n o c c u p i e s a 68 i n c h w i d t h , g i v i n g a t o t a l o f 36 b e d s p e r a c r e . T h e t o t a l e f f e c t i v e b e d l e n g t h i s 6 , 7 9 3 f e e t . A t 8 i n c h s p a c i n g t h e p o t e n t i a l n u m b e r o f l e t t u c e h e a d s i s 7 1 , 3 2 8 . I f , a s i n t h e p r e v i o u s e x a m p l e , o n l y 50% o f t h e 1 0 . PROPOSED CONFIGURATION INCLUDING MULCH LAYER Top View End View Mulch Layer Mulch Layer EXISTING CONFIGURATION Lettuce Bed Lettuce Bed J*8"_ J}8" e» | . © ® © & • • FIGURE 4. Proposed and e x i s t i n g lettuce bed configurations 10 t 208 1 Mulch l a y e r s c o n t a i n i n g l e t t u c e I 10 1 t 208 FIGURE 5. Land use heads are marketable and i t i s further assumed that y i e l d i s reduced an a d d i t i o n a l 15% due to closer planting, the r e s u l -tant increase i n production i s 142%. The above figures give a rough i n d i c a t i o n of the value of f i t t i n g new machines to the crop rather than spacing the crop to f i t e x i s t i n g machines. 2.5 Discussion of Results It i s noted that labour i s the largest single expense followed by material costs. A breakdown of the labour costs indicates that growing operations are the largest expense followed by harvesting and d i s t r i b u t i n g operations. The growing operations occur f i r s t i n chronological order and require the largest portion of labour. An analysis of labour d i s t r i b u t i o n indicates that thinning and weeding operations account f o r the largest portion of labour cost i n the growing operation. Thinning costs can be reduced by using e i t h e r an automatic thinning machine or a p r e c i s i o n seeder, while one of the easier ways to control weeds i s by the use of a mulch layer. The f i n a l decision to develop a mulch layer applier was made because mulch layers are a proven weed deterrant, they aid i n moisture conservation and they should r e s u l t i n increased y i e l d . With a l l the system components being interdependent, a thinning machine would be useless i f a mulch layer were applied and a mulch layer i s , i n turn, useless i f no machine i s available to plant seeds through i t . The decision to develop a mulch layer applying machine necessitates the need fo r a p r e c i s i o n seeder capable 13. of seeding through the mulch. Some thought was given to modifying a commercial seeder using coated seed, but a rough cost estimate of seed coating indicated that adapting a simpler p r e c i s i o n seeding technique might be more advisable. The p r i n c i p l e s used i n a p r e c i s i o n seeder developed at U.B.C. i n 1970-71 fo r containerized seedling production i n r e f o r e s t a t i o n have been thoroughly tested (2). This technique for s i n g l e seed s e l e c t i o n has proven i t s e l f s a t i s f a c t o r y f o r greenhouse seeding and i s considered suitable for seed s e l e c t i o n f o r p r e c i s i o n planting through a mulch layer. The seed s e l e c t i o n device does not require coated seeds. The only requirements i s that a seed be r e l a t i v e l y symmetrical about one axis. This symmetry need only be r e l a t i v e to the extent that i f one axis i s large compared to the other two then these two form e s s e n t i a l l y a symmetry about the long axis. Of course, true symmetry i r r e s p e c t i v e of r e l a t i v e axis length i s i d e a l . Thus the i n i t i a l study on the f e a s i -b i l i t y of reducing lettuce production costs becomes a f e a s i b i l i t y study of a combined mulch layer a p p l i e r and p r e c i s i o n seeding machine. Considering that some mulch e f f e c t s are known and that the seed se l e c t i o n concept i s e s s e n t i a l l y developed and tested, the problem reduces to designing a suitable p r e c i s i o n seeder and a mulch layer applier. Before designing these i n d e t a i l further f e a s i b i l i t y study i s required. This i s a com-parison between the estimated labour savings and the estimated increase i n m a t e r i a l s and equipment c o s t s . 2.6 Proposed Mechanization Procedure The proposed development f o r mechanizing l e t t u c e p r oduction may be d i v i d e d i n t o two d i s t i n c t phases. 2.6.1 Phase 1: The f i r s t phase i s the development of a mulch l a y i n g machine to place a cover over the s o i l to reduce weeding c o s t s . A modified v e r s i o n of an e x i s t i n g p r e c i s i o n seeder w i l l be i n c o r p o r a t e d i n t h i s machine t o e l i m i n a t e t h i n n i n g costs and seed c o a t i n g c o s t s . M o d i f i c a t i o n s i n c l u d e an a d d i t i o n a l device f o r seeding through the mulch and the use of a seed s e l e c t i o n nozzle s u i t a b l e f o r l e t t u c e . These proposed machines are d i s c u s s e d , i n some d e t a i l , below. T h e i r proposed design and f e a s i b i l i t y are discussed before e s t i m a t i n g t h e i r manufacturing and o p e r a t i n g costs.' 2.6.2 Phase I I : A f t e r completion of phase 1, development should be d i r e c t e d toward reducing the i n t e n s i v e labour costs i n the h a r v e s t i n g o p e r a t i o n . This may be accomplished by the design of a s u i t a b l e mechanical h a r v e s t e r . F i n a l l y , the m a t e r i a l costs f o r c o n t a i n e r s should be s t u d i e d and b e t t e r h a n d l i n g techniques should be recommended. The above order of development i s proposed because the l a r g e s t p o s s i b l e savings w i l l probably occur i n phase I . Completion of phase I should r e s u l t i n h i g h e r y i e l d s due t o more complete land u t i l i z a t i o n and w i l l r e s u l t i n savings due t o labour r e d u c t i o n . 2.7' D e t a i l e d D e s c r i p t i o n of Phase I Performance c h a r a c t e r i s t i c s of the o r i g i n a l seeder, 15. which are presented i n reference ( 2 ) , e s t a b l i s h the expected performance l i m i t s of the modified version when i t operates with the mulch laying machine. The control system on the mulch ap p l i e r i s the c r i t i c a l aspect of the machine. It i s p h y s i c a l l y impossible to remove paper mulch from a r o l l and place i t on the ground with zero stress remaining i n the paper. The reason f o r t h i s i s v a r i a t i o n i n the forward speed due to variable s l i p of the drive wheels on the prime mover. For instance, a paper r o l l drive mechanism driven d i r e c t l y from the t r a c t o r transmission w i l l place an excess of mulch on the ground i f t r a c t o r s l i p increases beyond the design value. S i m i l a r l y , i f s l i p decreases below the assumed value, the paper w i l l not be removed fast enough and the difference must be compensated fo r by s t r a i n i n the mulch paper. This s t r a i n w i l l be accompanied by corresponding stresses. A l l e v i a t i o n of the stresses w i l l occur through further s t r a i n (creep) and t h i s may r e s u l t i n a torn mulch layer. S i m i l a r l y , i f excess mulch i s applied, tearing may occur due to wind action. In order to overcome these problems a paper r o l l c o ntrol mechanism i s required. The control device must sense the mulch paper tension between the paper feed .. mechanism and the point of a p p l i c a t i o n . to- the. s o i l . .. Feedback ... from the control device i s sent to a variable speed unit to allow the paper to be applied to the s o i l surface at a uniform tension, independent of t r a c t o r drive wheel s l i p . As paper tension increases above a predetermined value, the paper discharge speed i s increased while a decrease i n paper tension r e s u l t s i n a decrease i n the speed of paper discharge. The variable speed unit should be capable of varying the speed of paper discharge i n a range of 0 to 100% of some selected base speed. The force required to activate the control system must not exceed the maximum allowable tension i n the mulch paper. It i s proposed that regular newsprint paper w i l l be used as the mulch layer f o r two reasons. Newsprint i s r e a d i l y available and i s economical. Secondly, a machine capable of placing a newsprint layer w i l l be s a t i s f a c t o r y fo r almost any other mulch material. The present r e t a i l p r i c e of newsprint i n Vancouver i s $165.00/ton. Considering a density of 50 lb/cubic foot, a 0.0025 inch thick layer 2 costs only 0.086<:/ft , while an 0. 003 inch thick layer costs 0.10^/ft 2. The newsprint applying machine must also be capable of l i m i t i n g stress conditions due to s o i l surface i r r e g u -l a r i t i e s . A r o l l e r and a s l i d e r , mounted i n front of and under the newsprint, r e s p e c t i v e l y , could be used to smooth out s o i l surface i r r e g u l a r i t i e s , preventing stress concen-. •. tpatiQns...in..the,, newsprint.-.. The,.slider,.would,not..,only, a s s i s t . . i n smoothing the s o i l but would also excavate the sides of the bed to allow the edges of the newsprint to be placed below the s o i l surface. The s l i d e r would also pack the 17. inside edges so that when the paper i s covered, compaction can occur with minimum displacement. This w i l l reduce stresses i n the mulch layer that w i l l be added when s o i l i s packed around the paper edges. This packing must be accomplished with minimum s o i l movement p a r a l l e l to the paper edges. 2.8 Estimated Lettuce Production Costs A f t e r Incorporating  Phase I The foregoing analysis has included the t h e o r e t i c a l f e a s i b i l i t y of phase I f o r reducing costs i n the thinning and weeding operations. The f i n a l determining c r i t e r i o n on which further expenditures of time and money depend i s the estimated maximum cost of using the new system based on no y i e l d increase. The following analysis w i l l not consider increased y i e l d but w i l l consider increased costs of seed r e s u l t i n g from seeding at the new spacings. The purchase of new equipment w i l l increase miscellaneous costs due to depreciation. In a r r i v i n g at the cost of the seeder and mulch layer , one-unit manufacturing i s assumed instead of assembly-line manufacturing. On t h i s basis the r e t a i l value of new equipment for phase I may be estimated as follows: Material per seeder head $ 25 .00 Labour and shop r e n t a l per seeder head 600 .00 Prototype- c o s f (-7 -heads) • - -•«f ,-3-75 .00 Material f o r mulch applier 100 .00 Labour and shop r e n t a l f o r mulch ap p l i e r 600 .00 Sub-total 5 ,075 .00 20% overhead and depreciation on manufacturing and d i s t r i b u t i o n 1 ,015 .00 Royalties 1 ,000 .00 Sub-total 7 ,090 .00 Development costs - 10% 709 .00 RETAIL PURCHASE PRICE: $ 7 ,799 .00 18. The o p e r a t i n g t i m e f o r t h e machine, based on a f i e l d c o n f i g u r a t i o n as shown i n F i g u r e 5, i s 2.86 h o u r s / a c r e , assuming a machine speed o f 1/2 m i l e / h o u r . The average a c t i v e t i m e f o r t h e s e e d e r on a 40 a c r e farm ( t h e average s i z e i n t h e s t u d y ) , seeded t h r e e t i m e s p e r y e a r i s 343.2 h r s . F o r a 2,000 hour machine l i f e , t h i s r e p r e s e n t s s e e d i n g 7 00 a c r e s . The d e p r e c i a t i o n , assuming no r e s a l e v a l u e would be $11.14/ a c r e . F o r a 1,000 hour l i f e , t h e d e p r e c i a t i o n c o s t s a r e $22.28/acre. F o r c a l c u l a t i o n o f t h e seed c o s t s due t o t h e new p l a n t i n g d e n s i t y , assume t h a t t h e e x i s t i n g p r o d u c t i o n o f 17,592 heads p e r a c r e r e p r e s e n t s 70% o f t h e seeds p l a n t e d . From F i g u r e 3 t h e s e c o s t $10.72. The seed c o s t f o r 71,328 heads would t h e r e f o r e be $3 0.42. F o r c a l c u l a t i o n o f t h e s e e d i n g l a b o u r assume 2.85 ho u r s o f p l a n t i n g and 2.15 hours f o r m i s c e l l a n e o u s a s s o c i a t e d a c t i v i t i e s . An average l a b o u r c o s t o f $1.57/hour, r e s u l t s i n a l a b o u r c o s t o f $7.85/acre. F i g u r e 6 shows an e s t i m a t e d c o s t c h a r t i n c o r p o r a t i n g a l l a s p e c t s o f phase I e x c e p t t h e c o s t o f t h e mulch paper . The d i f f e r e n c e i n c o s t s between F i g u r e s 3 and 6 i n d i c a t e t h e p o t e n t i a l s a v i n g s , n o t i n c l u d i n g t h e c o s t o f t h e mulch paper. The p o t e n t i a l s a v i n g s a r e $259.07/acre. I n o r d e r t o make a new t e c h n i q u e w o r t h w h i l e t h e p r o d u c e r s h o u l d g a i n a t l e a s t 50% o f t h e i n c r e a s e d s a v i n g s . T h e r e f o r e t h e maximum e x p e n d i t u r e f o r mulch s h o u l d be 2 $129 . 0 0 / a c r e , r e s t r i c t i n g t h e maximum mulch p r i c e t o 0.33£/ft . 19. Labour Breakdown -Sub t o t a l OPERATION $1.57/hr 1. S o i l Preparations $ 114.17 Weeding Seeding Spraying I r r i g a t i o n 20700 -7. 85 -5.94 H 9.42 • Sub t o t a l Production Operations $43.21 $49.96 $ 93.17 Material Breakdown NO CHANGE I— $30.42 Seed - 15.3 3 Spray 4.21 Drainage-Mulch costs not included-Sub Total 3, Harvesting Packaging D i s t r i b u t i o n V $ 598.13 NO CHANGE Addi t i o n a l Deprecia-t i o n 22.2 8 Sub Total 1 Misc. Expenses Overhead $ 381.22 1 $ 381.22 TOTAL COST $ 1,196.95 FIGURE 6. Estimated cost to produce one acre of lettuce using Phase I techniques. 20. For newsprint of 0.00 3 inch thickness, the price per acre at the e x i s t i n g r e t a i l p rice of $165.00/ton i s $30.70. This represents a cost of 0.10<7ft . Using news-p r i n t , the t o t a l production costs are estimated at $1,236.65/ acre. This represents an increase i n the return to management from $40.79/acre to $259.35/acre or an increase of 635.8%. The project appears economically and t h e o r e t i c a l l y f e a s i b l e warranting further i n v e s t i g a t i o n . The next stage i n the f e a s i b i l i t y study i s to design and b u i l d test models and study t h e i r p r a c t i c a l f e a s i b i l i t y . 3. DESIGN OF THE PRECISION SEEDER The p r e c i s i o n seeder i s b a s i c a l l y three separate mechanisms that operate together to take i n d i v i d u a l seeds from a seed mass and place them i n the ground. The f i r s t mechanism i s a seed s e l e c t i o n system, the second i s a seed transporting system and the t h i r d i s a seed planting system. A model seeder (Figure 7) which performs these functions, was designed, fabricated and tested. It i s discussed i n d e t a i l below. 3.1 The Seed Selection System B a s i c a l l y three separate functions are performed by the seed s e l e c t i o n system. These are: storing a mass of seeds, se l e c t i n g single seeds from the mass and metering i n d i v i d u a l seeds to the seed transportation system. The seed mass i s stored i n the seed hopper (Figure 8 ) . The hopper holds seeds i n a p o s i t i o n suitable f o r i n d i v i d u a l seed s e l e c t i o n . The hopper base angle i s greater than the angle of repose of the seed, allowing the seed to flow tov-ard the seed s e l e c t i o n drum (Figure 11) when the seed l e v e l i n the hopper drops. Two shafts (Figure 8-A) hold the hopper i n a fi x e d p o s i t i o n with respect to the seed s e l e c t i o n drum. An adjustable feedgate i s b u i l t on the hopper (Figure 9-A). Lowering the gate reduces the seed l e v e l at the seed s e l e c t i o n drum whereas r a i s i n g the gate increases the l e v e l . Once the gate i s fixed at a given height the seed l e v e l at the s e l e c t i o n unit remains constant, 22. FIGURE 8. Seed Hopper FIGURE 9. Hopper Gate and A i r Brush independent of the seed l e v e l i n the hopper. This independent condition e x i s t s u n t i l the seed l e v e l i n the hopper approaches the height of the bottom of the adjustable gate. An a i r brush i s mounted on the hopper (Figure 9-B). The only adjustment avail a b l e on t h i s model i s r o t a t i o n , which allows the p o s i t i o n of the centerline of the outflowing a i r to be adjusted. When the hopper i s placed i n a fixed p o s i t i o n the clearance between i t and the seed s e l e c t i o n drum i s 0.01 inches. The holes d r i l l e d i n the hopper (Figure 10-A) allow the a i r from the airbrush to flow out. Their r e l a t i v e size lowers the a i r v e l o c i t y to approximately 1/130 of the airbrush nozzle v e l o c i t y preventing the airstream from carrying seeds out of the hopper area. The second function, s e l e c t i n g single seeds, i s done p r i m a r i l y with the seed s e l e c t i o n drum and related components (Figure 11). The drum (Figure l l - A ) r o t a t e s . At one end of the drum i s the control p l a t e , a metal-backed t e f l o n i n s e r t (Figure 11-B) that f i t s into the end of the seed s e l e c t i o n drum. The control plate i s prevented from ro t a t i n g by a locking rod (Figure 11-C). The rod and con-t r o l plate are free to move p a r a l l e l to the axis of drum ro t a t i o n which allows the spring (Figure l l - D ) t o hold the control plate i n constant contact with the seed s e l e c t i o n drum. The seed s e l e c t i o n o r i f i c e (Figure 11-E) i s removable and screws into the drum u n t i l outside surfaces are f l u s h . (This removable seed o r i f i c e (Figure 12) i s incorporated FIGURE 10. Hopper Vent Holes FIGURE 11. Seed Selection Drum and Related Components i n t o the design t o make the model experimental. Should the seed s e l e c t i o n device appear f e a s i b l e , then t e s t s could be conducted f o r machine-seed performance f o r a l l h o r t i c u l t u r a l seeds by manufacturing and t e s t i n g v a r i o u s seed s e l e c t i o n o r i f i c e s , and using the one more s u i t a b l e f o r any s p e c i f i c seed type. The t e f l o n c o n t r o l p l a t e (Figure 13) i s i n contact w i t h the seed s e l e c t i o n drum. There are two main p a r t s on the c o n t r o l mechanism. There i s the vacuum groove (Figure 13-A) and the pressure hole (Figure 13-B). A p a r t i a l vacuum i s always maintained i n t h i s groove by connecting i t t o a vacuum pump. The f i n a l e n c l o s i n g surface f o r t h i s groove a l l o w i n g the p a r t i a l vacuum t o be maintained i s the drum c o n t a c t i n g surface (Figure 14-A). The pressure hole contains a i r pressure w i t h the same drum contact surface forming the f i n a l e n c l o s i n g s u r f a c e . This a i r pressure i s maintained above atmospheric pressure w i t h a pressure source connected to the h o l e . There i s a hole d r i l l e d p a r a l l e l to the drum c e n t e r l i n e (Figure 14-B) t h a t connects the contact surface w i t h the seed o r i f i c e socket on the drum. Thus, depending on whether the hole i s i n contact w i t h the vacuum groove or the pressure h o l e , a i r w i l l flow i n t o or out of the seed o r i f i c e . The t h i r d f u n c t i o n performed by the seed s e l e c t i o n system i s metering i n d i v i d u a l seeds t o the seed t r a n s p o r t a t i o n system. This i s performed by the seed r e c e i v e r (Figure 15-A). In a d d i t i o n t o r e c e i v i n g the seed discharged from the seed FIGURE 15. Seed Receiver o r i f i c e , the seed receiver d i r e c t s the seed into the a i r flow regulator (Figure 16-A). The seed s e l e c t i o n system works i n the following manner. The drum rotates, carrying the seed o r i f i c e through the layer of seeds held i n the hopper. At t h i s point the hole i n the drum contacts the vacuum groove and a i r flows through the seed o r i f i c e drawing seeds into the o r i f i c e . This a i r flow continues as the drum rotates carrying the seed o r i f i c e i n p o s i t i o n below the a i r brush. The p o s i t i o n of the a i r flow from the a i r brush nozzle i s adjustable and the a i r v e l o c i t y i s adjusted by increasing or decreasing the pressure. These two adjustments are varied u n t i l a l l but one of the seeds are blown away from the seed o r i f i c e back into the hopper. The seed o r i f i c e continues to rotate on the drum surface u n t i l i t i s above the receiver. The hole i n the drum i s now past the vacuum groove and i s aligned with the pressure hole i n the control plate. The a i r pressure d i f f e r e n t i a l i s therefore reversed at the seed o r i f i c e and outflowing a i r c a r r i e s the single seed away from the drum and into the rece i v e r , completing the cycle. 3.2 The Seed Transporting System The transporting system i s composed of the a i r flow regulator (Figure 16-A), the d i s t r i b u t i o n tube (Figure 17-A) and the probe receiver (Figure 18). The a i r flow regulator i s a simple r o t a t i n g valve composed of an outside c y l i n d e r and a r o t a t i n g center shaft. The seed receiver i s fastened FIGURE 17. D i s t r i b u t i o n Tube FIGURE 18. P r o b e R e c e i v e r to the top center of the outside c y l i n d e r , while the d i s t r i -bution tube connector (Figure 16-B) i s fastened to the bottom center. The centerlines of the connector and the receiver coincide forming a hole through the outside c y l i n d e r of the a i r flow regulator. This centerline bisects the cyl i n d e r axis at 90°. Another connector (Figure 16-C) connects a pressure supply to and through the wall of the cyli n d e r . The outside c y l i n d e r i s f i x e d i n p o s i t i o n . The inside shaft (Figure 19) rotates, driven by a gear timed with the seed s e l e c t i o n drum, ro t a t i n g at the same v e l o c i t y . There are two holes i n the shaft that are at 90° to and bi s e c t i n g the lo n g i t u d i n a l centerline of the shaft. One hole (Figure 19-A) passes through the shaft while the other i s at 90° to the through hole connecting i t with the shaft surface (Figure 19-B). There i s a s l o t (Figure 19-C) mi l l e d i n the rod p a r a l l e l to the shaft c e n t e r l i n e , that connects the pressure source (Figure 16-C) with the d i s t r i b u t i o n tube (Figure 17-A). Every c y c l e , when the s l o t contacts the pressure source, a i r flows through the s l o t , into the through hole and into the d i s t r i b u t i o n tube. The d i s t r i b u t i o n tube i s tygon tubing that conducts the seed from the a i r flow regulator to the probe receiver. The probe receiver (Figure 18) i s where the seed i s held u n t i l i t i s driven into the ground. There i s a connector (Figure 18-A) attaching the probe receiver to the d i s t r i b u -t i o n tube. The probe receiver i s composed of two sections, 30. FIGURE 19. Inside Shaft A i r Flow Regulator FIGURE 21. Probe Receiver -Bottom Portion FIGURE 22. Spring Loaded Valve a top p o r t i o n ( F i g u r e 20) and a bottom p o r t i o n ( F i g u r e 21). The top p o r t i o n has a c e n t e r h o l e a c t i n g as a probe guide ( F i g u r e 20-B) and s e v e r a l v e n t s . These vents a l l o w the a i r c a r r y i n g the seed t o exhaust, p r e v e n t i n g a b u i l d up of pr e s s u r e i n the t r a n s p o r t i n g system. T h i s p o r t i o n a l s o con-t a i n s a threaded screw ( F i g u r e 20-A) t h a t f i t s i n t o a s l o t on a probe and prevents the probe from r o t a t i n g about i t s own a x i s . The bottom p o r t i o n has a l a r g e i n s i d e diameter w i t h s l o p i n g w a l l s . The a i r stream goes out through the vent dropping the seed i n t o t h i s s l o p i n g r e c e i v e r . The seed s l i d e s down the s i d e i n t o another c e n t e r h o l e at the base t h a t serves as a second guide h o l e f o r the probe. There i s a s p r i n g loaded v a l v e c o v e r i n g t h i s second guide hole ( F i g u r e 22). In t h i s v a l v e , at the c e n t e r o f the second h o l e , i s a c o u n t e r s i n k where the seed i s s t o r e d u n t i l the probe c a r r i e s i t i n t o the ground. The t r a n s p o r t i n g system f u n c t i o n s as f o l l o w s . The seed drops i n t o the r e c e i v e r from the drum and g r a v i t y c a r r i e s i t down through the out e r c y l i n d e r o f the a i r flow r e g u l a t o r . I t r e s t s on the r o t a t i n g c e n t e r s h a f t . As the s h a f t r o t a t e s , the through h o l e l i n e s up with the c e n t e r l i n e of the d i s t r i b u t i o n tube and the seed f a l l s through the a i r f l o w r e g u l a t o r . The c e n t e r s h a f t c o n t i n u e s t o r o t a t e u n t i l the s l o t l i n e s up wit h the a i r p r e s s u r e source. At t h i s time a i r begins t o flow through the a i r f l o w v a l v e and d i s t r i b u t i o n tube, i n t o the probe r e c e i v e r . T h i s a i r s t r e a m c a r r i e s the seed i n t o the probe r e c e i v e r where the a i r f l o w and seed separate. The a i r flows at decreased v e l o c i t y out of the a i r vent and gravity c a r r i e s the seed to the bottom of the probe receiver, through the second guide hole into the countersink on the spring loaded valve. The seed has now been transported to a storage l o c a t i o n i n the planting system. 3.3 The Planting System The planting system i s divided into three main mechanisms, the planting a i r flow regulator (Figure 23), the piston and cylinder section (Figure 24), and the probe (Figure 25). The complete planting system (Figure 26) (excluding the planting a i r flow regulator) may be adjusted v e r t i c a l l y to vary the depth the probe goes into the s o i l (Figure 26-A). The cylinder and probe receiver are connected by a venting spacer (Figure 26-B). This venting spacer i s necessary to keep the cylinder and probe receiver aligned and the venting prevents piston and cylinder a i r leaks from i n t e r f e r i n g with seed p o s i t i o n i n the receiver. Four long bolts (Figure 26-C) hold these three units together and connects them to a pivot point. The pivot point (Figure 26-D) i s necessary because the seeder must move with respect to the s o i l surface and the pivot allows the probe t i p to, remain at one po s i t i o n i n the s o i l as the seeder moves. This allows the probe to enter the mulch and pivot to r e l i e v e the forces caused by r e l a t i v e motion that could tear i t . It should be noted that when a force i s applied to the probe ( i . e . force of entry into the s o i l ) the moment caused by F IGURE 2 3 . P l a n t i n g A i r F l o w R e g u l a t o r the r e s u l t i n g force about the pivot points tend to hold the planter v e r t i c a l . This prevents the seed planter from pivoting when the probe f i r s t enters the s o i l and the r e s u l t i n g force i s applied. The l i m i t i n g f a c t o r f o r the probe i s that i t must accelerate f a s t e r than l g regardless of. the acceleration d i r e c t i o n . This i s necessary to allow the seed to stay within the seed cup on the probe t i p as the probe t r a v e l s from the probe receiver to the s o i l surface. One complete probe cycle i s as follows: the probe extends, with accelera-t i o n greater than l g , through the probe rec e i v e r , capturing one seed with the probe cup. Extension with acceleration continues u n t i l the probe t i p has penetrated through the mulch layer and into the s o i l to the desired depth. The probe now withdraws back into the probe r e c e i v e r , leaving the seed i n the s o i l . The probe i s held i n the receiver f o r a suitable length of time to obtain the desired seed spacing i n the s o i l . I d e a l l y , considering the time f o r a complete machine cycle to be unity, the time i n the withdrawal p o s i t i o n should approach unity while the probe extended time should approach zero. As i d e a l conditions are approached the speed of forward t r a v e l can be increased with the speed then l i m i t e d by the transport system or peripheral drum speed l i m i t a t i o n s . The easiest apparent way to get a r a p i d l y extending and withdrawing probe appeared to be an a i r a c t i -vated piston, with flow controls designed to minimize the probe t r a v e l l i n g time and maximize the extended probe acceleration. This leaves the probe withdrawn for most of the cycle. Furthermore an a i r activated piston l i m i t s the force on the probe allowing an obstruction to stop the probe rather than cause mechanical damage that would occur i f a f i x e d displacement system were used. The f i r s t operating mechanism f o r the planting system i s the timing control. This c o n t r o l , c a l l e d the planting a i r flow regulator, i s a simple rotary valve. The rotary valve has.an outside c y l i n d e r (Figure 2 3) held i n a fix e d p o s i t i o n with an inside r o t a t i n g shaft on which a gear i s fastened (Figure 27). The outside cylinder has two through holes (Figure 2 3-A) complete with connectors. One hole forms a connector between an a i r pressure source and the piston top; the other i s a connector between an a i r pressure source and the piston bottom. There i s another set of holes , with one hole i n the plane of each through hole, that connects outside atmosphere with the inside of the outside cylinder. This set of two holes act as exhaust ports, one f o r the top of the piston and the other f o r the bottom. The gear on the r o t a t i n g shaft supplies the force to rotate the shaft and keeps the valve timed with the rest of the machine. There are two through holes on the ro t a t i n g shaft which a l i g n with the through holes i n the outside cy l i n d e r . There are also four s l o t s i n the same rotary plane of the shaft as the through holes. These s l o t s connect the top and bottom of the piston with t h e i r respective exhaust ports. These sets of sl o t s and holes are so positioned that when pressure i s applied to the top of the cylind e r the exhaust port for the bottom of the piston i s open. S i m i l a r l y , i f the pressure i s on the bottom of the piston the top exhaust port i s open. The piston and connecting rod are fabricated from one part to ensure that t h e i r centers were on the same axis to prevent binding, as both have small clearances to act as an a i r s e a l at the bottom as well as the top of the piston. . The piston t r a v e l and connecting rod length are determined by the maximum desired probe penetration. The probe and connecting rod are connected by a coupling (Figure 28) that allows the piston and connecting rod to rotate with respect to the probe whose rotary p o s i t i o n i s f i x e d . Relative l o n g i t u d i n a l motion i s prevented by t h i s coupling. The probe (Figure 25) has a s l o t milled down one side and the set screw i n the top part of the probe receiver f i t s i n t h i s s l o t to prevent the probe from r o t a t i n g . A t e f l o n t i p on the probe i s used to minimize d i r t and moisture adhesion. The t e f l o n t i p i s angled to gradually cut the mulch around the probe periphery, as the probe passes through.. The center of the t e f l o n t i p i s hollow to create a cup to hold the seed during s o i l entry to minimize seed crushing. The lead edge of the 3 8 . t e f l o n t i p s t r i k e s the spring loaded valve giving i t an acceleration greater than l g which, i n e f f e c t , leaves the seed suspended i n the centerline of the probe. This allows the seed to enter the cup i n the t e f l o n t i p of the probe as the probe i s accelerating f a s t e r than l g . R e l a t i v e l y , the seed f a l l s i n t o the cup. This mechanism operates i n the following manner. Aft e r the seed has landed i n the countersink of the spring loaded valve, the planting a i r flow regulator allows a i r to enter above.the piston and exhaust a i r below the piston. The piston, connecting rod and probe accelerate downward under the a i r pressure load. The probe s t r i k e s the valve and catches the seed i n the t e f l o n t i p . The probe containing the seed then enters the s o i l and reaches the f u l l t r a v e l . At t h i s point the planting a i r flow regulator introduces a i r below the piston while exhausting a i r above. This decelerates and then accelerates the probe, withdrawing i t and leaving the seed behind. When the probe has withdrawn s u f f i c i e n t l y , the spring loaded valve closes, completing one f u l l cycle of the seeder. In the meantime another seed has been selected and i s being transported to the probe receiver as part of' the next c y c l e . 3 . 4 General Information This experimental model has many variables i n c l u d -ing vacuum pressure, a i r brush pressure, seed discharge pressure, seed transport pressure and piston pressure. The seed o r i f i c e i s also variable and the depth of probe with the r e s u l t i n g seed penetration i n the s o i l i s adjustable. The a i r brush p o s i t i o n i s also adjustable. One adjustment that i s not available on t h i s model i s the probe cycle time. The time i n the cycle when the probe begins to extend and withdraw are constant. I f the pressures introduced are large, then the probe extends ra p i d l y to the f u l l y extended p o s i t i o n and w i l l not begin to withdraw u n t i l the planter a i r flow regulator reaches a pre-determined p o s i t i o n . This could leave the probe i n the f u l l y extended p o s i t i o n f o r too long. This i s a design f a u l t that should be corrected before actual f i e l d tests are i n i t i a t e d . The a c t i v a t o r to withdraw the probe must be a function of the probe p o s i t i o n only, while the probe extension that i n i t i a t e s the planting cycle must continue to be timed r e l a t i v e to the r e s t of the p r e c i s i o n seeder. Three gears (Figure 30) keep the machine parts synchronized. 3.5 Test Results - Precision Seeder A preliminary t e s t i n g experiment was conducted i n the laboratory to test the p r e c i s i o n seeder. The objective of the test was to determine the f e a s i b i l i t y of the e x i s t i n g machine, evaluate i t s performance and observe the general machine behaviour. The machine performance i s a function of the i n d i v i d u a l parts or systems. In order to determine where the problems exist i t i s necessary to i s o l a t e the systems and t e s t t h e i r i n d i v i d u a l performances. This was done by t e s t i n g the performance of the seed s e l e c t i o n system f i r s t and then t e s t i n g the performance of the combined transporting and planting system. The combined systems were then evaluated separately by observations made during the experiments. The test f o r the seed s e l e c t i o n system was conducted by adjusting the a i r brush pressure, the vacuum pressure and the seed removal pressure to give the most dependable v i s u a l r e s u l t s . The objective was to maximize the number of single seeds selected. No record of the r e s u l t i n g adjustments was attempted because i n the low operating ranges used, the high pressure regulator gauge readings on the laboratory a i r supply system were not dependable. The seed s e l e c t i o n unit was operated f o r 1,000 cycles and the number of zero, double and t r i p l e pickups were counted. The gauges were re-adjusted v i s u a l l y and a second test was conducted s i m i l a r to the f i r s t but with s l i g h t l y d i f f e r e n t pressure and vacuum settings. Results of these tests are given i n Table I. TABLE I TEST RESULTS OF SEED SELECTION UNIT Frequency of Seeds Picked Test #1 Test #2 Average Single seed/cycle 66.1% 66.8% 66.4% Double seeds/cycle _ ?0.9% 15.7% 18.3% T r i p l e seeds/cycle 1.2% .09% .1% Tota l no seeds 1,115 1,009 2,124 Average no seeds/cycle 1.12 1.01 1.06 The average t o t a l seeding rate of 1.06 seeds/cycle i s s a t i s f a c t o r y but the d i s t r i b u t i o n about the mean i s too great. The minimum acceptable performance of t h i s machine should be 9 5% s i n g l e s , 3% doubles and 2% misses. An observa-t i o n made during the te s t i n g indicated a high of 15 consecu-t i v e singles p r i o r to a double or miss. This indicates a possible 94% single seeding rate and i f t h i s can be accom-plished i n c o n s i s t e n t l y i t should be able to be duplicated r e g u l a r l y . Other observations include that s i n g l e s , doubles and misses occur i n sets with as many as 10 misses and 6 doubles occurring consecutively. This implied that the pressure se t t i n g on the a i r brush nozzle was f l u c t u a t i n g . This was not detectable on the high pressure regulator gauge i n the laboratory a i r supply system, i n d i c a t i n g the need f o r a pressure regulator that w i l l d e l i v e r a consistent airflow accurately i n the 0 to 2 psig range. Another d i f f i c u l t y was due to the a i r brush design. The a i r brush should have been s i m i l a r to that used f o r the conifer p r e c i s i o n seeder (2) as uniformity of the airflow seems important. The momentum imparted on the seeds by the a i r brush airstream was s u f f i c i e n t to bounce the seeds out of the hopper. This problem prevented increasing the a i r brush flow and therefore r e s t r i c t e d the range of vacuum settings that could be used. A higher vacuum se t t i n g and a i r brush pressure combined with an a i r brush design change should improve the seed se l e c t i o n t o o l performance. In order to give the a i r brush and corresponding vacuum settings more range a new hopper design should be considered. One concept would be a hopper that i s completely enclosed at the seed drum surface but includes a v e r t i c a l vent large enough to expel the a i r from the a i r brush and separate the seeds from the airstream i n the process. As expected the con i c a l shaped seed o r i f i c e per-formed s a t i s f a c t o r i l y , confirming that r e l a t i v e seed symmetry i s almost as acceptable as perfect seed symmetry. The design could be improved, for instance, by r e s t r i c t i n g the large diameter of the seed o r i f i c e cone to seed length plus 10%. This w i l l allow the a i r brush to be placed closer to the po s i t i o n where the seeds are held which should help i n seed removal. Some consideration should be given to the co n i c a l angles f o r r e l a t i v e l y symmetrical seeds. For seeds r e l a t i v e l y symmetrical about one axis the cone angle should be larger and the o r i f i c e size smaller than the corresponding cone angle and o r i f i c e f o r t r u l y symmetrical seeds. One important f a c t o r that determines machine performance i s seed c l e a n l i -ness. I t i s imperative that the seed be clean before any assessment of maximum performance can be made. The seed used i n t h i s t e s t was commercially prepared for non-pr e c i s i o n seeding use. Properly cleaned seed could undoubtedly reduce the number of misses by 50%. A miss (experienced with the c o n i f e r p r e c i s i o n seeder) usually contained a small p a r t i c l e of seed coat i n the o r i f i c e blocking the vacuum and undoubtedly the same s i t u a t i o n occurred with the lettuce seed. The expected 95%, 3% and 2% d i s t r i b u t i o n should be well within the c a p a b i l i t i e s of t h i s seed s e l e c t i o n system. The following modifications should prove t h i s : (a) Clean seed (b) Pressure regulators accurate under 2 psig (c) An improved a i r brush with more range of adjustment (d) A new hopper complete with vent (e) New shape d e t a i l on the cone and seed o r i f i c e s i z e . A series of tests a f t e r each modification should show a continual improvement of the seed s e l e c t i o n system. After modification (d), each type of seed tested should have an independently designed seed o r i f i c e . Some s t i c k i n g due to l i m i t e d allowable seed d i s -charge pressure was evident i n t h i s design. To compensate f o r t h i s , a design modification on the seed receiver i s required, or a scavange cycle s i m i l a r to that used i n the c o n i f e r p r e c i s i o n seeder should be incorporated i n the control plate. A seed receiver design modification would allow increasing the discharge pressure without the p o s s i b i l i t y of blowing the seed out of the receiver. Two independent tests were conducted on the combined planting and transporting systems. Each was s i m i l a r to the 4 4 . seed s e l e c t i o n system t e s t . Pressure and vacuum conditions were adjusted to give what appeared to be the best consistent operating conditions. The number of seeds delivered by the probe cup was recorded f o r each cycle. Results of these tests are given i n Table IT. TABLE I I . TESTS RESULTS OF SEED DELIVERED BY PROBE Number of Cycles Number of cycles having — Zero seeds One seed Two seeds Three seeds 126 13 84 _6 210 19 The t o t a l percentage of seed delivered by the probe should be 100% of those delivered i n t o the seed receiver. From Table I i t i s seen that the t o t a l number of cycles expec-ted to d e l i v e r seeds to the receiver i s 1716 while from Table II i t i s seen that only 1415 probe cycles delivered seed. In other words, only 82% of the seed selected by the seed drum was delivered by the seed probe. It was d i f f i c u l t to determine where these seed losses occurred. Observations indicated that most of the losses occurred i n the seed trans-portation system although some losses also occurred i n the planting system. Seeds were often blown out of the seed receiver rather than dropped through the a i r flow regulator. There were two factors contributing to t h i s . A high discharge Totals 1,000 1,000 2,000 265 320 596 590 585 1,186 pressure was required to remove the seed. This caused tur-bulence i n the receiver and often supplied s u f f i c i e n t a i r flow to carry the seed out of the receiver. This problem w i l l be eliminated by the proposed receiver design change. The second f a c t o r was a i r leakage between the airflow regulator shaft and i t s enclosing outside c y l i n d e r . This leakage a i r flows out through the receiver often preventing the seed from f a l l i n g to the shaft. When t h i s occurred the seed was not in the proper p o s i t i o n to f a l l through the shaft hole at the intended time and remained i n the r e c e i v e r . This problem can be overcome by changing the valving arrangement and t h i s change i s discussed i n the general recommendation portion of t h i s report. Another l o c a t i o n where seed losses were noticed was i n the vent portion of the probe receiver and t h i s could be due to two factors. The transport system might have too much a i r moving through i t r e s u l t i n g i n a large enough vent v e l o c i t y to carry the seeds out of the probe receiver. The second problem could be too much turbulence i n the probe rece i v e r , causing the seed to bounce near the venting portion on the top. The new valving arrangement should solve the a i r volume problem while the second problem could be a l l e v i a t e d by increasing the .dimensions of the probe r e c e i v e r . . Seed damage appeared minimal with a maximum estimate of 2%. There are two areas where t h i s damage could occur. The f i r s t i s between the probe and the bottom probe guide where there i s a p o s s i b i l i t y of jamming. The new valving arrangement and/or the change i n dimensions of the probe receiver could correct t h i s . The second area i s between the probe t i p and the spring loaded valve where there i s a p o s s i b i l i t y of crushing seeds. This can be avoided by making the countersink deeper than the seed length and modifying the spring loaded valve so i t i s 9 0° to the probe centerline when i t i s closed. The recommended modification sequence to improve the transport and planting systems i s : (a) Implement a new a i r flow valving arrangement (b) Increase the dimensions of the probe receiver (c) Build a spring loaded valve seated at 9 0° to the probe. The piston arrangement worked s a t i s f a c t o r i l y although leaks occurred around the a i r flow control valve. Furthermore the long lead l i n e s offered enough resistance to the flow that increasing the a i r flow rate i n and out at the piston i s possible. The biggest problem i s the fix e d f i r i n g time of the piston due to the s p e c i f i c d i s t r i b u t i o n of cycles on the valve shaft. These problems can be overcome by changing the valve arrangement. These changes are discussed i n the general recommendations. The r e s u l t s of the t o t a l combined system are predicted using the independent t e s t s . Since the machine operates as a series unit the following i s assumed: ( R e l i a b i l i t y of Seed Selection) X ( R e l i a b i l i t y of Transport and Planting) = R e l i a b i l i t y of the machine. From Tables I and II i t i s seen that of a t o t a l of 2124 seeds selected by the seed drum only 166 3 were delivered to the probe. On t h i s b a s i s , assuming the planting system i s independent of whether the seeds are s i n g l e s , doubles or t r i p l e s , the r e l i a b i l i t y of the combined system i s 0.7 84. The t o t a l machine r e l i a b i l i t y f o r seed placement then i s : Singles = .664 X .784 = .521 Doubles = .183 X .784 = .144 T r i p l e s = .01 X .784 = .00784 For 2000 c y c l e s , using the machine r e l i a b i l i t y the estimated r e s u l t s are: Singles = 2000 X .521 = 1,042 seeds Doubles = 2000 X .144 X 2 = 576 seeds T r i p l e s = 2000 X .00784 X 3 = 47 seeds Total = 1,665 seeds From Table II the actual number of seeds delivered i n 2000 cycles were: Singles = 1,186 seeds Doubles = 420 seeds T r i p l e s = 57 seeds Total = 1,66 3 seeds 48. This above method of measuring machine performance can be used as a technique to determine the approximate e f f e c t of i n d i v i d u a l modifications on the performance of the t o t a l machine. The machine w i l l be p r a c t i c a l i f the t o t a l machine r e l i a b i l i t y f o r single seeds exceeds 0.9. 3 . 6 P r e c i s i o n Seeder Recommendations The simple r o t a t i n g valves used i n the t e s t model can be machined to overcome leakage between the inner r o t a t i n g shafts and outer cy l i n d e r s . They have an inherent weakness however that cannot be overcome. This i s because the "on" or " o f f " time on these valves i s fixed by the mechanical d i s t r i b u t i o n of holes and grooves on the shafts making the valve p o s i t i o n independent of the p o s i t i o n of the device i t i s c o n t r o l l i n g . It i s therefore recommended that the mechanical valves be replaced with microswitch activated a i r solenoids. The probe airflow regulator should be replaced by a timing cam that operates a microswitch which i n turn activates two a i r solenoids. One solenoid allows a i r into the top portion of the piston while the other simultaneously opens the exhaust below the piston. A second microswitch i s required to activate an a i r solenoid to allow a i r into the bottom of the piston and to activate a second solenoid to open the exhaust at the top end of the piston. This micro-switch must be activated by the piston p o s i t i o n and must also override the i n i t i a l microswitch cl o s i n g the bottom exhaust and the top i n l e t . Including t h i s type of control has two advantages. It eliminates leakage and minimizes the cycle time f o r the probe i n the extended p o s i t i o n . A timer safety device would have to be included. In t h i s way, i f an obstacle prevented the probe from extending to where i t can activate the second microswitch, the timer would return the probe automatically. The solenoids should be located close to the piston and cyli n d e r and should use large a i r l i n e s to minimize f r i c t i o n losses. The a i r flow regulator f o r the transport mechanism should also be another cam operated microswitch to control an a i r solenoid. The microswitch should be adjustable to control the a i r solenoid "on" and " o f f " time. This w i l l enable the system to use a high pressure a i r surge to carry the seed to the probe receiver then cease further a i r flow, stopping turbulence and therefore allowing the seed s u f f i c i e n t time to drop into p o s i t i o n before the probe f i r i n g cycle begins. Some measurements should be taken to determine the siz e range of h o r t i c u l t u r a l seeds i n order to design the transport and planting mechanisms to operate with the e n t i r e range of seeds. I f the si z e range i s too large then there may have to be two or three d i f f e r e n t optional sized systems that are purchased to meet a grower's s p e c i f i c need. The f i n a l concept of the p r e c i s i o n seeder i s to operate i t i n conjunction with the mulch layer applier. The seeder i s eventually to be timed with the mulch paper apply-ing rate and by varying the drive r a t i o between the a p p l i e r and the seeder the spacing of the seeds i n the d i r e c t i o n of t r a v e l can be adjusted. Side spacing w i l l be adjusted by changing the distance between multiple p r e c i s i o n seeders. Cost and f e a s i b i l i t y studies should be done com-paring the use of carburetor vacuum or a vacuum pump and a s i m i l a r comparative study between i n s t a l l i n g a compressor on t r a c t o r s or using compressed a i r cylinders. 4. DESIGN OF THE MULCH LAYER APPLIER A machine which w i l l apply a mulch layer to the s o i l surface must perform two functions. The machine must be capable of preparing the s o i l f o r the mulch layer and must also be capable of applying the mulch layer on the prepared s o i l surface. Two important unknowns have to be considered f o r s o i l preparation. The s o i l reaction to an applied load has to be determined i n order to design a machine to perform a given series of operations, while the l i m i t i n g forces to be used i n applying the mulch layer also have to be determined. A t e s t was undertaken to determine the reaction of a s o i l to an applied load and the r e s u l t i n g forces due to t h i s reaction. A scale r o l l e r was fabricated and used as a penetrometer on an Instron apparatus. A confined s o i l sample was placed on a compression c e l l and the r o l l e r pushed into the s o i l at a constant penetration rate. The forces and sinkages were recorded at regular i n t e r v a l s and the r e s u l t s were plotted using the Bernstein equation. The curve was a good f i t but due to a lack of understanding of the exact s o i l r e action a second set of data were obtained using the same conditions and a round penetrometer probe. A s i m i l a r curve was p l o t t e d , but the two curves had d i f f e r e n t constants. A d e t a i l e d attempt was made, to derive a -soil reaction pattern that would explain the d i f f e r e n t curves. It was assumed that the manner i n which the s o i l would react to a load would be the same i n both cases but that shape of the applied load would vary the d i s t r i b u t i o n of the s o i l r e action, r e s u l t i n g i n d i f f e r e n t t o t a l r e s u l t s . Several computer programs were run assuming d i f f e r e n t s o i l reactions i n an e f f o r t to corre-l a t e the two r e s u l t i n g curves. Assumed reactions could, i n no way, account f o r the di f f e r e n c e s , so i t was assumed that any further attempt to use any of these r e s u l t s f o r p r e d i c t i n g s o i l reactions f o r a f u l l scale load would be completely erroneous. One i n t e r e s t i n g observation i s the accuracy of the Bernstein equation derived f o r each shape. Apparently, regardless of the d i s t r i b u t i o n of the s o i l r e a c t i o n , within one shape, the exponential r e l a t i o n s h i p between pressure and sinkage i s v a l i d . Considering that one obvious reaction i s density change under an applied load, an assumption was made that the s o i l density change i s exponential with an applied load and an e f f o r t was made to solve the problem i n t h i s manner. The r e s u l t of t h i s e f f o r t i s the beginning of a t h e o r e t i c a l approach to c o r r e l a t i n g s o i l reactions r e s u l t i n g from density changes (3) to applied loads. However, no easy way was determined to evaluate the constants so the approach was not h e l p f u l f o r t h i s p a r t i c u l a r problem. As a r e s u l t of t h i s i n a b i l i t y to measure the s o i l forces and determine the s o i l reactions, the design of the ground- preparation unit became.-more of- an estimating procedure* than a design problem. The design l i m i t a t i o n s for the mulch applying section of the machine were calculated from t e s t i n g newsprint at a .constant s t r a i n rate of 0.5 cm per minute. Observations made during t e s t i n g of newsprint s t r i p s indicate that room dry newsprint i s e l a s t i c i n the lower stress and s t r a i n regions. The e l a s t i c l i m i t i s approximately 2 5% of the rupture point. Table III presents the force required to rupture various samples of room dry newsprint. The lowest recorded rupture force was 0.977 l b / i n width while the e l a s t i c l i m i t was reached at an average load of 0.244 l b / i n width. From these values, i t appears that the maximum tension used i n removing newsprint from a r o l l should be limi t e d to 0.15 l b / i n width (2/3 of the e l a s t i c l i m i t ) . For s t r i p s 6 8 inches wide, the maximum allow-able force w i l l be 11 lbs . Limiting the force during paper ap p l i c a t i o n to 11 lbs should prevent any permanent deformation or r e s i d u a l i n t e r n a l stresses i n the mulch layer. Table IV l i s t s the forces required to rupture water-saturated newsprint. Saturated newsprint did not have an e l a s t i c region and was time dependent. When considering wet newsprint (such as a mulch layer that has been placed on the s o i l and wetted by i r r i g a t i o n ) i t i s safe to assume that the paper i s p l a s t i c i n nature and that i f a force i s applied to the paper i t w i l l continue to creep u n t i l the stresses reach zero or the paper y i e l d s . Comparing the r e s u l t s i n Table IV with those i n Table III shows that the rupture strength of dry newsprint i s approximately four times the strength of wet newsprint. Table V shows the maximum elongation at rupture of TABLE III RESULTS OF TENSION TESTS ON NEWSPRINT USING THE INSTRON APPARATUS Each sample i s 1.865 inches long X 1 inch wide X .0025 inches t h i c k . The newsprint i s room dry. Sample No. Fai l u r e Force (lbs) 1 .977 2 . 926 3 1.023 4 1.102 5 1.146 6 1.072 7 1.159 8 1.164 9 1.195 10 1.182 11 1.202 12 1.078 13 1.058 14 1.102 Mean 1.099 TABLE IV RESULTS OF TENSION TESTS ON NEWSPRINT USING THE INSTRON APPARATUS Each sample i s 1.865 inches X 1.0 inch X .0025 inch The center portion of each specimen was immersed i n water f o r approximately one minute u n t i l a one inch length was saturated Sample No. Failur e Force (lbs) 1 .256 2 .242 3 .229 4 .249 5 .210 6 .257 7 .290 , . e . , . . . . . . . . . . .., • ••• • '•• • • • • v . - - - . -.2 82 9 .285 10 .260 11 .280 12 .254 13 .284 14 .273 15 .249 16 .262 17 .273 Mean .2 61 TABLE V RESULTS OF STRAIN TESTING NEWSPRINT SAMPLES IN THE INSTRON APPARATUS The change i n length recorded i s the maximum occurring when the sample f a i l s i n tension. The samples are 1.865 inches X 1.0 inch X .0025 inch. The newsprint i s room dry. Maximum s t r a i n i s change i n l e n g t h / f i n a l length. Sample No. Maximum Elongation Maximum Stra i n (inches) finches-, inches 1 . 0557 .0290 2 . 0539 . 0281 3 .0594 .0309 4 . 0569 .0296 5 .0591 .0307 6 . 0547 .0285 7 .0547 .0285 8 . 0571 .0297 9 .0492 .0257 Mean .0290 TABLE VI RESULTS OF STRAIN TESTING NEWSPRINT SAMPLES IN THE INSTRON APPARATUS Maximum elongation occurs at the time when the sample f a i l s i n tension. Maximum s t r a i n i s the change i n l e n g t h / f i n a l length. The samples are saturated over a volume of 1 inch X 1 inch X .0025 inch a f t e r immersion i n water for approximately one minute. Sample No. Maximum Elongation Maximum Stra i n (inches) finches v inches 1 . 0284 .0276 2 .0314 .0304 3 .0286 .2078 4 . 0259 .0252 5 . 330 .0319 6 . 0320 .0310 7 .0235 .0235 8 .0460 .0440 9 . 0397 .0382 Mean .0310 room dry newsprint. The average s t r a i n i s .029 i n / i n . Table VI gives the same r e s u l t s f o r newsprint which has been immersed i n water f o r approximately one minute. Under the l a t t e r con-di t i o n s the average s t r a i n i s .031 i n / i n . Comparing the two tables indicates that the difference between the average maximum st r a i n s f o r wet and dry newsprint i s only 7%. From these r e s u l t s i t appears that the main design c r i t e r i o n w i l l be l i m i t i n g the stresses i n the paper layer such that creep r e l i e f of these stresses w i l l not exceed the maximum allowable s t r a i n . Using'a design s t r a i n of 50% of the average s t r a i n at rupture, the allowable s t r a i n i s .015 i n / i n . Assuming that one h a l f of t h i s s t r a i n occurs when the newsprint i s placed on the ground with fixed ends, and that the other h a l f occurs due to creep r e l i e f of the accompanying stresses, the maximum allowable s t r a i n to which the newsprint may be exposed during a p p l i c a t i o n • i s .008 i n / i n . Consider a lettuce bed with a top width of 54 inches as shown i n Figure 4. Assume that a 68 inch wide layer of newsprint i s used to cover the bed. A seven inch width of the newsprint i s placed beneath the s o i l surface, on e i t h e r side of the bed, to hold the mulch layer i n place. The 14 inch width of newsprint below the s o i l surface must absorb the t o t a l force placed on the newsprint by the paper tension control mechanism i n the mulch applying machine. Assuming also that the 14 inch width becomes saturated immediately upon contact with the s o i l and that the s t r e s s - s t r a i n r e l a t i o n s h i p i n the paper i s l i n e a r , the average allowable force that may be applied to the paper per inch of width i s : ( f a i l u r e force for saturated paper) X (allowable strain) ( s t r a i n at f a i l u r e for saturated paper) Using the previously presented data for newsprint, the maximum allowable force required to actuate a paper tension control mechanism i s : (.261)(.008)(l»O = 0 . 9 4 3 l b s . .031 4.1 S o i l Preparation Unit The s o i l preparation unit must accomplish three objectives. The f i r s t objective i s to smooth out a l l s o i l surfaces that w i l l contact the mulch layer. This i s to prevent stress concentrations i n the mulch layer during a p p l i c a t i o n . The second objective i s to compact the s o i l surface s u f f i c i e n t l y so that s o i l s e t t l i n g w i l l be i n s u f f i c i e n t to create stresses large enough to tear the mulch layer. The t h i r d objective i s to place the edges of the mulch layer beneath the s o i l surface with s u f f i c i e n t s o i l compaction to prevent the mulch from moving. The f i r s t two objectives can be accomplished by a combination of s o i l t o o l s . The f i r s t t o o l i s a r o l l e r (Figure 30). The r o l l e r simultaneously smooths and compresses the s o i l surface, and minimizes the bulldozing e f f e c t i n front of the mulch applier. In conjunction with the r o l l e r , two side plates (Figure 30-A) smooth and compact the s o i l at t h e i r inside edges. The cutting edges of the v e r t i c a l side plates FIGURE 30. Roller and Side Plates FIGURE 31. S l i d e r are angled at 45° to move the s o i l from i n front of the side plates to t h e i r inside edges. Some bulldozing w i l l undoubtedly occur but the e f f e c t at the inside edges should be reduced by the r o l l e r . In d i s p l a c i n g the s o i l from the lead edge, the side plates create a groove i n the s o i l at the sides of the mulch layer that w i l l eventually serve to hold the mulch layer i n po s i t i o n . The inside edges of the side plates are part of the s l i d e r (Figure 31-A), bent at 90° to the s l i d e r while the outside edges are separate s t e e l plates bolted to the inside edges at the bottom, and to the main machine frame at the top. This r e s u l t s i n a hollow groove between the inside and out-side edges to act as a guide f o r placing the mulch edges within the s o i l . The s l i d e r and side plates act as a t r a n s i t i o n surface f o r the mulch. The s l i d e r serves to a l i g n the mulch p a r a l l e l to the s o i l surface while the hollow side plates serve as a t r a n s i t i o n for placing the mulch layer edges beneath the s o i l surface (Figure 32). The material thickness of the inside side plates and s l i d e r serves as an add i t i o n a l safety f a c t o r f o r l i m i t i n g mulch layer stresses as follows. The peripheral distance over the top edge of the s l i d e r and side plates on which the paper i s guided i s greater than peripheral distance over the bottom surfaces that contact the s o i l . This distance difference should be s u f f i c i e n t to allow the com-pressed s o i l to expand, when the compressive forces of the s o i l preparation unit are removed, without adding a d d i t i o n a l FIGURE 32. S l i d e r and Orientation Controls FIGURE 33. Drive System stresses to the mulch layer. I t i s therefore expected that the prepared s o i l surfaces w i l l uniformally expand to f i t the mulch layer dimensions set by the machine. The f i n a l requirement of the s o i l preparation unit i s to f i l l the s o i l grooves formed by the side plates. The grooves must be f i l l e d with s u f f i c i e n t s o i l so that f r i c t i o n between the mulch and the compacted s o i l w i l l prevent mulch movement. The l i m i t i n g factor f o r compaction i s the degree of s o i l packing on the inside mulch edges. I f s o i l compaction during f i l l i n g exceeds compaction of the s o i l i n s i d e the mulch edges, a displacement of the mulch w i l l occur that could increase the mulch stresses. A further r e s t r i c t i o n i s that no movement of the f i l l i n g s o i l should occur p a r a l l e l to the mulch edges. Such displacement could p u l l the mulch edges, introducing further stresses. In an e f f o r t to keep the back-f i l l i n g motion perpendicular to the mulch edges a set of ro t a t i n g cones (Figure 32-A) are used. A study by Kim (4) using cone penetrometers indicated that displacement of the s o i l to t h i s type of applied load was quite uniform i n d i r e c -tions perpendicular to the applied force. To obtain the desired uniform displacement r o t a t i n g cones are used, each ' approximately a continuously operating penetrometer. The t o t a l requirement of the s o i l preparation unit i s to produce a smooth continuous three sided s o i l block, and to cover the block with paper mulch without disturbing the prepared block. 4.2 The Mulch Layer C o n t r o l System The a c t u a l mulch l a y e r c o n t r o l system i s s i m i l a r t o t h a t p r e v i o u s l y proposed. The f o r c e l i m i t a t i o n s d e r i v e d e a r l i e r apply t o the c o n t r o l system. I t i s assumed t h a t the l a r g e s t f o r c e i n v o l v e d i n mulch a p p l i c a t i o n i s the f o r c e r e q u i r e d t o p u l l the mulch paper from i t s r o l l . The f o r c e s r e q u i r e d to bend the paper edges are c o n s i d e r e d n e g l i g i b l e as w e l l as the f o r c e s r e q u i r e d t o keep the mulch i n a c e n t e r e d p o s i t i o n on the paper f e e d i n g p l a t e s . For the above r e a s o n , the powered r o l l e r ( F i g u r e 3 3-C) i s l o c a t e d c l o s e t o the paper r o l l ( F i g u r e 34). The mulch t e n s i o n must c o n t i n u o u s l y be monitored between the s o i l and the d r i v e r o l l e r , i f the mulch s t r e s s i s t o be kept below d e s i g n l i m i t s . The mulch changes d i r e c t i o n by 90° ( F i g u r e 34) as i t passes onto the s l i d e r ( F i g u r e r 31-A). A t e n s i o n r o l l e r ( F i g u r e 32-D) i s l o c a t e d a t the apex o f the t r i a n g l e the mulch makes between the f i x e d p o s i t i o n r o l l e r , the t e n s i o n r o l l e r and the f i x e d p o s i t i o n c o n t r o l r o l l e r s ( F i g u r e 32-C). The t e n s i o n r o l l e r i s f r e e t o r o t a t e about a f i x e d a x i s ( F i g u r e 35-A) and when the t e n s i o n i n the mulch reaches a c e r t a i n l e v e l the f o r c e moves the t e n s i o n r o l l e r . The only t e n s i o n on the mulch i s t h a t due t o the t e n s i o n r o l l e r r e s i s t a n c e a t the t r i a n g l e ..apex... .-.The. c o n t r o l . . r p l l e r s , are., .used t o form.a.p.ort.iQn. of. ...the , s e n s i n g t r i a n g l e and t o keep the mulch c e n t e r e d smoothly on the s l i d e r . They are designed t o u t i l i z e the f r i c t i o n between them and the mulch as a d r i v i n g f o r c e and t h e i r angle FIGURE 35. Rotation Axis f o r Tension Roller are to be adjusted to convert some of t h i s force to a s l i d e p u l l to center and hold the mulch firmly on the s l i d e r . The mulch i s bent 90° at the edges and held i n p o s i t i o n f o r packing underground by a set of bending r o l l e r s (Figure 32-B). At t h i s point the mulch w i l l leave the machine as a pre-formed covering f o r the prepared smooth three sided continuous s o i l block the s o i l preparation unit has produced. The only external force applied as resistance to p u l l i n g the paper from the machine i s due to the weight and r o t a t i o n a l resistance of the tension sensing r o l l e r assembly. The r o l l e r rotates about fi x e d points (Figure 35-A) and t h i s r o t a t i o n i s used to vary the resistance of a variable r e s i s t o r (Figure 33-B). The variable r e s i s t o r i s connected i n series with a 12 v o l t battery operated D.C. motor (Figure 33-A), which i s connected by b e l t to the powered r o l l e r used to remove mulch from the r o l l . A l l these units together form a feedback system. The p o s i t i o n of the tension sensing r o l l e r i s proportional to the mulch tension, c o n t r o l l i n g the variable r e s i s t o r s e t t i n g , and determining the feed r o l l e r speed which a l t e r s the mulch tension appropriately. As the tension sensing r o l l e r supplies the most tension during mulch removal, there i s an adjustable counterbalance to minimize t h i s force (Figure 36-A). When adjusted properly the only force required to r e p o s i t i o n the tension r o l l e r i s the force required to overcome the mechanical f r i c t i o n of the variable r e s i s t o r . This force should be well FIGURE 36. Tension Roller Counterbalance within the l i m i t a t i o n s of the mulch strength. 4.3 Machine Operation The machine i s designed to operate i n the following manner. The machine i s placed on the s o i l and moved i t s f u l l length, leaving two grooves i n the s o i l between the r o t a t i n g cones and the side plates. The mulch i s pulled by hand from the end of the s l i d e r u n t i l i t reaches the point where the cones have b a c k f i l l e d the groove. I n i t i a l l y , an external force i s used to f i x the mulch end. The machine i s now moved ahead u n t i l the cones have packed the mulch edges within the s o i l so that the r e s u l t i n g f r i c t i o n i s s u f f i c i e n t to p u l l the mulch from the machine. As the machine moves ahead the mulch tension increases, l i f t i n g the tension r o l l e r , adjusting the feed r o l l e r speed, and increasing the mulch removal rate. I f the mulch i s removed too r a p i d l y , the tension reduces, allowing the tension r o l l e r to drop, slowing the rate of mulch removal. Thus the mulch w i l l be placed on the s o i l under tension within the l i m i t a t i o n s of the paper strength. The tension stress w i l l o s c i l l a t e between acceptable l i m i t s . A f i e l d t e s t i s necessary to determine i f the machine works s u i t a b l y . The f i e l d test should i n i t i a l l y be a test of the s o i l preparation unit, followed by a te s t of the entire process. 4 . 4 Anticipated Problems The difference i n f r i c t i o n factor between the control r o l l e r s and mulch and between the mulch and s l i d e r i s not as 67. large as intended. Any attempt to develop enough f r i c t i o n force between the mulch and control r o l l e r s , to get the f u l l benefit of the r o l l e r s , r e s u l t s i n an unacceptable f r i c t i o n drag between the mulch and the s l i d e r . There may not be any need for centering the paper i f the r o t a t i n g cones apply equal force on both sides of the mulch. In t h i s case, the mulch w i l l remain smooth and centered over the s l i d e r without the control r o l l e r s . However, i f t e s t i n g indicates a center-ing control i s necessary, i t may be necessary to attach t e f l o n s t r i p s under the paper to reduce s l i d e r f r i c t i o n . The e x i s t i n g system uses a simple, variable r e s i s t o r i n series with the paper drive motor. This may reduce the motor torque at lower speeds to a l e v e l below the required drive r o l l e r torque. Should t h i s occur a more complicated c i r c u i t i s available that w i l l reduce the motor speed without s i g n i f i c a n t l y reducing i t s torque. Should the bending and control r o l l e r s both present a problem the r o l l e r s should be replaced with a s t e e l guide sheath. This should extend from the control r o l l e r p o s i t i o n to the rear of the machine. The sheath should have an inside clearance equal to the mulch thickness plus 20 percent and' the inside width should be equal to the mulch width plus 1/16 inch. The sheath center w i l l be p a r a l l e l to the s l i d e r from the control r o l l e r p o s i t i o n to the rear of the machine. The sheath outer edges w i l l be p a r a l l e l to the sheath center at the control r o l l e r p o s i t i o n but w i l l bend gradually so that at the rear of the machine they w i l l be perpendicular to the center. The paper w i l l enter the sheath at the control r o l l e r p o s i t i o n and w i l l gradually be bent by the sheath con tours so i t w i l l leave the sheath with the edges below the s o i l surface forming a complete covering for the s o i l block. 69-5. GENERAL CONCLUSIONS 1. I n i t i a l r e s u l t s of the pr e c i s i o n seeder tests indicated the p r a c t i c a l f e a s i b i l i t y of the approach and j u s t i f i e s a program to modify the e x i s t i n g machine and i n i t i a t e a series of tests to es t a b l i s h i t s performance. 2. The pr e c i s i o n seeder can be developed and used indepen-dently of the mulch layer applier. 3. Test r e s u l t s on seed damage are needed but are not p r a c t i c a l u n t i l a l l mechanical problems of the seeder are solved. 4. The mulch layer applier must be f i e l d tested and modified before a conclusion regarding i t s p r a c t i a l f e a s i b i -l i t y can be reached. 5. Detailed studies w i l l be required to determine the e f f e c t of compacting the s o i l and the e f f e c t of mulch accumulation on plant growth. 6. Using a sheath f o r c o n t r o l l i n g the mulch i s much more suitable than using r o l l e r s . However, the present model should test the general concept. 7. The combined projects appear to have enough p o t e n t i a l to warrent further development, t e s t i n g and modifications. The costs to completely determine the f e a s i b i l i t y of the machines are estimated as follows: Precision seeder modifications and t e s t i n g $15,000 Mulch layer t e s t i n g and modifications 15,000 Combined t e s t i n g and modifications 10,000 Suggested associated studies 15,000 Overhead 11,000 T o t a l Costs $66 ,000 The necessary sales required to cover the development costs are estimated at 100 u n i t s , based on the previously estimated r e t a i l p r i c e . This has not been discussed i n the main report but i s included as a guide f o r future recommended investigations. 71. REFERENCES 1. Dorling, M.J. Mid-Season Lettuce Costs of Production -Case Studies i n the Cloverdale Area of B r i t i s h  Columbia. Vancouver: University of B r i t i s h Columbia, Department of A g r i c u l t u r a l Economics, (1970). 2. Nyborg, E.O. , McLeod, CD. and Narsted, B.C. A Precis i o n Seeder f o r Container Production of Coniferous Seedlings. Paper No. 72-314, presented at 1972 Annual Meeting, Canadian Society of A g r i c u l t u r a l Engineering, Charlottetown, (June 26-29, 1972). 3. McLeod, CD. , Nyborg, E.O. Theoretical S o i l Block Formation Under Penetrometers. Paper No. 72-308, presented at 1972 Annual Meeting Canadian Society of A g r i c u l t u r a l Engineering, Charlottetown (June 26-29, 1972). 4. Kim, J . I . The Deformation and Properties of Cohesive S o i l i n Relation to Soil-Machine Systems. Department of Mechanical Engineering, University of B r i t i s h Columbia, September 1970. 

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