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Effects of mulched and incorporated sawdust on some chemical and physical properties of Fraser Valley upland soil Dargie, George

Abstract

The study included field, greenhouse and laboratory experiments with sawdust used as mulch and incorporated with soil. The field experiments were conducted with hemlock sawdust mulches on Lynden silt loam at Abbotsford and on Everett sandy loam at Aldergrove. In both cases the crop was strawberries. Two depths of sawdust were used, two and four inches, and these were compared with clean cultivation, with and without sprinkler irrigation. Soil samples were taken in triplicate from three depths at intervals throughout the 1951 growing season and used for the determination of soil moisture. The 1951 season was one of the driest recorded and both depths of sawdust were very effective in conserving soil moisture. On the Lynden silt loam the sawdust maintained soil moisture at a satisfactory level for growth throughout the growing period and was as effective as sprinkler irrigation for this purpose. However, on Everett sandy loam, sprinkler irrigation maintained soil moisture in a more satisfactory manner. Samples taken from the Lynden soil after the mulches had been down a year, indicated a reduction in Humin I nitrogen and nitrate nitrogen had occured as a result of mulching. However, the differences were not great and a more significant reduction of total nitrogen and nitrate nitrogen was noted on the irrigated plots. In the greenhouse experiment, two sizes of cedar and hemlock sawdust were incorporated at two rates with Alderwood sandy loam, fertilized at two rates and planted with lettuce. After one year it was found that hemlock sawdust had increased the moisture equivalent and wilting percentage more than cedar had, but that the cedar mixtures gave a higher yield of lettuce. In all cases the differences were small but significant. Sawdust, when incorporated with the acidic soil, raised the pH slightly and increased the moisture equivalent, permanent wilting percentage and cation exchange capacity of the soil, the effect being greater for the higher rate of incorporation. Sawdust had the opposite effect on available moisture and lettuce yield. Apparent specific gravity of the soil was noticeably decreased as a result of the sawdust additions and a very large increase in non-capillary pore space occured. This was associated with a large increase in percolation rate. Capillary porosity was affected to a very small extent by the sawdust. Nitrogen fertilization (NH₄NO₃) increased soil acidity in the control soil and in the soil sawdust mixtures. Tests were conducted to determine the absorptic capacity of sawdust for water and ammonia. Size of sawdust affected the amount of water absorbed but not the amount of ammonia absorbed.

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