UBC Faculty Research and Publications

Flowering and regrowth of hairy vetch cultivars used for pollinator forage and reduced tillage Koebel, Alisa; Furey, George; Riseman, Andrew 2014

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Running	  Head:	  FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   1	  	             Flowering and Regrowth of Hairy Vetch Cultivars Used for Pollinator Forage and Reduced Tillage Alisa Koebel, George Furey, and Andrew Riseman University of British Columbia GRS 497B    FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   2	  	   	  Contents	  INTRODUCTION	  ............................................................................................................................................	  3	  Hairy	  Vetch	  ..............................................................................................................................................	  3	  Pollination	  ................................................................................................................................................	  5	  Tillage	  .......................................................................................................................................................	  7	  Objectives	  ................................................................................................................................................	  8	  METHODS	  ....................................................................................................................................................	  9	  Experimental	  Design	  and	  Planting	  ...........................................................................................................	  9	  Flowering	  .................................................................................................................................................	  9	  Termination	  and	  Regrowth	  ......................................................................................................................	  9	  Statistical	  Analysis	  ..................................................................................................................................	  10	  RESULTS	  .....................................................................................................................................................	  11	  Flowering	  ...............................................................................................................................................	  11	  Regrowth	  ...............................................................................................................................................	  11	  DISCUSSION	  ...............................................................................................................................................	  11	  Flowering	  ...............................................................................................................................................	  11	  Regrowth	  ...............................................................................................................................................	  12	  Error	  .......................................................................................................................................................	  12	  Recommendations	  .................................................................................................................................	  13	  Future	  Research	  .....................................................................................................................................	  13	  Conclusion	  .............................................................................................................................................	  13	  REFERENCES	  ...............................................................................................................................................	  15	  APPENDIX	  A:	  TABLES	  ..................................................................................................................................	  18	  APPENDIX	  B:	  FIGURES	  ................................................................................................................................	  19	  	  	   	  FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   3	  	  INTRODUCTION	  In response to the many sustainability challenges faced by modern agriculture and surrounding “natural” habitat, agricultural production systems are increasingly being characterized as agro-ecosystems in recognition of their integration with the environment.   Within an agro-ecological paradigm, cover crops can be a valuable tool because they promote certain important ecosystem services.  Ecosystem services are functions of an ecosystem which provide a benefit to humans and can be categorized as provisioning, regulating, supporting, and cultural services (Zhang, Ricketts, Kremen, Carney, & Swinton, 2007).  In some cases, these ecosystem services have been linked to specific plant characteristics or functional traits such as flowering time, ability to fix nitrogen, and biomass production (Wilke & Snapp, 2008).  This study examines hairy vetch cultivars’ potential to provide services for pollinators and in the context of winter cover crop reduced till operations by measuring two functional traits: flowering time and regrowth.  This report first describes the characteristics of hairy vetch, then goes on to locate the potential role of cover crops in pollination and reduced-tillage organic systems.   Hairy	  Vetch	  Vetches are any plant of the leguminous genus Vicia.  The U.S. Department of Agriculture-funded cover crop handbook “Managing Cover Crops Profitably” lists hairy vetch (Vicia villosa Roth) and its close relative woollypod vetch (listed as V. villosa ssp. dasycarpa or V. dasycarpa) as two common cover crops in this genus (SARE, 2012).  Hairy vetch is the most winter-hardy of the genus (Brainard, Henshaw, & Snapp, 2012) and is considered one of the best legumes to plant in late fall where nitrogen fixation is a goal (Wilke & Snapp, 2008).  It also improves soil moisture, helps suppress weeds, and is drought-resistant (SARE, 2012). However, there are also certain risks associated with the use of hairy vetch, such as ineffective mechanical termination (Wayman et al., 2014); mixed pest effects (SARE, 2012); and FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   4	  	  regrowth that competes with cash crops (Brainard et al., 2012; Delate, Cwach, & Chase, 2011), dependent on termination method and timing (Mischler, Duiker, Curran, & Wilson, 2010).  While improved yields of corn following hairy vetch alone or with rye have been demonstrated in Maryland (Clark & Decker, 1997), reductions in corn yields of 42-92% were found in no-till plots in Iowa and were severe enough to cause economic loss (Delate et al., 2011), while hairy vetch cover had mixed effects on corn yield in Pennsylvania after no-till termination (Mischler et al., 2010).  In order to maximize the ecosystem services provided by hairy vetch and minimize the risks, Wilke & Snapp have proposed two strategies.  Both rely on the connection between plant traits and ecosystem functions, and recognize that these effects will vary according to local conditions and practices.  One is to breed for locally adapted varieties, a strategy made possible by the high levels of genetic variety in hairy vetch’s germplasm (Wilke & Snapp, 2008).  They enumerate 6 ecosystem functions and functional traits which should be balanced for optimum performance of a local vetch variety: winter hardiness, high specific leaf area to conserve soil moisture, optimization of flowering time to assist in no-till termination, greater soil nitrogen uptake, regrowth following grazing, and stress resistance (Wilke & Snapp, 2008).  They also caution against over-selecting for one trait to the detriment of others (Wilke & Snapp, 2008). The other strategy is the use of intraspecific variety; that is, planting a polyculture of hairy vetches with variation in functional traits (Wilke & Snapp, 2008).   There are also certain differences between hairy vetch and “Lana” woollypod vetch that might influence selection.  “Lana” attracts many beneficial insects and so has few pest problems, accumulates biomass early in the season, and is more heat tolerant (SARE, 2012), but has low specific leaf area (Wilke & Snapp, 2008), is less winter-hardy than hairy vetch, and can delay FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   5	  	  summer cash crop seeding by slowing soil drying (SARE, 2012).  However, these findings need to be evaluated in a local context.  Previous studies found that “Lana” flowers early compared to purple vetch (Vicia americana) (SARE, 2012).  Recently, an experiment in nearby western Washington found that “Lana” vetch reached termination stage before hairy vetch, but the authors recommended against its use in the region because of poor weed control (Wayman et al., 2014).  This study contributes to the local literature by comparing “Lana” with two hairy vetches which were bred to be early-flowering, and by comparing vetch monoculture with polyculture.   In this study, vetch and rye were grown in combination in order to evaluate the vetch varieties’ performance in conditions most resembling those likely to be used in the field.  Rye-vetch combinations are favoured because they have been shown to improve vetch overwintering and increase total vetch biomass (Jannink, Merrick, Liebman, & Dyck, 1997), delay termination resulting in greater nitrogen fixation, improve termination effectiveness when mowing, reduce leaching from vetch’s improved soil moisture (SARE, 2012), increase mulch biomass (possibly by supporting the vetch stalks), and increase mulch persistence due to the cellulose content of rye (Wayman et al., 2014) among other benefits, and because rye is more effective than vetch at suppressing weeds (Carr, Horsley, Gunderson, Winch, & Martin, 2013; Davis, 2010; SARE, 2012) and insect pests (SARE, 2012).   Pollination	  Pollination is a prime example of a provisioning ecosystem service.  The proportion of bee-mediated pollination attributable to honeybees and to wild bees is poorly known, but both have a significant role.  European honeybees, as an introduced species, can be less efficient at pollinating some crops because they are not as well adapted, though this is not uniformly found (Dohzono & Yokoyama, 2010).  For example, tomatoes and blueberries require buzz-pollination, which bumblebees and carpenter bees perform but honeybees do not (Bennett, 2012).  Although FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   6	  	  honeybees may be less efficient, they are frequently more numerous because they are social, thus increasing their impact (Bennett, 2012); however, a study of pollinator visits in New Jersey and Pennsylvania found that wild bees were the most common visitor for a majority of crops studied in those regions (Winfree & Williams, 2008).  Native bees are also more tolerant of a range of weather conditions.  In one study of pollination in apple orchards, it was found that during adverse weather events, the number of honeybee visits decreased but total fruit set remained constant as native bees increased their activity (Boyle, 1981).  Kremen et al. found that native bees could provide full pollination of watermelon farms in California if the field was organically managed and near natural habitat, but not otherwise; honeybee pollination was not sufficient in any treatment (Kremen, Williams, & Thorp, 2002).  In short, honeybees and wild bees have complex and overlapping roles in pollination.  Both are important, and both are in decline (Potts et al., 2010). Perhaps the best-known threat to honeybees is Colony Collapse Disorder (CCD), the causes of which are still being studied.  Recent research suggests that multiple and interacting factors are involved, including pathogens and parasites (Nazzi et al., 2012; Vanengelsdorp et al., 2009).  Knowledge of the threats to wild bees is similarly uncertain.  They may be in competition with introduced bees, suggested by the inverse relationship between the groups’ flower visitation rates (Dohzono & Yokoyama, 2010), though a Californian study found no impact of honeybees on wild bee populations (Kremen et al., 2002).  A literature review of studies investigating the impact of anthropogenic land use change on bee richness and abundance found that most of the relationships were not statistically significant; among significant relationships the negative outnumbered the positive, but impacts varied by taxa and scale (Winfree, Bartomeus, & Cariveau, 2011).  Other studies have found that natural habitat near agricultural fields positively affects the FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   7	  	  abundance of wild bees, and that they tend to be more active closer to forest edges (Bailey et al., 2014; Ricketts, 2004).  Westrich discusses the importance of forested area in terms of partial habitat, or habitat that provides only one or two of the resources required for nest-building bees to survive and reproduce, these being a nest site, nesting material, and sufficient food (Westrich, 1996).  Indeed, loss of plant biodiversity and floral resources are a proposed contributing factor to the decline of wild bees (Potts et al., 2010) and the most important limiting factor on local populations (Roulston & Goodell, 2011).  If adequate forage is lacking in the nearby natural habitat, cover crops are one way to provide it in cultivated areas.   Although some farmers are using them to temporally extend the availability of forage (Baker, 2014), little research has been done into the impact of cover crops on bees.  A crop rotation that includes fallows (Kuussaari, Hyvönen, & Härmä, 2011) and the use of ground cover – defined as herbs and grasses, and thus not generalizable to vetch – have been found to be beneficial (Saunders, Luck, & Mayfield, 2013).  However, the literature on oilseed rape as a mass-flowering crop in Germany may provide guidance on the possible benefits for pollinators of early-flowering vetch.  Presence of oilseed rape, which flowers in May before many other food resources are available to bees, is positively correlated with richness and abundance of solitary bees (Le Féon et al., 2013) and population density of bumblebees (Riedinger, Renner, Rundlöf, Steffan-Dewenter, & Holzschuh, 2013; Westphal, Steffan-Dewenter, & Tscharntke, 2003), possibly because it provides ample resources at the time of colony founding (Westphal et al., 2003).  However, some species may benefit at the expense of others (Diekötter, Kadoya, Peter, Wolters, & Jauker, 2010).   Tillage	  It has been shown that no-till termination of vetch is most effective at greater levels of flowering (Mischler et al., 2010).  Therefore, earlier flowering varieties can be terminated earlier FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   8	  	  and are preferable when preceding a cash crop that requires early seeding (Comis, 2008).  Reducing tillage is valuable because, although organic systems often rely upon tillage for weed control in lieu of herbicides, tillage also produces undesirable effects.  These include increased soil erosion and nutrient loss, disruption of microbial communities, and oxidation of carbon (Carr et al., 2013; Delate et al., 2011).  These and other problems have prompted some to adopt conservation tillage, an umbrella term for several tillage practices that leave at least 30% soil cover in order to reduce soil erosion to acceptable levels (SARE, 2012).  At the same time, no-till systems currently require herbicides to control weeds (Mischler et al., 2010).  In order to reap the benefits of both organic and reduced-tillage practices, cover crops are being explored for their potential to suppress weeds through competition, shading, and allelopathy, as well as to sequester carbon; prevent soil erosion; store nutrients; and, in the case of legumes, fix nitrogen (Delate et al., 2011; Mischler et al., 2010; SARE, 2012; Wayman et al., 2014).  The selection of a suitable cover crop may therefore allow organic producers to effectively reduce tillage.   If UBC Farm were to adopt some form of conservation tillage, information about flowering and regrowth would assist in selecting cover crops that meet their production and sustainability goals.  Additionally, there is some speculation that reduced tillage may allow native pollinators to nest in agricultural plots (Bailey et al., 2014). Objectives	  One objective is to compare the extent and timing of flowering of two early-flowering hairy vetch varieties, “Lana” woollypod vetch, and a vetch polyculture under conditions present at the UBC Farm site.  The second objective is to compare the amount of regrowth occurring after no-till termination for the same treatments.  This information is intended to help UBC Farm select a suitable cover crop if it were to adopt reduced till practices and to assist in its goal of enhancing habitat for pollinators by providing forage. FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   9	  	  METHODS	  Experimental	  Design	  and	  Planting	  The experiment was conducted at UBC Farm in a randomized complete block design with 5 blocks of 4 treatments.  Three of the treatments consisted of a single vetch variety grown with winter rye cv. unknown.  These were woollypod vetch (Vicia villosa ssp. dasycarpa/V. dasycarpa) cv. “Lana”, hairy vetch (Vicia villosa) cv. “Purple Bounty”, and hairy vetch cv. “Purple Prosperity”.  Both “Purple Bounty” and “Purple Prosperity” are early-flowering, winter-hardy varieties (Brainard et al., 2012; Comis, 2008).  The fourth treatment was a polyculture of all three vetches.  On September 26 2013, vetch was seeded at 20 kg/acre and rye at 80 kg/acre using a jang seeder; however, the density of established stands does not reflect this and was lower than planned.  Flowering	  The number of flowering racemes on 10 randomly selected stems in each plot was counted weekly from May 7 to June 4 2014 inclusive, based on the method described by Brainard, Henshaw, & Snapp (2012).  A raceme was counted as flowering if at least one bud had begun to open, and was also counted after flower death if the flower was still connected to the stem; unlike the Brainard et al. method, the presence of purple colour was not sufficient.  When both seed pods and flowers were present on a single raceme, both were recorded.   Termination	  and	  Regrowth	  The plots were terminated on June 4 2014 using a string trimmer.  This date was chosen because flowering rates were beginning to level off, suggesting the plants were near maximum flowering.  Higher rates of flowering have been shown to be correlated with lower rates of regrowth (Mischler et al., 2010).  Regrowth was measured 2 weeks following termination (June 18) using a grid quadrat with 81 points.  A count was recorded for every point which touched or FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   10	  	  lay directly above a living vetch plant.  Each plot had three measurements taken each week.  The sampling location was randomized for each measurement using a random number generator giving 1≤X≤7 where X is the number of paces taken along the length of the plot before laying out the quadrat; the plot’s width was approximately the same as that of the quadrat.  Results from these three counts were averaged to determine percent regrowth. Statistical	  Analysis	  All statistical tests were conducted with R version 3.1.1.  ANOVA and Tukey post-hoc tests were performed on the third week of flowering data (racemes per stem at May 21), which fit all assumptions of normality.  However, there was an issue with heteroskedasticity; plot 10 was removed in order to decrease this, which also resulted in a better fit of the normality plot and of the fitted line plot.  Our model compared differences in the number of flowering racemes per stem as the response variable and used treatment or the combination of treatment and block as explanatory variables.  The third week of flowering data was selected to analyze differences in flowering between cultivars because this would be a better time to terminate from a management perspective (personal communication, Tim Carter) and because our interest was in early flowering rather than final flowering.   ANOVA was also performed on the regrowth data with average percent regrowth as the response variable; again, treatment and treatment plus block were the explanatory variables for our model.  However, in order to look at the trend between flowering and regrowth, another ANOVA was performed on the final week of flowering data.   FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   11	  	  RESULTS	  Flowering	  Flowering data from May 21 showed differences in flowering between treatments (Table 1) with “Lana” vetch flowering earlier than all other treatments; “Purple Prosperity” and “Purple Bounty” were not different from one another (p = 0.3513), nor were “Purple Bounty” and the polyculture of all three (p = 0.3514) (Fig. 1).  Blocks were not significant.  A graph of flowering over time (Fig. 2) shows that all treatments have similar levels of maximum flowering, but that “Lana” peaked the earliest.  This is supported by ANOVA of the final week of flowering data, which found no difference by treatment or block (Fig. 3).   Regrowth	   	  Neither treatment nor block was significant in explaining the difference in regrowth.  There were several outliers which could not be removed for non-statistical reasons.  However, comparing the plots of mean regrowth and mean flowering racemes per stem at week 5 showed an inverse trend (Fig. 3 and Fig. 4).  The three treatments with equally high flowering at termination had very little regrowth, while “Purple Prosperity” had lower mean flowering and the highest mean regrowth as well as several plots with high values.    DISCUSSION	  Flowering	  “Purple Bounty” and “Purple Prosperity” were bred to be early-flowering (Brainard et al., 2012; Comis, 2008) and have been shown to flower earlier than a common hairy vetch from Oregon (Brainard et al., 2012).  However, we found that “Lana” woollypod vetch flowered earliest.  This is consistent with Wayman et al’s finding that “Lana” vetch flowered earlier than “Purple Bounty” for two consecutive seasons, as measured by the scale devised by Mischler et al (Mischler et al., 2010; Wayman et al., 2014), which was conducted in a similar climate, FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   12	  	  Washington state.  Wilke and Snapp also found that “Lana” flowered earlier than common hairy vetch and several other hairy vetch cultivars and landraces (Wilke & Snapp, 2008).  Our data adds to their results by demonstrating that “Lana” is an early-flowering variety by comparing it to early-flowering varieties that were not a subject of their study.   Regrowth	  Since it has been established that greater flowering at termination results in less regrowth (see Mischler et al., 2010), it was not surprising to see an inverse trend between the final week of flowering data and regrowth.  “Lana”, with the lowest mean regrowth and no high-value outliers, appears to be the best cultivar on this criterion as well as the earliest to flower.  “Purple Prosperity” is not likely to be a good choice as a cover crop at UBC Farm because of high regrowth even at late termination, which could result in competition with cash crops.   Error	  Brainard, Henshaw and Snapp found that flowering extent at a given time was greater if vetch was grown in combination with rye than if it was grown in monoculture, and they speculate that this may be due to shading or to competition for water, which accelerates flowering (Brainard et al., 2012).  Therefore, the flowering values we found cannot be generalized to hairy vetch monoculture.  Density is also likely to affect competition for water and nutrients, so lack of data on final stand density may confound our results.    The greatest source of error in regrowth arises from the short time period over which we gathered data.  More measurements over a longer time period would make it more likely that we could detect any existing difference between treatments, as might larger plot sizes.  Also, terminating the hairy vetch at an earlier time as recommended by farm management and measuring regrowth into the early cash crop growing season would provide data better suited to FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   13	  	  practical use and, since cultivar differences in flowering were more apparent earlier in the season, may be more likely to show a difference in regrowth between treatments.     Recommendations	  1) Plant “Lana” vetch near honeybees: “Lana” was found to be the earliest-flowering variety of hairy vetch and could provide forage early in the spring before many other food sources are available.  Future	  Research	  	  Hairy vetch should be terminated earlier and regrowth measured again to obtain more robust conclusions.  The date of termination should be determined in conversation with farm management and should be based on the seeding dates for cash crops.  Continuing to measure regrowth after cash crops have been planted would improve analysis of hairy vetch regrowth over the growing season.  Cucurbits would be a good choice of cash crop for initial analysis since it is the last family of crops planted at UBC Farm (personal communication, Tim Carter).   Cover crop management decisions would benefit from research into other functional traits of promising vetch cultivars like “Lana”, particularly biomass and nitrogen fixation, which have implications for other important ecosystem services such as weed suppression and cash crop yield.  In order to optimize vetch cover crop’s contribution to multiple ecosystem services, the Farm might benefit from a cost-benefit analysis comparing cultivars and termination times for their impact on all relevant functional traits.   Conclusion	  	   “Lana” vetch was found to flower earlier than the early-flowering cultivars “Purple Bounty” and “Purple Prosperity”.  We also noticed a trend between regrowth and flowering amount at termination suggesting an inverse relationship, which has been demonstrated with significance in previous studies.  On the basis of these results, “Purple Prosperity” is not FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   14	  	  recommended for use at UBC Farm, while “Lana” should be investigated for its other traits and potential to provide ecosystem services.  By providing early forage, “Lana” could be a useful part of UBC Farm’s strategy to support pollinator populations.  If the Farm wanted to incorporate reduced tillage into its management practices, “Lana” is also likely the best choice of the cultivars investigated because of its low regrowth due to early flowering.  On the basis of flowering and regrowth, “Lana” woollypod vetch is the best hairy vetch variety to contribute to UBC Farm’s sustainability goals.     FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   15	  	  REFERENCES	  Bailey, S., Requier, F., Nusillard, B., Roberts, S. P. M., Potts, S. G., & Bouget, C. (2014). Distance from forest edge affects bee pollinators in oilseed rape fields. 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FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   18	  	  APPENDIX	  A:	  TABLES	  	  Source of variation         df Sum of squares       Mean squares      F value     P     Treatment          3  50.981   16.9938            40.694  1.915e-07 Residuals                          15   6.264                0.4176              Table 1: Analysis of Variance Table for flowering racemes per stem measured on May 21st   FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   19	  	  APPENDIX	  B:	  FIGURES	   Fig. 1:  Flowering racemes per stem as measured on May 21 2014.  Red bars represent treatment means while circles represent individual data points.  Flowering = Treatment:  F = 40.69; df 3, 15; p = 1.915e-07.  Block was not significant at α = 0.05.  Treatments marked with the same letter are not significantly different at α = 0.05 according to Tukey post-hoc test.      Fig. 2: Average flowering racemes per stem of each plot over 5 weeks.  All plots were terminated on June 4 2014 after flowering counts were taken.  FLOWERING	  AND	  REGROWTH	  OF	  HAIRY	  VETCH	  CULTIVARS	   	   20	  	   Fig. 3:  Flowering racemes per stem measured on June 4 2014.  Red bars represent treatment means while circles represent individual data points.  Red bars represent treatment means while circles represent individual data points.  Neither treatment nor block were significant (α = 0.05).  When block was removed from the model (Regrowth = Treatment) F = 1.608; df 3, 15; p = 0.2294.    Fig. 4:  Percent regrowth measured two weeks after termination.  Red bars represent treatment means while circles represent individual data points.  Neither treatment nor block were significant (α = 0.05).  When block was removed from the model (Regrowth = Treatment) F = 0.6833; df 3, 16; p = 0.5751.   

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