Improving Soil Health Through Cover Crop Based No-Till Organic Vegetable Production

Improving Soil Health Through Cover Crop Based No-Till Organic Vegetable Production

Summary

No-till techniques have gained attention as a means to reduce the negative impacts of intensive tillage, which is routinely used by organic farmers for weed control. Significant questions remain about the viability of no-till techniques in organic vegetable systems. This research compared cover crop species that could be used in organic no-till vegetable systems, measuring impacts on vegetable quality, yield, and soil health. Outcomes included the assessment of best management practices for organic no-till vegetable production in the upper Midwest. Long-term impacts include more effective no-till adoption among vegetable growers, leading to more effective organic weed management and improved soil health.SARE_Pfeiffer_photos

Objectives/Performance Targets

. All experiments were conducted on certified organic land (MOSA), using organic practices at the University of Wisconsin West Madison Agricultural Research Station. Research plots were seeded in the fall with four cover crop treatments (cereal rye, hairy vetch, winter wheat, and a rye/vetch mix) and a control plot of no cover in randomized complete block design including four replications. Cover crops were hand sown and lightly incorporated with a tractor mounted tiller at rates of 3 bushels/acre for winter wheat (variety not specified) and winter rye (variety not specified), 40 pounds/acre for hairy vetch (variety: ‘Purple Prosperity’), and rye-vetch mix (3 bushels/acre rye plus 40 pounds/acre vetch). Each plot measured 15 feet x 20 feet. Fall plant density counts were collected after cover crop emergence, counting all plants within a 0.25 square meter quadrat at two random locations in each plot.

In early May, prior to the cover crops exceeding 6 inches in growth, a 9-inch wide band was tilled using a walk-behind cultivator in each treatment plot where the vegetable crops will be sown. Strip tillage was necessary in this system to prevent the cereal grain cover crops within the planting zone from becoming too dense, thus inhibiting planting activities. Additionally, strip tillage facilitated soil warming, thus promoting crop growth. Cover crop biomass samples and soil samples were collected immediately prior to cover crop termination (Figures 1 and 2). Cover crops were terminated with a sickle-bar mower (at anthesis/pollen shed for the cereal grain crops, and at 100% bloom for the vetch crop) prior to vegetable planting. Bell peppers, snap beans, and potatoes were planted into the cultivated strips in each cover crop treatment in early June at 30 inch centered row spacing.

Crops were fertilized with granulated chicken manure (Chickity-Doo-Doo, OMRI) (snap beans 44.8 kg N/ha, bell peppers and potatoes 89.7 kg N/ha) (Bussan et al. 2012) in the case of the snap beans, along the entire row, and for potatoes and peppers concentrated in a circle around the plant. Crops were watered in by watering can immediately after planting, and drip irrigation was installed to water as needed throughout the season. Pest and disease control was applied as follows in accordance with Organic Standards. EF400 fungicide/bactericide (active ingredient clove and citrus oils) was applied to potatoes at a concentration of 1 oz/gallon by backpack sprayer on three occasions, two weeks apart, as a preventative measure against late blight. Pyrethrum extract (Pyganic) was applied as needed to control leaf-hopper damage to potatoes, at a concentration of 1 oz/3 gallons with acetic acid used to bring pH to 5.5 per company recommendation applied by backpack sprayer.

Throughout the growing season, weed variety counts and biomass samples were collected. Soil samples were sent to the University of Wisconsin Soil Testing Laboratories for phosphorous, potassium, nitrate and total nitrogen (N) analysis. All biomass samples were harvested into paper bags and dried at 70 degrees for one week.

Soil fertility tests were conducted at the UW Soil and Plant Analysis Lab using their standard techniques, measuring soil total carbon/total nitrogen, inorganic N (NH4 + NO3), phosphorus and potassium pH, EC, CEC + exchangeable cations (Ca, Mg, K, Na), micronutrients (Zn, Mn, Cu, Fe), nitrate-nitrogen and soil organic matter. Soil respiration (measured using the SOLVITA assay (solvita.com) will be measured as an indicator of soil microbiology and soil health.

Peppers were harvested in late August at the green-ripe stage. All peppers from each plot were harvested. All beans from twenty row feet within each plot were harvested when > 80 % of beans are at maturity. Potatoes were harvested in September. All produce was harvested by hand. Produce from each plot was sorted into marketable and non-marketable groups, counted, weighed, and assessed for quality.

Soil and root samples from pepper and bean plants were taken in both cover crop rye plots and control plots to examine soil microbial populations, an indicator of soil health. These samples were taken from both the strip-tilled areas (representing the rhizophere/root zone of the crop) as well as in the no-till/cover cropped areas between the rows. In addition to overall impacts on soil ecology, plant-growth promoting phenotypes of bacteria involved in nutrient-solubilization and cycling, as well as modulation of plant hormones, were specifically examined. Laboratory assays are currently being conducting comparing the frequency with which these phenotypes are expressed between field treatments, vegetable crops, and location relative to the plant roots (bulk soil in proximity to the roots, on the root surface, and colonizing root tissue). Assays being conducted include tests for production of protease and pectate lyase enzymes, production of the potential plant-growth promoting compounds acetion, 2,3-butanediol, indole-acetic acid, and ACC deaminase, ability to solubilize phosphorus, and production of siderophores to bind soluble iron. This research will help to assess whether no-till cover cropping and soil conservation contribute to the presence of beneficial soil bacteria.

Accomplishments/Milestones

Hairy vetch germination and survival through the winter was extremely poor and this treatment was replaced by a straw mulch treatment using straw obtained from off-farm as a positive control. Comparing the 2013 and 2014 biomass, more cover crop biomass was produced in 2013 versus 2014. Across treatments, in 2013, biomass ranged from approximately 1,050 to 1,350 g per meter sq, with wheat producing more biomass than the rye crops (Figure 1). Conversely, in 2014, overall biomass ranged from 850 – 950 g per meter sq., with no significant difference in biomass production between the rye and wheat cover crops (Figure 2). Greater numbers of weeds were found in the wheat mulch as compared to the cereal rye in 2013 (Figure 3). Early season weed density was significantly greater in the control plots than in the rye plots, although later in the season density was comparable (Figure 3). This impacted the in-season labor required for weed management, with wheat plots requiring the most labor and rye plots having management needs similar to the control plots (Figure 4).  Later in the 2013 season, weed densities were more similar among treatments (Figure 5).   Thus, weeding times were more similar among treatments later in the season, although the control plots required, on average, less labor time to manage weeds (Figure 6). In 2014, weed density in the rye plots was less that of the control plots in the early part of the season (Figure 7). However, labor time required for early season weed management was still greater in the rye plots than in the control plots (Figure 8). Similar to 2014, later in the season, weed densities in the rye and control plots were similar (Figure 9), although labor time for weed management was less in the control plots than in the no-till plots (Figure 10).

Pepper plants in the no-till rye plots yielded similarly to the control plots in both 2013 in 2014 (Figure 11). In both seasons, peppers from the wheat plots yielded less than in the rye plots. Pepper yields from the straw mulch plots varied; in 2013, the peppers in the straw mulch had greater yields than the other treatments, while in 2014, peppers from the no-till plots out-yielded the straw mulched plots (Figure 11). Bean yield was greater in the control plot relative to the no-till and mulch treatments (Figure 12). In 2014, weed pressure due to volunteer oats in the straw mulch probably impacted this treatment so as to significantly decrease yield (Figure 12).

Potato yields were not significantly different among treatments in 2013 (Figure 13). Wheat treatments showed a lesser potato yield than the other mulch treatments, although yields were not significantly different than other treatments. In 2014, however, there was a greater yield of potatoes from the control plot (Figure 13). Although weed pressure may be a factor, damage caused by potato leafhoppers and rodents decreased the harvest of marketable potatoes in 2014. There was a greater incidence of loss due to these factors in the mulched plots, probably due to their providing a preferable habitat for pests.

These results suggest the fruitfulness of future work with winter rye as a cover crop, together with other varieties of winter hardy vetch or red clover to add nitrogen fixation to the benefits of this system. Overall, adequate cover crop biomass production was found to be a key factor in determining the extent of weed suppression and productivity of this system. One shortcoming of this experiment was that it only ran for two seasons, in adjacent but different fields, limiting the assessment of long-term impacts on soil health. Given the high weed density both years, we would recommend that farmers manage the initial weed seed bank before attempting this method for long-term weed control. Cooler soil, production of allelopathic compounds by rye, and slower cycling of organic matter from the cover crops to replenish soil nutrients may also impede growth in cover cropped plots. Future research should take into account the impacts of these factors. It would also be helpful to experiment with other vegetable crops.

            One measurement of soil health that we pursued was the assessment of the impact of organic no-till production on soil biology. Our initial bacterial assays do not show a significant difference in enzymatic activity or production of plant-growth promoting compounds between rye and control plots. As expected there is greater incidence of these phenotypes in samples taken from the root surface (the rhizophere) than in the bulk soil. Laboratory work with bacterial samples is ongoing and will be completed by this summer. Impacts of no-till production on mycorrhizal growth, longer term effects, once the organic matter of the cover crops is fully broken down and corroboration with other techniques to measure impacts on the microbial community, would be advisable for future research.

Impacts and Contributions/Outcomes

This research is part of a larger cover crop project that includes on-farm trials at organic farms and is overseen by a 10-member organic farmer advisory panel (including representatives from Troy Community Gardens and the FairShare Community Supported Agriculture Coalition). Initial findings were presented at a 2013 Organic Field Day at the West Madison Agricultural Research Station and incorporated into a larger no-till organic presentation at the 2014 Organic Field Day. Feedback on this research was solicited from farmers interested in utilizing cover-crop based reduced tillage in urban areas at the Growing Power Small and Urban Farmer’s conference in Milwaukee and from several organic vegetable farmers in southeastern Wisconsin. This research was presented at the 2014 American Society of Agronomy-Crop Science Society of America-Soil Science Society of America meetings in Long Beach, CA and discussed with from organic researchers working with these methods within the Organic Management Systems Community. A poster presentation of soil microbiology aspect of this work was presented at the 2014 American Phytopathological Society-Canadian Phytopathological Society meeting in Minneapolis. Although the research was led by Anne Pfeiffer as a core part of her graduate thesis, the support from SARE was further leveraged and incorporated the involvement of a second graduate student, Eric Bietila.

Collaborators: