Combining Alternative Cover Crop Strips, Living Mulches and Strip Tillage for Effective Weed and Nutrient Management in Organic Sweet Corn Production

Combining Alternative Cover Crop Strips, Living Mulches and Strip Tillage for Effective Weed and Nutrient Management in Organic Sweet Corn Production

Summary

Despite the benefits of reduced tillage for fuel savings and soil health, adoption by organic farmers has been limited due in part to the challenges created for weed management. The objective of our proposed research was to improve weed suppression and nutrient management in organic vegetable production by using a novel approach of alternating cover crop strips in strip-tillage systems. In the first year of the study we tested various cover crop spatial arrangements in combination with strip-tillage. N-fixing hairy vetch (Vicia villosa Roth) was planted in a strip directly in-line with future sweet corn rows (IR) to supply N directly to the crop. This was compared to the standard practice of planting vetch across the whole plot. Cereal rye (Secale cereale L.) was planted between crop rows and mowed and left on the soil surface to provide a mulch for weed suppression. Additionally, white clover (Trifolium repens L.)was frost-seeded in the between-row area to act as a living mulch for additional weed suppression and increased N. We found that while white clover emergence in the spring was high, cereal rye suppression of the white clover living mulch resulted in little white clover survival into the summer. In the first year we did not see any significant differences due to hairy vetch arrangement, most likely due to poor vetch biomass. In the second year we excluded the white clover living mulch to further examine how cereal rye and hairy vetch spatial arrangement impacts cover crop growth, as well as soil N, weeds, and sweet corn yields. Treatments in the second year consisted of tillage (conventional vs. strip till), cover crop spatial arrangement (segregated vs. mixed), and weed management (high vs. low). We found reduced emergence of both common lambsquarters and giant foxtail, as well as reduced weed biomass, in the between row of zone tilled treatments. Under high weed management, we did not see significant differences in yields based on cover crop spatial arrangement or tillage. However, in zone-tilled treatments(regardless of cover crop spatial arrangement) we had reduced yield loss due to low weed management when compared to conventional tillage. Our results indicate zonal tillage used in combination with stripped intercropping of cover crops may be an effective strategy to adapt reduced tillage systems to organic vegetable production.

N deficiency and weed competition are the two greatest limitations to achieving maximum yields in organic systems. Increasing the synchrony between soil nitrogen (N) availability and crop demand could potentially decrease fertilizer costs, N losses to the environment, as well as weed emergence and vigor.

The goal of this project is to evaluate whether tillage and organic nutrient amendments can be more effectively utilized to improve N and weed management in organic vegetable systems through a combination of segregated cover crop strips and strip tillage. Strip-tillage is a form of conservation tillage that isolates soil tillage to narrow strips directly in row with crop establishment. Tillage in the in-row strip incorporates residue to supply rapid nutrient release, a fine seedbed, and rooting environment beneficial to crop establishment.

Cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) are commonly used winter cover crops in northern climates, often planted in a uniform mixture. An alternative to this planting arrangement is a stripped intercropping of rye and vetch: with vetch planted in strips directly in line with future sweet corn rows (IR) and rye planted in the between row zone (BR). When combined with strip tillage, the N supplying vetch is incorporated prior to sweet corn planting, and we hypothesized we would see greater sweet corn N
uptake due to the concentration of the N rich vetch residue within the sweet corn rooting zone. Additionally, by planting hairy vetch within the IR and incorporating it with strip tillage we attempted to reduce the potential for hairy vetch reemergence as weed during the cropping season. Rye residue planted in the between-row area was mowed and left on the soil surface to immobilize N, and decrease N and light available to stimulate weed emergence. We also proposed combining cereal rye and hairy vetch segregated strips with a white clover living mulch to provide N and additional weed suppression during the sweet corn growing season.

Objectives/Performance Targets

The objectives of this project were to evaluate the effect of vetch and rye alternating strips and strip-tillage on:
1. Weed suppression and community composition within the in- and between-row environments.
2. Cover crop contribution of N and soil N-dynamics.
3. Yield and quality of organic sweet corn.
4. Soil quality by utilizing short-term indicators of changes in soil health.

In summer 2011, we conducted a preliminary trial looking at the effects of segregating rye and hairy vetch into strips, along with frost seeding a white clover living mulch into cereal rye, on sweet corn yield, weed emergence, and N dynamics. Treatments were arranged in a randomized complete block design and consisted of various cover crop spatial arrangements combined with strip tillage, cover crop spatial arrangements included:

1. IR- None, BR- Cereal rye
2. IR-None, BR- Cereal rye + White clover
3. IR-Hairy vetch, BR- Cereal rye
4. IR Hairy vetch, BR- Cereal rye + Hairy vetch

We used the information gathered from the 2010-2011 preliminary trial to further examine how cereal rye and hairy vetch spatial arrangement impacts cover crop growth, as well as soil N, weeds, and sweet corn
yields. Treatments were organized in a split-split plot randomized complete block design with four replicates. Main plots were tillage (conventional vs. strip till), split plot was cover crop spatial arrangement(segregated vs. mixed), and split-split plot was weed management (high vs. low). Segregated cover crop strips consisted of two rows of rye and two rows of hairy vetch (row spacing 7.5 inches) and was compared to the traditional practice of seeding a uniform mixed biculture of rye and hairy vetch. In both cover crop treatments we used the same overall seeding rate: rye was seeded at 56 lbs/acre and hairy vetch was planted at 22 lbs/acre. High weed management subplots were hand-weeded approximately weekly, while low weed management subplots were weeded only twice over the whole growing season. Variable examined included N availability, weed emergence and biomass, and sweet corn yields. To monitor N availability over the course of the summer, soil samples were taken approximately every 10-14 days, dried, ground, and a KCl extraction was performed to measure inorganic N. Seeds of common lambsquarters (Chenopodium album) were broadcasted over low weed management subplots to increase
uniformity of the seedbank. Lambsquarters emergence was counted over the summer, and biomass was collected at three time points: right before each of the two weeding events, as well as at harvest.

Accomplishments/Milestones

In spring 2011 we frost seeded clover into cereal rye within the BR zone. White clover emergence in the spring was high, but cereal rye suppression of the white clover living mulch resulted in little white clover survival into the summer. After the first year resulting in little clover survival, we abandoned this idea and decided to just focus our efforts on examining the rye and vetch system.

Due to poor vetch biomass production in the 2010-2011 preliminary trial, we did not see significant differences in N availability or yields of sweet corn when vetch was segregated within the IR,compared to seeded across the entire plot. We also did not see significant differences in emergence of either commonlambsquarters or giant foxtail. However, we were successful at terminating both the rye and hairy vetch cover crops by mowing. Additionally, not seeding rye within the IR zone increased strip tillage performance by removing the heavy rye residue and dense roots from the tillage zone. N availability was much higher in the IR of all ST treatments compared to the BR, we speculate this difference may have been enhanced by the lack of rye residue and N immobilization in the IR.

In 2012, we saw no statistically significant differences in hairy vetch biomass due to cover crop spatial arrangement. We also did not see significant differences in yields regardless of tillage (strip or
conventional) or cover crop spatial arrangement (mixed or segregated). We found reduced emergence of both common lambsquarters and giant foxtail, as well as reduced weed biomass, in the between row of zone tilled treatments. Under high weed management, we did not see significant differences in yields based on cover crop spatial arrangement or tillage. However, in zone-tilled treatments (regardless of covercrop spatial arrangement) we had reduced yield loss under low weed management when compared to conventional tillage. While we have yet to analyze all of our N data from 2012, it is possible that cover crop lodging may have affected potential N differences between the IR and BR.

Impacts and Contributions/Outcomes

Our results from both 2011 and 2012 suggest that segregating cover crops into strips may be a viable option to address some of the challenges of cover crops and reduced tillage in organic systems, such as reducing cereal rye N tie up and interference with crop establishment. Results in 2012 have shown that hairy vetch can produce sufficient biomass and N to meet crop demand when segregated in cover crop strips. Additionally, we found that strip tillage in combination with a cover crop mulch can effectively reduce weed competition, as well as reduce time spent on weed management.

Results of this research were presented at: 1) an organic farmer field day at the Kellogg Biological Station in 2012, 2) the organic session at the 2012 Great Lakes Fruit and Vegetable Expo, 3) the 2013 Midwest
Organic and Sustainable Education Service, and 4) the 2013 Michigan Organic Poster Session

Prior to advocating for farmer adoption of strip tillage and stripped intercropping of cover crops, there are a few existing challenges that need to be addressed. First, there is a lack of reduced tillage equipment capable of being adapted to diverse small-scale vegetable farms. For example, many small-diversified vegetable growers are planting on a wide range of row spacing and it is uneconomical to purchase equipment on a fixed row spacing like a strip-tiller. To address this challenge we are currently attempting to identify reduced tillage equipment suitable for farms of multiple scales. Second, the high residue mulch can make cultivation required to control escaped weeds difficult, so we are currently testing new high residue cultivation methods for control of escaped weeds.

Future research will examine differences in crop N uptake, as well as N movement through the cropping system by looking at how tillage and cover crop placement effect N mineralization, leaching, and denitrification. We plan on conducting two more years of this study and hope to gain new insight on how to manage cover crops to reduce lodging and maximize the benefit of segregated cover crop strips. We also plan on expanding outreach to farmers in order to gain greater insight on how to tailor reduced tillage for organic vegetable growers

Daniel Brainard
Assistant Professor
Michigan State University- Horticulture
A440-A Plant & Soil Sciences Building
East Lansing, MI 48824
(517)355-5191
E-mail:brainar9@msu.edu
Website: http://www.hrt.msu.edu/daniel-brainard/

Collaborators: