The demand for organic grains is increasing. Farmers making the transition to organic production cite weed management as their biggest challenge. The objective of the project was to determine if an organic no-till system was feasible in the Southeast US. Experiments were held throughout the state. A rye (Secale cereal) cover crop (‘Rymin’) was planted in late fall and rolled/crimped or flail-mowed prior to planting to create a weed suppressing mulch with potential allelopathic properties. To augment weed control, one pre-emergence and two post-emergence weed management tactics were evaluated. Compared with conventionally treated check plots, the rolled rye system resulted in equivalent soybean yields at most of our locations. Rye biomass levels played a critical role in weed suppression.
In a separate experiment, we planted 14 legume cover crop varieties, including berseem clover, subterranean clover, sweet clover, crimson clover, hairy vetch, common vetch, winter pea and blue lupine, and we planted 6 varieties of rye. Cover crop stands have been evaluated, and all the legume cover crops have been rolled on two to three different dates from early April to early May in order to see how rolling and planting match up with full-bloom for cover crop kill. Corn was no-till planted into the rolled cover crops.
Demand for organic corn and soybeans in North Carolina is growing. Braswell Milling in Nashville, NC estimates they need at least 500,000 bushels of organic corn and 7,000 tons of organic soybean meal each year to supply their organic egg farms. A group of farmers in eastern North Carolina have incorporated as Eastern Carolina Soy Products, LLC to build a soybean crusher that will process up to 400,000 bushels of organic soybeans each year. Although demand for organic grains is high, NC producers cannot take advantage of these opportunities. North Carolina currently imports a majority of its organic corn and soybeans to meet market demand. Weed management in organic soybeans and adequate fertility for organic corn are the biggest challenges in developing a sustainable organic grains rotation system.
Currently, weed management in organic soybean production relies heavily upon multiple secondary tillage passes over the field each season. Increased tillage can result in increased soil erosion (Beale et al., 1955) and soil compaction (Raper et al., 2000), increased fossil fuel requirements (Hargrove, 1990), increased CO2 release (Paustian et al., 1998), increased labor costs (Weersink et al., 1992), increased equipment costs (Weersink et al., 1992) and decreased soil residue cover (Hargrove, 1990).
Some cover crops such as rye have demonstrated allelopathic (releases weed inhibiting chemicals) properties (Barnes et al., 1987). A newly designed chevron roller can be utilized to effectively kill the rye and create a thick biomass layer on the soil surface. By planting soybeans into such a biomass layer, weed growth can be greatly inhibited. This system has been successful at the Rodale Institute in the Northeast, but it has not been investigated for the Southeast region. With the increased research and development of organically certified herbicides (Tworkoski, 2002), use of corn gluten (shown to possess weed suppressive qualities (Christians 1993)) and high residue cultivation equipment (Paarlberg et al., 1998), more options have become available to successfully implement no-till organic grain production.
Many farmers interested in organic grain production farm in NC’s Tidewater region; an area of poorly drained, high organic matter soils. Most organic grain farmers in the state would like a cover crop to contribute significantly to the nitrogen budget of their corn crop. In organic systems, reliance on manures for nitrogen isn’t sustainable due to increasing phosphorus levels and concerns of environmental contamination (Bulter et al., 2005). Crimson clover is typically recommended for adding large amounts of biomass with high nitrogen content. However, crimson clover is inhibited on poorly drained soils (Yenish et al., 1996; Cavigelli et al., 2007). Hairy vetch is also a significant contributor of nitrogen and known to tolerate wet soils (Anderson et al., 1990). In an attempt to incorporate no-till into a full rotation system, farmers have identified the need to further investigate the limitations of crimson clover on poorly drained soils and the potential use of hairy vetch, a cover crop more tolerant to wet soils but rarely used in North Carolina grain rotations.
We utilized research stations and on farm trials to compare no-till organic soybean systems utilizing different combinations of the following tactics: planting soybeans into a rye cover crop compared to planting into no cover crop; planting soybeans into a rolled down rye cover crop compared to planting into an undercut rye cover crop; planting soy with a 7 inch band of corn gluten over the crop row, use of post crop emergence clove oil organic herbicides with sprays directed under crop foliage and the use of one pass of a high residue cultivator to control weeds between crop rows.
We also proposed a multi-location investigation of nitrogen contribution by crimson clover and hairy vetch cover crops grown on poorly drained soils preceding corn as part of the no-till organic grain rotation.
Wade and Daren Hubers’s farm in Hyde County, NC grows approximately 1500 acres of corn and soybean, with 200 acres managed organically. Wade and Daren Hubers have allocated several acres for this on farm trial to be planted. Rye will be sown in October 2007 at seeding rates of 1.5 bushels/acre. Some rye plots will be mowed in mid March to reduce biomass and allow for a high and low rye biomass comparison. Treatments beginning with the roll down or undercutting of rye plots will take place in mid to late April, prior to planting full season soybeans. Comparing rolled down rye and undercut rye will facilitate assessment of rye kill effectiveness and the effect on weed suppressive ability of the rye. Soybeans will be planted into differing treatments in late April to early May with some soybean plots including the spreading of a 7 inch wide band of corn gluten, a potential pre-emergence organic herbicide, over the soybean row. Organically labeled vinegar herbicides will be spray-directed under crop foliage 1-2 weeks after soy planting in some plots. A high residue, minimal soil disturbance cultivation pass will occur 4-5 weeks after soy planting to kill weeds between soybean rows before the closure of the soybean canopy. These treatments were identified priorities for investigation by organic grain farmers, NCSU researchers dedicated to the area, and the Hyde county extension agent who has many farmer clients interested in organic grain production.
During the season, the following data measurements will be taken:
Soil temperature (at soybean planting and 3-4 weeks after planting (WAP))
Soil moisture (at soybean planting and 3-4 WAP)
Biomass levels of rye (at soybean planting and 3-4 WAP)
Weed count (at soybean planting and 3-4 WAP)
Weed distribution (at soybean planting and 3-4 WAP)
Rye kill percentages (3-4 WAP)
Soybean stand count (3-4 WAP)
Weed count and overall plot rating (6-7 WAP)
Yield (November 2008)
We will establish three demonstration sites at farms and three at research stations in distinct geographic regions of the state, including the Coastal Plain, the Blacklands region, and the Piedmont. Besides their geographic distribution, the three farmers are known as leaders in their communities. At each on-farm site, we will help the farmers establish winter cover crops of rye, barley, vetch, and crimson clover. Multiple cultivars of each species will be planted that will provide for an array of flowering times. We will roll the cover crops and plant corn and soybeans at the appropriate time for each region. Some of the legume cultivars will not have flowered yet while others will. We will evaluate the cover crop stands, effectiveness of roll-killing the cover crop, and the cover they provide as mulch to the grain crop. Farmers attending field days will be able to see the effect of these differences in flowering time on how well the cover crop is killed.
The use of rye cover crops for weed suppression was successful. Rolled rye resulted in pigweed (Amaranthus retroflexus L.) cover of 3% vs. 13% in flail-mowed rye. Corn gluten meal increased weed coverage at most locations and reduced yield by 208 kg ha-1 on average across locations. Compared with conventionally treated check plots, the rolled rye system resulted in equivalent soybean yields at Goldsboro and Plymouth where biomass was 10854 kg ha-1 and 9526 kg ha-1, respectively. Additionally, rolled rye in combination with clove oil resulted in slightly higher soybean yields than conventional check plots at both sites. In Kinston, a low rye biomass of 6606 kg ha-1 was insufficient for adequate weed control and soybeans from rolled rye plots yielded 853 kg ha-1 less than those from conventional plots. Rye biomass levels played a critical role in weed suppression.
We held a workshop on February 27, 2009 in Rocky Mount, NC where this project was discussed and Dr. Julie Grossman gave a lecture using cover crops practically in organic production systems. Over 50 people were in attendance.
Six varieties of rye were rolled on 2 roll dates (mid-May and late-May). Soybeans (NC Roy, maturity group 6) were immediately planted into the rolled rye. Regardless of roll date, all rye varieties were killed successfully. Soybeans emerged well from the rye mulches, and weeds were slow to break through. As of early September, pod set at both research station sites looked great. Weed control was implemented in soybeans at each research station and consisted of trialing organic herbicides (corn gluten meal and clove oil) cultivation, and rolled rye mulch alone. The rolled rye mulch alone controlled weeds very well, though at some sites, cultivation or the organic herbicides also performed well.
Only the crimson clover varieties and two hairy vetch varieties were killed during the 2nd and 3rd roll dates (early May and mid-May). Corn was immediately planted into the rolled legumes. Corn was harvested by hand in September and yield data is still being analyzed.
Three on-farm workshops were held on May 7, May 28, and June 4th, 2009 in Mt. Ulla, Tyner, and Pantego, NC respectively. A total of 45 farmers, Extension personnel, and crop advisors attended the three workshops. At the workshops, attendees saw the roll-crimper in action, as well as corn emerging in the killed and not-killed legume cover crops. They saw the rye rolled and learned how to tell if a variety is in full bloom (and therefore susceptible to roll-killing). All attendees found the workshops useful and many said they plan to try some aspect of cover cropping and the no-till/roll-kill technique.
Updates on the progress of the roll-kill/no-till demonstration project were written up and sent in our e-newsletter to over 225 farmers, Extension personnel, NRCS personnel, and other farm advisors in June and September.
We also developed a chart on the full bloom (roll-kill) timing for each legume and rye variety that should be useful to farmers and advisors. It was included in our June 2009 e-newsletter. A special session on the project was held during the Organic Field Crops Conference on Jan. 15th 2010.
Two manuscripts have been developed from the project are being submitted now to academic journals. A bulletin on no-till organic soybean production will be published this summer. The legume/corn part of the project is continuing with funding from the Natural Resource Conservation Service and will be published after 2010 data comes in. We will track farmer use of all materials and workshops to determine the level of impact on farmer practices.