Kathleen Delate, Extension Organic Specialist, Iowa State University, Ames, IA
Cynthia Cambardella, Soil Scientist, USDA-ARS National Lab for Agriculture and the Environment, Ames, IA
Jeff Moyer, Farm Manager, Rodale Institute, Kutztown, PA
Organic grain production, including soybeans, reached 1,072,107 acres in the United States in 2008 (United States Department of Agriculture [USDA] Economic Research Service [ERS], 2012). The majority of U.S. organic grain is produced in the Midwest, where in 2008 there were 374,302 acres of organic corn and 93,567 acres of organic soybeans.
The majority of organic grain producers in the Midwest rely on tillage operations to manage weeds, using rotary hoes or harrows for over-the-row weed management and row cultivators for between-row management. While tillage operations can be very effective, there has been some concern about the potential negative impact of tillage operations on soil quality–particularly for producers interested in participating in USDA Natural Resource Conservation Service [NRCS] soil conservation cost-share programs that focus on mitigating soil erosion. In order to meet certified organic requirements and enter the expanding organic market, producers must implement a soil-building plan in accordance with sections 205.203 and 205.205 of the National Organic Program (NOP) final rule (USDA, 2000). At the heart of the regulations is the protection or enhancement of carbon and other nutrients in soil organic matter to maintain soil fertility and structure.
Successful weed management is also critical for organic and transitioning farmers. Cover crops serve a dual role of providing fertility and helping to manage weeds. They can be plowed under prior to grain crop planting, or terminated without tillage in reduced tillage or no-till operations.
There is wide acceptance of no-till in conventional production systems that rely on herbicides, but it is still sometimes more difficult to get consistent crop stands in no-till compared to tilled conventional systems because of cold soil and increased insect and disease pressure on emerging seedlings. No-till is even more challenging in organic systems because organic-compliant seed treatments to protect seedlings from insects and diseases are limited, and organic-compliant herbicides are expensive to use on a broad scale and less effective than synthetic herbicides. If weeds emerge through the crushed cover crop mulch, there are limited options; however, high residue cultivation can be used to aid in managing weeds.
This article reports preliminary research findings on no-till organic systems.
Management of soil organic matter (SOM) to enhance soil quality and supply nutrients is a key determinant of successful organic farming. This involves balancing two ecological processes: mineralization of carbon (C) and nitrogen (N) in SOM for short-term crop uptake; and sequestration of C and N in SOM pools for long-term maintenance of soil quality, including structure and fertility.
Using organic amendments, crop rotations, and cover crops are multifunctional management practices that conserve soil organic matter, enhance soil quality, protect soil from erosion, and sequester C to help mitigate global climate change. Nitrogen fertility is maintained through synchronization of N mineralization from soil organic N pools, and plant uptake of inorganic N. Leguminous cover crops provide short-term yield benefits through rapid mineralization of inorganic N from plant biomass. Decomposing cereal grain cover crop biomass immobilizes soil N to reduce N leaching loss during the winter months, and contributes relatively more C as stabilized soil organic matter than legumes. Including small grain and leguminous cover crops in organic rotations may help optimize soil N cycling to enhance productivity and minimize loss of N from the rooting zone.
The intensive tillage that is often used in organic production can compromise soil quality gains, unless more C-rich amendments are added (manure, cover crops, compost, etc.) than are lost through decomposition. Reducing tillage in organic farming systems is a major challenge for producers because of its central role in weed management. The development of effective reduced tillage methods across a range of climates and farming systems is key to improving the environmental and economic sustainability of organic production.
Reduced tillage of cover crops in organic no-till systems has become the goal of many organic producers in the United States. Following the lead of conventional no-till systems, organic producers recognize the benefits of reduced tillage on soil physical, chemical and biological properties. No-till cover crop termination methods developed for organic systems include mowing, stalk-chopping and undercutting—all of which can lead to patchy distribution and rapid breakdown of the mulch—providing more opportunities for weed establishment and growth. Rolling or compressing the cover crop with a no-till roller/crimper can help to uniformly deposit cover crop residue and allow for a more persistent mulch cover throughout the growing season (Creamer and Dabney, 2002; Morse, 2001).
With the support from a USDA Conservation Innovation Grant [CIG], the Rodale Institute (Kutztown, PA) distributed no-till roller/crimpers to several U.S. universities in 2005 to help develop site-specific recommendations for no-till organic production (Hepperly, 2007). The roller consists of a large steel cylinder (10.5 ft wide x 16 in diameter) filled with water to provide 2,000 lbs of weight. Steel blades are welded in a chevron pattern to crimp and mechanically kill fall-planted cover crops in the spring (see Fig. 1). The roller can be rear-mounted or, more ideally, front-mounted on a tractor to crush cover crops and plant crop seeds in a single pass of the tractor. A dense, uniform cover crop is needed to create a mulch capable of suppressing weeds to avoid or greatly reduce the need for additional weed control, such as high-residue cultivation, throughout the season. Corn and soybean seeds can be planted or drilled into the flattened cover crop, using no-till planters or drills. Successful production of organic corn, soybean, tomatoes, pumpkins, and strawberries has been achieved with rolled cover crops in Pennsylvania and Michigan (Sayre, 2005). Visit Rodale Institute's webpage for organic no-till for additional information. Despite several successes, there have been many challenges with the organic no-till system (Carr et al., 2012), particularly with failure of cover crop termination (Delate et al., 2012) and cover crop residue impeding placement of supplemental fertilizers (Mirsky et al., 2012).
Figure 1. Rolling/crimping rye cover crop before planting organic soybeans. Photo credit: Kathleen Delate, Iowa State University.
Organic no-till for corn and soybean production has been studied across the Midwest since 2005. At the Iowa State University Neely-Kinyon Farm in Greenfield, Iowa, cover crop combinations of hairy vetch and rye (HV/R), and Austrian winter pea and winter wheat (AWP/WW), were planted in September through October and killed with a roller/crimper in late May of the following year. Rolling/crimping took place when the rye and wheat covers were at or past anthesis or pollen-shedding, and the vetch and peas were at full bloom. The hairy vetch/rye combination provided superior mulch cover over the wheat/pea mixture due to greater biomass and stand. In the first year of the experiment, organic soybeans yielded 45 bushels/acre in the hairy vetch/rye system—an excellent yield considering no post-planting tillage operations for weed management were employed (Delate et al. 2011).
A six-state (IA, MN, WI, MI, ND and PA) USDA National Institute of Food and Agriculture [NIFA] Organic No-Till Project was initiated in 2008 following a wheat crop planted on plots in all states to create a uniform crop history. Cover crops in the no-till experiment were established in fall 2008 and consisted of the following treatments: 1) a conventionally tilled treatment where cover crops (hairy vetch and rye) were planted in fall and tilled in spring, with tillage used after commercial crop planting for weed management; and 2) a no-till treatment where cover crops were planted in fall and rolled/crimped in spring with no further tillage. Plot size varied across states based on available land, averaging 30 x 100 feet with 4 replications per treatment. In May or June (weather-dependent), cover crops were either disked in the conventional tillage system, or rolled/crimped in a one-pass organic no-till system. Commercial crops of corn (following hairy vetch) and soybean (following rye) were planted with the goal of the crushed cover crops serving as a dried mulch between crop rows throughout the season. Cover crop performance was excellent: rye biomass averaged 8,952 pounds per acre across 5 sites, and hairy vetch biomass averaged 4,118 pounds per acre across 4 sites. All sites experienced some hairy vetch winter-kill, but the northernmost states (MN and ND) reported severe hairy vetch winter-kill, thus making this cover crop of limited use for organic no-till in these states.
The no-till system worked well for soybean in the crushed rye in all states when rye was rolled/crimped at or post-anthesis (see Fig. 2). Organic soybean yields averaged 26 bushels per acre in the first season without any post-planting weed management, compared to 33 bushels per acre in the conventional tillage system, which averaged 3 post-planting weed tillage operations (see Fig. 3).
The no-till corn system was much more challenging. There was only one state (PA) where no-till organic corn yields exceeded 100 bushels per acre. The corn yield average over the remaining sites was only 33 bushels per acre, compared to 73 with conventional tillage. The low corn yields overall were associated with poor overwintering of the hairy vetch cover crop in all states; a wet, cool season; high weed populations; and low nutrient availability, since the corn crop relied solely on N from the hairy vetch with no compost or manure added to the experiment.
In the majority of sites, weeds were greater in the hairy vetch/corn no-till system than the conventional tillage system. Perennial weeds were particularly problematic in the organic no-till system after one full season without tillage. The weed population was not censused prior to planting the cover crop, so it is unknown if previous weed populations aggravated the weed problem. Although weeds appeared to be less of a problem in the early-season no-till soybean plots, presumably from the rye’s thick, weed-free mulch, the rolling/crimping appeared to stimulate reproductive growth of secondary tillers. By the end of the season, the no-till soybean plots had many rye plants between soybean rows. While not critically impacting soybean yield, the presence of the rye plants at the end of 2009 led to interference with the growth of the oat crop that followed soybean in the rotation in 2010. Oats were no-till drilled, in keeping with the no-till protocol of the long-term experiment.
Figure 2. View of rolled/crimped rye cover crop with soybeans planted in one-pass operation. Photo credit: Kathleen Delate, Iowa State University.
Lower yields in no-till oat plots were associated with perennial weeds such as Canada thistle, dandelion, quackgrass and clovers; and resurgence of previously planted hairy vetch and rye cover crops. Because of the high weed populations, plots were tilled at the end of the second year after two crop-years of no-till corn or soybean followed by no-till oats, before drilling cover crops for the second no-till phase. In the second no-till corn and soybean phase, despite similar corn plant populations (no-till: 25,690 plants per acre; conventional tillage: 24,904 plants per acre), no-till corn yields again disappointed cooperators, with no-till yields only 37% of conventional tillage yields. These results strongly suggest that Midwest conditions are not conducive to successful organic no-till corn with hairy vetch as the sole source of N. Soybean plant populations in the second no-till season were 4,000 plants per acre less than in the conventional tillage system, but yields did not suffer. Cold, wet weather led to slow germination of seed, but similar yields were obtained in no-till and conventional tillage organic soybean fields, averaging 25 bushels per acre across 5 sites. Broadleaf weed populations were much greater in no-till fields, but annual and perennial grass weeds were not as high in oat, corn and soybean fields, suggesting that these crops are reasonably competitive with grass weeds in the no-till system. Despite high weed populations, no-till soybean yields were competitive, suggesting excellent compensatory function from high planting populations and extensive pod set.
Figure 3. Close-up of organic soybeans emerging in rolled/crimped rye cover crop. Photo credit: Erin Silva, University of Wisconsin-Madison.
Prior to cash crop planting at the beginning of the Organic No-Till project, soil quality analysis revealed no significant differences in any parameters between the no-till and the conventional tillage fields. After 3 years of no-till, soil microbial biomass carbon (MBC) values were significantly greater in no-till than in conventional tillage plots at 4 of the 5 relatively moist sites located in the upper and central Midwest, and PA. In ND, where rainfall was only 17 inches per year, MBC did not increase in no-till plots (Table 1). These findings could be explained by noting that MBC quickly reacts to soil management changes as experienced with the no-till treatment, since reduced soil disturbance from no-till and higher available C concentration in the top soil layer has been shown to lead to increased microbial populations. In addition, higher microbial biomass content is generally considered an indicator of soil fertility, despite lower yields in the no-till treatment.
|No-till (NT)||Conventional-till (CT)|
|North Dakota||96||116||Signif. greater in CT|
* Significantly greater at <0.10. ** Significantly greater at <0.05.
At 3 sites (IA, MI, and MN), residual soil nitrate-N, pH, and electrical conductivity were greater under no-till than conventional tillage. At only one of 6 sites (IA), bulk density was higher and macroaggregation lower under no-till, suggesting increased soil compaction. However, bulk density was not significantly different at half of the sites, and was significantly higher under conventional tillage at 2 sites (MN and PA), indicating that no-till management had differential effects on soil compaction for the sites under investigation. Total soil N and potentially mineralizable N were higher under no-till at the WI research station site, demonstrating enhanced cycling and storage of soil N. Because soil quality changes take multiple years to document, further research is needed to verify possible changes induced by the different soil management and crop rotation strategies.
Average returns to management for organic corn, oats and soybean were greater in the conventional tillage system compared to the no-till system in all years, across all sites. The potential for reduced fuel, equipment, and labor costs with no-till will encourage more organic no-till systems if production challenges can be overcome. In addition, if benefits from soil C enhancement and greenhouse gas reduction were included in the analysis of no-till systems, the economic and environmental picture would be brighter for organic systems (Singerman et al., 2011).
Regional differences and site-specific recommendations for organic no-till grain production will continue to be investigated across the Midwest. Growers should only try the no-till system on a small scale for several years to get experience under varying conditions before committing sizable acreage. Organic no-till soybeans have been shown to have more stable yields than no-till corn, so farmers interested in experimenting with this system should try soybeans first. It is important to note that weather plays a key role in the effectiveness of the organic no-till system—adequate moisture is needed for the commercial crop to compete with the cover crop, particularly if any cover crop regrowth occurs. Adding irrigation in dry years could dramatically improve the performance of these systems in semi-arid locations. On the other hand, late spring rains can delay rolling/crimping of the cover crop and delay planting or maturity of the commercial crop, thus leading to a lower yield. As with any new technology, several challenges remain. The goal of reducing tillage in organic systems to ameliorate C losses and reduce petroleum costs in weed management, however, propels this research forward.
This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.