Research at Iowa State University shows how no-till works in organic system
By Kathleen Delate, Iowa State University
No-till or reduced tillage has been proven to provide multiple environmental benefits on conventional farms, particularly in the area of soil conservation. The practice also reduces costs associated with machinery, labor and fuel. On organic farms, no-tillage systems had been constrained by the prohibition of herbicides to terminate cover crops. To overcome this barrier, the Rodale Institute began investigating using a roller/crimper to crush cover crops in lieu of herbicide termination to fit within organic rules. This roller/crimper can be purchased or manufactured using plans published online at rodaleinstitute.org/our-work/organic-no-till/no-till-rollercrimper-plans.
In 2006, the Rodale Institute invited Iowa State University (ISU) to join a consortium with Rodale and UC-Davis, Michigan State (MSU), University of Georgia and Virginia Tech to participate in the first multi-state research on no-till systems for organic farming. As a member of the USDA-NRCS Conservation Innovation Grant for No-Till for Organic Systems (“No-Till Plus”), I conducted the first research on organic no-till systems in Iowa that year.
Our results were encouraging enough to warrant an expansion of this research in 2008 through a consortium of six institutions (ISU, Rodale, MSU, University of Wisconsin (UW), University of Minnesota, North Dakota State University (NDSU), funded by the USDA-NRI Integrated Organic Program.
In 2010, another project was funded with the University of Florida on organic no-till vegetable systems by the NIFA-Organic Transitions Program. ISU also participated in a USDA-SARE project, Organic Corn in No-Till Systems, in partnership with NDSU (Pat Carr) and UW (Erin Silva) to examine the effect of five cover crops on organic corn production.
We planted legume-based cover crops (e.g., hairy vetch and field pea) before high-nitrogen-demanding crops, like corn and vegetables, and rye before soybeans. In warmer climates (Florida, for example), sunn hemp was used as the cover crop.
We have learned an incredible amount from these studies, including the importance of weather conditions when practicing organic no-till. When spring and summer rains fall evenly and adequately, as they did in 2009, organic no-till soybean yields ranged from 37 to 45 bushels per acre, which is an excellent organic tofu-variety soybean yield, especially when you consider no post-planting tillage was performed to manage weeds.
Francis Thicke, organic farmer in Fairfield, Iowa, drilled his organic no-till soybeans on 7–inch rows this year, as opposed to our 30–inch rows. He is expecting over 40 bushels per acre with no weed management. Our concern had been that, by moving to 7–inch rows, we could not perform any “rescue” cultivating if needed. However, based on Thicke’s experience, we are ready to try 7–inch rows next year.
Yields in the organic no-till vegetable systems we have studied in Iowa (broccoli, tomatoes, peppers and lettuce) have been competitive with conventional yields when sufficient biomass is produced by the cover crop, and moisture levels are kept adequate through irrigation. We’ve found that planting the cover crop at 1.5 to 2 bu/acre is best. Sweet corn, however, performs best in tilled systems, which is what we found for field corn, too.
Ideal results occur when the cover crop can be crushed early in the spring (before May 15) when the rye reaches, or is past, anthesis (pollen shed). This timing has become more difficult in recent years with global climate change creating cooler, wetter springs, slowing cover crop growth.
Cindy Cambardella, Soil Scientist at USDA-ARS, Ames, Iowa, has documented increases in soil carbon and microbial biomass carbon and nitrogen in the organic no-till system compared to the normal, tilled organic system. The challenge remains to balance improving soil quality with maintaining optimal yields. Cambardella has found some interesting results, too, with the no-till organic systems sequestering more soil carbon than tilled plots. Nitrate leaching is also reduced in the cover crop-based systems compared to completely tilled plots.
We have found that the vegetable systems are more amenable to organic no-till compared to row crops, due to our ability to use drip irrigation during the crucial period when cover crops are decomposing and the cash crop needs additional moisture. In Florida’s sandy soils, no-till summer squash yields were equal or greater than tilled yields. We saw no significant difference between no-till and plastic mulch, which is phenomenal, when you consider how much additional savings Floridians could obtain by not using plastic mulch.
Organic no-till holds the most promise in warmer climates because of the potential for early cover crop planting, continuous cover crop growth over the winter months, and earlier termination dates in the spring. Sandier soils also seem to be more amenable to organic no-till, as has been demonstrated in both Florida and Pennsylvania, where even no-till corn yields were high. A mechanical issue (e.g., the ability of the roller/crimper to sink deeper into the soil and crush the cover crop that much better) may be a factor here.
Kathleen Delate is a professor of organic agriculture at Iowa State University, and directs the Organic Agriculture Program there.
From the November | December 2015 Issue