Iowa State Study Shows Soil-Building Benefits of Organic Practices

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Organic agriculture also promotes practices such as extended crop rotations and soil amendments including animal manure and compost.

Reposted with permission from theLeopold Center for Sustainable Agriculture.

Producers making the switch to organic crops to meet growing market demand not only fetch premium prices, according to a recent study; they also build healthy soil and sequester carbon, making organic agriculture a useful strategy for dealing with climate change.

The study, published in Crop Management in April, summarizes results from the Long-Term Agroecological Research (LTAR) Experiment, one of the longest running replicated comparisons of organic and conventional agriculture in the country. The experiment began in 1998 with funding from the Leopold Center for Sustainable Agriculture. The LTAR site also has been used as a demonstration plot for U.S. Department of Agriculture studies.

“Farmers interested in transitioning to organic production will be happy to see that, with good management, yields can be the same, with potentially higher returns and better soil quality,” said Kathleen Delate, agronomy and horticulture professor at Iowa State University, who leads the project.

Organic food sales have tripled in the U.S. over the last decade. To market a crop as organic, it must be grown on land that has received no synthetic chemicals for three years prior to harvest.

Organic agriculture also promotes practices such as extended crop rotations and soil amendments including animal manure and compost. Although organic practices are not the only way to improve soil health, the ISU experiment showed that some of the biggest changes over time were in soil quality, particularly once the system was established.

Delate’s study found that soils in the organic plots (three- and four-year rotations of corn, soybean, oats and alfalfa) had significantly higher quality compared to the plots using a conventional two-year rotation of corn and soybeans. The organic plots had up to 40 percent more biologically-active soil organic matter, which is important for fertility and nutrient availability. Organic soils also had lower acidity and higher amounts of carbon, nitrogen, potassium, phosphorous and calcium.

Healthy soils also hold more water and improve water infiltration, increasing a farm’s resiliency to drought, heavy rainfall and extreme weather events. Farming practices that build soil health also increase carbon storage in soil, called carbon sequestration, which buffers climate change and contributes to better water quality.

The LTAR experiment is located on 17 acres at the ISU Neely-Kinyon Research and Demonstration Farm near Greenfield. The project compares four crop rotations using identical varieties that are repeated four times in 44 plots. The conventional rotation received synthetic nitrogen, herbicides and insecticides according to ISU recommended rates. The organic corn plots received composted manure from a local chicken operation. Weeds are managed by timely tillage, longer crop rotations, cover crops and allelopathic chemicals from rye and alfalfa.

Project investigators also gathered data on yields and economic viability, with promising results. Corn and soybean yields were statistically equivalent in the organic and conventional systems during both the transitional phase (1998-2001) and established phase (2002-2010) of the experiment. Yields for organic oats and alfalfa exceeded county averages.

Based on plot-level data, the economic analysis showed that the organic crops fetched roughly $200 more per acre over the 13 years of the study because of premium market prices and reduced input costs. In 2010, for example, an acre of land planted with the four-year organic rotation returned $510, while an acre planted with conventional corn-soybean returned $351.

On average, labor requirements doubled for the organic systems. There was no significant difference in the number of crop pests. The results suggest that skilled management practices can overcome the need for synthetic inputs.

“Soil health is critical to any agricultural production system, and organic practices are among many ways to improve the health of our soils,” said Leopold Center Director Mark Rasmussen. “We hope that what we are learning from the LTAR experiment can be applied to other production models.”

The article can be found in the peer-reviewed journal Crop Management and is titled, “The Long-Term Agroecological Research (LTAR) Experiment supports organic yields, soil quality and economic performance in Iowa.”  Details about the project are available on the Leopold Center website. Information about related research can be found on the ISU Organic Agriculture website.

Delate’s co-authors were Cynthia Cambardella, USDA Agricultural Research Service; Craig Chase, Leopold Center Marketing and Food Systems Initiative; and Ann Johanns and Robert Turnbull, ISU Extension and Outreach.