Cropping Systems Research Team

red clover in fieldCombine in field

Extending the conventional corn-soybean rotation with small grains and forages, such as clover and alfalfa, can reduce requirements for purchased inputs and petrochemical energy. An interdisciplinary team of researchers, from several ISU departments, the USDA Agricultural Research Service, the University of Minnesota and the University of Illinois, is conducting an experiment to compare the performance of two-, three- and four-year crop rotation systems.

The overall objective is to develop diversified crop rotations that will help maintain yields, minimize requirements for synthetic fertilizers and herbicides, reduce production costs, maintain or increase net returns, and protect environmental quality. The experiment began in 2002 at the ISU Marsden Farm in Boone County, Iowa. 

The goals of the Cropping Systems Research Team:

  • Study the agronomic, ecological and economic effects of conventional and high-diversity-low-input cropping systems, including:
    • Soil organic matter and fertility
    • Labor requirements, input costs and net returns
    • Fossil energy use
    • Weed and disease dynamics
  • Compare the performance of transgenic and non-transgenic corn hybrids and soybean varieties within the contrasting rotation systems

The cropping systems studied are:

  • Conventional corn-soybean (2 year)
  • Corn-soybean-small grain/red clover (3 year)
  • Corn-soybean-small grain/alfalfa-alfalfa (4 year)

Latest findings - 2015

The latest findings from this research continue to be positive: diversifying the crop system and integrating livestock consistently boost productivity, profitability and environmental health. The updated findings reflect data from 2006 through 2014. The project baseline was 2001-2002, with a 2003-2005 start-up period.

  • SOIL HEALTH IMPROVES. Soil managed with the longer rotations (3- and 4-year vs. 2-year) has more particulate organic matter carbon, more microbial biomass, and greater ability to release nitrogen from organic matter.

  • FOSSIL ENERGY USE FALLS. There is a 59 percent reduction in fossil fuel use for 3- and 4-year rotations as compared to 2-year rotation.

  • EROSION POTENTIAL IS REDUCED. Estimated sheet and rill erosion (tons/acre/yr) falls from 1.36 in 2-year rotation system to 1.08 and 0.88 in the 3- and 4-year systems, respectively.

  • YIELDS REMAIN STRONG. Corn and soybean yields remain statistically higher in the 3- and 4-year rotations than in 2-year rotation.

  • WEEDS REQUIRE MANAGEMENT but have not been a problem. Low weed pressure has been seen in all phases of all rotations over years, with relatively greater weed growth in oat and alfalfa phases than the corn and soybean phases.

  • PROFITABILITY IS ACHIEVED. Returns to land and management, 2008-2014, are $384, $409, and $413 per acre for 2-, 3- and 4-year rotations, respectively.

  • HERBICIDE AND N FERTILIZER USES ARE DRAMATICALLY REDUCED. The 3- and 4-year rotations are using 88 percent and 92 percent less mineral N-fertilizer and 96 percent and 97 percent less herbicide.

  • REDUCED DISEASE SUSCEPTIBILITY. The 3- and 4-year rotations continue to exhibit highly statistically significant reductions in the incidence and severity of soybean sudden death syndrome.

    A new research component, water pollution,  was added to this project. Data are being analyzed with the USEtx model for herbicide-related toxicity, which is reported in comparative toxic units per hectare per year. Aquatic herbicide-related toxicity potential is dramatically reduced from 10,974 units with the 2-year rotation to 33 and 24 units with the 3- and 4-year rotations, respectively.




This project has been funded by the Leopold Center for Sustainable Agriculture, U.S. Department of Agriculture National Research Initiative, Iowa Soybean Association, and The Organic Center.