Project ID



Balancing productivity, profitability, and environmental health is a key challenge for agricultural sustainability. Most crop production systems in the United States are characterized by low species and management diversity, high use of agrichemicals, and large negative impacts on the environment. We hypothesized that cropping system diversification could allow for large reductions in synthetic external inputs used to maintain crop productivity, including herbicides used for weed control. To test this, we conducted a field study from 2008-2016 in central Iowa that included three contrasting rotation systems: a 2-year corn-soybean system, a 3-year corn-soybean-oat with red clover system, and a 4-year corn soybean- oat with alfalfa-alfalfa system. Each rotation system was managed with conventional and low herbicide regimes.

Key Question

Can cropping system diversification allow for reductions in herbicide used for weed control?


Herbicide inputs in the 3-year and 4-year systems were 33% and 50% lower, respectively, compared with the 2-year system, and, averaged over rotations, the low regime received 88% less herbicide than the conventional regime. Corn yield averaged 4% higher and soybean yield averaged 25% higher in the more diverse systems compared with the 2-year system. Net returns to land and management during 2008–2016 were unaffected by rotation system or herbicide regime. Herbicide-related freshwater toxicity loads during 2008-2015 decreased up to 50% as rotation length increased and were 94% lower with the low herbicide regime than with the conventional regime. Soil erosion and P and N discharges in runoff water were unaffected by herbicide regime, but were reduced up to 35-60% by cropping system diversification. Life cycle assessment models indicated that fossil energy use, emissions of greenhouse gases, and emissions of various air pollutants were all reduced significantly as rotation length increased, but were unaffected by herbicide regime. Taken together, results of this long-term study indicate that diversification of conventional corn-soybean systems can allow for large reductions in the use of herbicides and lead to less environmental and human health damage, higher crop productivity, and equivalent profitability.

Principal Investigator(s)

Matt Liebman

Year of Grant Completion