Conventional cropping systems in the U.S. Corn Belt are dominated by just two crops (corn and soybean), rely heavily on synthetic fertilizers and herbicides, and often emit pollutants to the environment. Ecological theory suggests that diversified cropping systems integrated with livestock should foster reduced reliance on agrichemical and fossil fuel inputs and should lower production costs and pollution. Since 2002, we have conducted a 9-hectare experiment in Boone, IA, to test the hypothesis that a four-crop system (corn/soybean/oat/alfalfa) receiving only small amounts of agrichemicals can match or exceed a conventionally managed two-crop system in weed suppression, yield, and profitability. Because weeds are a key factor affecting the performance of low-external-input (LEI) cropping systems, we focused particular attention on several components of weed population dynamics.
Results/Conclusions
Weed biomass was low in both the conventional and LEI systems, despite the use of 82% less herbicide in the LEI system. Over the period 2002-2006, soil seedbank densities of the weeds Abutilon theophrasti and Setaria faberi declined in both the conventional and LEI systems, though reductions were greater in the conventional system. Substantial losses of weed seeds to predators were detected during both warm (April-November) and cold (November-April) times of year. Trap data indicated that mice, field crickets, and carabid beetles were the most important granivores present. Phenological patterns of seed predation differed among crops in a manner that suggested ensembles of dissimilar crops should enhance the impacts of weed seed predators. Modeling analyses showed that seed predation could contribute strongly to regulation of weed density in the LEI system, but was unnecessary in the conventional system. Soil particulate organic matter carbon and nitrogen levels were greater in the LEI system than the conventional system, whereas petrochemical energy use and nitrate leaching were lower in the LEI system. Corn and soybean yields were as high or higher in the LEI system than the conventional system. Labor requirements were greater in the LEI system than the conventional system (3.41 vs. 1.82 hr ha-1 yr-1), but average returns to land and management during 2003-2006 were also greater in the LEI system ($540 vs. $504 ha-1 yr-1). With subsidies, differences between the systems in net returns were smaller, but rank order of the systems was maintained. Data from this experiment demonstrate that cropping systems can be redesigned for productivity, profitability, and improved environmental quality, and that ecological processes such as seed predation can reduce requirements for agrichemicals.
