Ann M. Johanns

Increasing Cropping System Diversity Balances Productivity, Profitability and Environmental Health

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 fossil energy and agrichemicals, and large negative impacts on the environment. We hypothesized that cropping system diversification would promote ecosystem services that would supplement, and eventually displace, synthetic external inputs used to maintain crop productivity. To test this, we conducted a field study from 2003–2011 in Iowa that included three contrasting systems varying in length of crop sequence and inputs. We compared a conventionally managed 2-yr rotation (maize-soybean) that received fertilizers and herbicides at rates comparable to those used on nearby farms with two more diverse cropping systems: a 3-yr rotation (maize-soybean-small grain + red clover) and a 4-yr rotation (maize-soybean-small grain + alfalfa-alfalfa) managed with lower synthetic N fertilizer and herbicide inputs and periodic applications of cattle manure. Grain yields, mass of harvested products, and profit in the more diverse systems were similar to, or greater than, those in the conventional system, despite reductions of agrichemical inputs. Weeds were suppressed effectively in all systems, but freshwater toxicity of the more diverse systems was two orders of magnitude lower than in the conventional system. Results of our study indicate that more diverse cropping systems can use small amounts of synthetic agrichemical inputs as powerful tools with which to tune, rather than drive, agroecosystem performance, while meeting or exceeding the performance of less diverse systems.

The Long-Term Agroecological Research (LTAR) Experiment Supports Organic Yields, Soil Quality, and Economic Performance in Iowa

The Long-Term Agroecological Research (LTAR) experiment, at the Iowa State University (ISU) Neely-Kinyon Farm in Greenfield, IA, was established in 1998 to compare the agronomic, ecological, and economic performance of certified organic cropping systems to conventional counterparts. Cropping systems were designed based on local farmer input and practices. In the second LTAR phase (2002 to 2010), equivalent organic and conventional corn (Zea mays) and soybean (Glycine max) yields were achieved in the organic corn-soybean-oat (Avena sativa)/alfalfa (Medicago sativa) (C-S-O/A) and corn-soybean-oat/alfalfa-alfalfa (C-S-O/A-A) rotations compared to the conventional corn-soybean rotation (C-S). Organic oat and alfalfa yields, at 103 bu/acre and 4.4 tons/acre, respectively, exceeded county averages of 73 bu/acre and 3.3. tons/acre, for the same period. Similar plant protection occurred in organic crops, without the use of petrochemicals, compared to conventional crops maintained with synthetic pesticides. In Fall 2009, soil organic carbon, total nitrogen, and extractable K and Ca were 5.7%, 9.5%, 14.2%, and 10.8% higher in organic soils, respectively. Soil properties related to biologically active organic matter were up to 40% higher in organic soils. Economic returns to land and management in 2010 were

Iowa corn and soybean county yields

510/acre in the organic C-S-O/A-A rotation compared to

Energy and Economic Returns by Crop Rotation

351/acre in the C-S rotation. The LTAR experiment will be continued as a valuable demonstration of the potential for organic crops to achieve comparable yields while increasing carbon sequestration and economic returns compared to conventional corn and soybean rotations.