The Long-Term Agroecological Research (LTAR) Experiment in Iowa: Organic Resilience in Soil Quality and Profitability.

The Long-Term Agroecological Research (LTAR) experiment, at the Iowa State University Neely-Kinyon Farm in Greenfield, Iowa, was established in 1998 to compare the agronomic, ecological and economic performance of conventional and organic cropping systems. The certified organic systems are designed to substitute local, renewable input sources in contrast to inputs based on off-farm energy, and to increase the internal resilience of agroecosystems, which consequently increases their adaptability to potential climate changes. Cropping systems compared the following crop rotations, using identical crop varieties, with each crop in each rotation repeated four times every year: C–S: conventional corn (Zea mays L.)-soybean [Glycine max (L.) Merr.]; C–S–O/A: organic corn-soybean-oat (Avena sativa L.)/alfalfa (Medicago sativa L.); and C–S–O/A–A: organic corn-soybean-oats/alfalfa-alfalfa. Organic cropping systems were shown to provide similar or greater yields, higher soil quality, and much higher economic returns than a conventional corn-soybean rotation, based on thirteen years of data from a side-by-side comparison experiment at the LTAR. 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. Corn yields in the organic C-S-O/A-A rotation averaged 99% of the average conventional corn yield, compared to 92% in the C-S-O/A rotation. Organic soybean yields were 5% and 4% greater in the C-S-O/A and the C-S-O/A-A rotation, respectively, than conventional soybean yields. 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. Similar plant protection occurred in organic crops compared to conventional crops.  Economic returns to land and management in 2010 were $510/acre in the organic C-S-O/A-A rotation compared to $351/acre in the C-S rotation, and throughout 13 years of the LTAR study, organic systems returned roughly $200 per acre more than conventional crops. Organic crops fetch a premium price in the market based on high consumer demand, and, with the elimination of the need for expensive inputs like herbicides and synthetic fertilizers, economic returns will continue to rise. These results have encouraged the transition to more ecologically-diverse methods of farming in Iowa.