Rotation Strategies for Balancing Multiple Management Objectives in Organic Cropping Systems.

Balancing weed suppression, beneficial insect conservation, environmental quality and profitability is challenging in organic cropping systems due to reliance on soil disturbance for weed control. We hypothesized that adverse tillage impacts can be mitigated by "rotating" soil depleting with soil building activities. We conducted a 4-year experiment to compare four organic feed and forage cropping systems. The experiment, repeated twice, was initiated in 2007 (Start 1) and 2008 (Start 2). System 1 included an intermediate level of disturbance with annual cover crops, followed by two years of alfalfa. System 2 included an intermediate level of disturbance with annual forage followed by two years of alfalfa/orchardgrass. System 3 included a high level of disturbance with a bare fallow, small grain, and a triticale/vetch cover crop followed by no-till corn. System 4 included minimal disturbance with perennial grass and legume cover crops, followed by tilled corn. To assess cumulative system effects, we established a soybean uniformity trial across all systems in Year 4. We compared system profitability using net present value analyses. The uniformity trial and cumulative results indicate that the perennial-based Systems 1 and 2 outperformed Systems 3 and 4 in weed control, while maintaining soil quality and profitability. Average soybean yields in the uniformity trial were more than 30% greater in Systems 1 and 2, than in Systems 3 and 4. The soybean yield differences reflect differences in weed abundance, which was four times higher in Systems 3 and 4 following corn than in Systems 1 and 2 following alfalfa. Particulate organic matter nitrogen was maintained or increased over the first three rotation years in all systems. In Start 1, all systems had a positive net present value. In Start 2, only Systems 1 and 2 were profitable. Our results indicate that the integration of perennial forage crops into annual, grain-based rotations can achieve multiple management objectives.