Organic Rotations in the Wisconsin Integrated Cropping Systems Trial: Implications for Organic Agriculture in a Changing Climate.

The Wisconsin Integrated Cropping Systems Trial was established in 1989 by Dr. Joshua Posner (UW-Madison Agronomy), with the purpose of monitoring the long-term impacts of several different cropping approaches in the Upper Midwest. Central to the design of the trial was the question of how low-input organic systems compared to their conventional counterparts in terms of yield, profitability, and environmental impacts. The WICST experiment consists of six cropping system divided by enterprise type (three cash-crop, three dairy-forage).  The three cash-crop systems include a high-external input, continuous corn system (CS1); a moderate-external input, NT corn-soybean system (CS2), and an organic corn-soybean-winter wheat system with a clover/oat cover following straw harvest (CS3). The three dairy-forage systems include a high-input corn-alfalfa-alfalfa-alfalfa system (CS4); an organic corn-oat/alfalfa-alfalfa system (CS5), and a rotationally grazed pasture (CS6) system.  The organic treatment (although not certified due to research constraints) began in 1993. In 2002 the USDA's organic farming standards were adopted and the fields have been consistently managed in adherence to these guidelines for the past decade. From analysis of the data obtained over a decade of organic management, themes relating to the impact of weather extremes on organic production, as well as the impact of organic agriculture on climate change, have begun to emerge. Extreme weather events (i.e. exceptionally wet or exceptionally dry years) appear to have a variable impact on organic management. Due to challenges with weed management on wet soils, yields in organic plots in wet springs tended to be lower than those in conventional systems (organic vs. conventional corn: 72% in wet years, 96% in average years; organic vs. conventional soybean: 79% in wet years, 95% in average years). During the drought of 2012, organic corn performed comparably to continuous corn, but yields were lower than that of systems where tillage was minimized. Soil organic carbon changes and N₂O emissions per unit of N harvested were lower in the organic corn-soybean-wheat rotation than in continuous corn, despite the use of cultivation in organic production for weed management. Life cycle analyses (LCA) conducted on each of the six systems indicate that the organic corn-soybean- wheat rotation produced the lowest kg CO₂ eq ha^-1 yr^-1, in large part due to the exclusion of synthetic fertilizers from the system. The organic systems at WICST have performed quite well with respect to yield, profitability, and certain key environmental variables. Long term system sustainability however could be improved by reducing tillage and increasing inputs from cover crops and livestock manures.