Water Quality in Organic Systems.

Non-point source contamination is a major water quality concern in the upper Midwestern USA, where plant nutrients, especially NO₃-N, are susceptible to leaching due to extensive subsurface draining of the highly productive, but poorly drained, soils found in this region. Environmental impacts associated with intensive mineral fertilization in conventional production have encouraged producers to investigate organic methods. Mechanisms underlying improved environmental conditions on organic farms have included an improved capacity for greater water and soil nutrient retention due to enhanced soil organic matter content from more diverse crop sequences and application of organic-based amendments, including cover crops and manure. The Organic Water Quality (OWQ) experiment, established in 2011, compares transitioning organic and conventional crop rotations and pasture systems. The experimental site is located at the Iowa State University Agricultural and Biosystems Engineering and Agronomy Research Farm, near Boone County, Iowa. The field site was cropped in a conventionally managed C-S rotation prior to planting an oat/alfalfa crop in 2006. The 4.1 ha site consists of 30 47.2 m x 47.2m field plots laid out in a randomized complete block design with five replications.  Installation of tile lines under each plot and instrumentation to collect water samples and monitor tile water flow and nutrient run-off, including flow barriers and sump pits, was completed in September 2011. The fully-instrumented, tile-drained plots isolate tile drainage from each plot and permit comparison of treatment effects on tile flow and tile nutrient concentrations. Three cropping systems were established in the spring of 2012. Each phase of the cropping system is present every year and identical, non-GMO varieties are planted in conventional and organic plots. Experimental treatments include an organically managed C-S-O/A-A rotation, an organically managed perennial pasture system (bromegrass, fescue, alfalfa, white clover) and a conventionally managed C-S rotation.