Cover Crop and Fertilizer Management to Improve Water Quality.

Phosphorus fertilizer loss from agriculture production causes eutrophication of freshwater lakes and streams making them hazardous to human health and upsetting aquatic ecosystems by creating hypoxic zones. The Kansas Agriculture Watershed study was developed to understand the effect cover crops and fertilizer management practices have on reducing phosphorus loss via surface runoff. The study consists of 18 watersheds approximately 0.5 ha in size. Each watershed is equipped with a 0.46 m H-flume and automated water sampling equipment. Treatments are arranged in a factorial design with two levels of cover crop (with and without cover crop) and three levels of phosphorus fertilizer management (none, fall broadcast, and spring injected) replicated three times. The study is in a corn-soybean rotation under conventional tillage. The cover crop treatment is a mix of wheat, rapeseed, and hairy vetch. The cover crop was planted after the soybean harvest in the fall of 2014 and terminated before corn planting in the spring of 2015. Water samples were analyzed by the Kansas State University testing lab for total suspended solids, total phosphorus, and dissolved phosphorus. A wet spring in 2015 resulted in 12 rain events that caused runoff. Watersheds with the cover crop treatment had 17% less runoff than those without, reducing the total amount of sediment lost by 58%. Despite a late planting and less than ideal growth, the effect of the cover crop was still significant in throughout May, longer than expected. The management of the phosphorus fertilizer and the cover crop made a significant difference in the amount of dissolved phosphorus leaving each watershed. On treatments not receiving a cover crop, dissolved phosphorus loss was 5 times greater when broadcasted in the fall.  However, cover crops used in conjunction with fall broadcast fertilizer application reduced dissolved phosphorus loss by 45%. More research is needed to determine if broadcasting phosphorus fertilizer in the fall with a cover crop is comparable to a current best management practice of subsurface applying in the spring.