Minimizing Phosphorus Loss with 4R Stewardship and Cover Crops

The objectives of this research are to determine how interactions between cover crops and P fertilizer management impact P loss, P use efficiency, crop yield, and net return. A watershed study at the Kansas Agricultural Watershed Field Laboratory near Manhattan, KS has been established to address these objectives. The study consists of 18 small (1.2 to 1.5 A) watersheds equipped with automated runoff monitoring equipment. Treatments include: 1) no P fertilizer, no cover crop, 2) no P fertilizer, with cover crop, 3) fall-broadcast P, no cover crop, 4) fall-broadcast P, with cover crop, 5) spring-injected P, no cover crop, and 6) spring-injected P, with cover crop. The site has a history of a conventional tilled wheat-soybean rotation, but for this study a no-till corn-soybean rotation will be adopted.

The first planting for this experiment was in the spring of 2015. Due to prior management, this first year of data is for conventional tillage, and succeeding years will all be no-till. Annual precipitation for 2015 was near normal. Average corn yield was 160 bu/A with no yield difference between treatments. There were 12 rainfall events that produced runoff during the year (October to October). The first runoff occurred on May 4 and last on September 10.

Erosion was highest (6.2 t/ha) with conventionally tilled corn on the no cover crop plots, where over 90% of the P loss was attached to sediment. Use of a cover crop reduced runoff by 16% (25 mm) and reduced erosion by over 50%. With the reduced erosion, the cover crop also reduced total P loss by over 50%. Fertilizer treatments (control, fall broadcast, spring injected) did not affect runoff, sediment loss, or total P loss. However, dissolved P loss was significantly affected by both cover crop and fertilizer placement. Fall-broadcast fertilizer treatments (without cover crop) had nearly 10 times more dissolved P loss than the control or spring-injected treatments. Cover crop did not affect dissolved P loss on the control or spring-injected treatments, but cover crop reduced dissolved P loss by 60% for the fall-broadcast treatment. Initial results indicate that cover crops can be an excellent best management practice to reduce dissolved P loss from fall-broadcast fertilizers in conventionally tilled corn. Future efforts will investigate cover crop and fertilizer management effects in no-till corn-soybean production. This project will continue in 2016.