Minimizing Phosphorus Loss with 4R Stewardship and Cover Crops

The overall objective of this research is to determine how interactions between cover crops and P fertilizer management impact P loss, P use efficiency, crop yield, and net return. A replicated small watershed study at the Kansas Agricultural Watershed Field Laboratory near Manhattan, Kansas has been established to achieve the objectives. The study consists of 18 small watersheds (1.2 to 1.5 A each) equipped with automated runoff monitoring equipment. The following treatments will be applied: 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 conventionally tilled wheat-soybean rotation, but for this study a no-till corn-soybean rotation will be adopted, with first planting in the spring of 2015. There are no results to report to date since most efforts gone into site preparation, and there have not yet been runoff events.

The summer of 2014 was spent reconstructing terraces, re‐grading channels, constructing waterways, and installing pipe outlets to segment the research site into the 18 small watersheds. During the summer and fall each watershed outlet was equipped with a 1.5 ft. H‐flume permanently mounted on a concrete pad equipped with an automated water sampler, bubble‐type pressure transducer, data logger, batteries, and solar panel for continuous measurement of runoff and automated collection of water samples. Fall soil sampling across the watersheds indicated that soil test P concentrations ranged from 15 to 19 ppm, all below the critical value of 20 ppm (Mehlich 3). Soil pH ranged from 5.9 to 6.2. Lime was applied and incorporated to adjust the soil pH to the 6.0 to 6.5 range.

After site construction and preparation was completed, a cover crop (hairy vetch, rapeseed and winter wheat) was planted in appropriate watersheds, after which broadcast P fertilizer was applied. Cover crop biomass and nutrient uptake will be measured at the time of termination. Corn will be planted following cover crop termination in April, at which time the remaining fertilizer treatments will be applied. This project is planned to run through the end of 2019.