Minimizing Phosphorus Loss with 4R Stewardship and Cover Crops


02 Jun 2018

2017 Annual Interpretive Summary

The objectives of this research are to determine how interactions between cover crops and phosphorus (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) has been established to address these objectives. The study consists of 18 small (1.2 to 1.5 acre) watersheds equipped with automated runoff monitoring equipment. Treatments for the study (replicated 3 times) include: 1) no P fertilizer and no cover crop; 2) no P fertilizer, with cover crop; 3) fall-broadcast P and no cover crop; 4) fall broadcast P, with cover crop; 5) spring injected P and 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 was adopted in 2015.

Results from the third year of the study, which was the second year of no-till, were consistent with results from the prior two (2015 and 2016) years. Cover crops decreased sediment loss by 70% and also decreased particulate P loss by 40%. Although cover crops were effective at reducing sediment and particulate P loss, dissolved P loss increased. Sub-surface application of P fertilizer decreased total P loss by about 30% and dissolved P loss by about 40%. Relative to a fall broadcast application, sub-surface P application tended to maintain lower total P and dissolved P losses during the March and April runoff events which were prior to corn planting. Averaged across all cover crop treatments, fall broadcast and spring injected P fertilizer increased corn yield by 18%, from 95 to 112 bu/ac. The use of a cover crop decreased corn yield by 26%, from 122 bu/ac without cover crop to 90 bu/ac with cover crop.

Copies of presentations are available on the project web site at This study will continue in 2018 with no-till soybean as the primary grain crop. The fifth and final year of the study will begin following soybean harvest when cover crops will be direct seeded into soybean residue.