Minimizing Phosphorus Loss with 4R Stewardship and Cover Crops


22 May 2017

2016 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 A) watersheds equipped with automated runoff monitoring equipment. Treatments (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.

Similar to the first year of the study (2015), broadcast P applications resulted in higher dissolved P losses compared to sub-surface banding or no P application. Surface P applications also increased the total P loss in early spring, but later in the season the application method did not affect total P loss runoff. Cover crops decreased sediment loss by 70% and also decreased total P loss by 40% for a few runoff events in the spring, but had no other impact. Although cover crops decreased particulate P loss, dissolved P loss from cover crop treatments consistently doubled that of no cover crop treatments for the entire season.

The highest soybean yield was from the fall surface-broadcast P treatments (65 bu/A), second was the spring injected P treatment (63 bu/A), and the lowest grain yield was with the zero P control (58 bu/A). Cover crops did not have any impact on soybean yield.
Although the first year of data indicated that the cover crop could be a promising best management practice to decrease P loss from fall broadcast P, this was not supported by data from the second year of the study because of an increase in dissolved P loss from cover crop treatments. Factors responsible for this increase in dissolved P loss are under investigation.

The details and results from the first two years of this study have been recorded in an M.Sc. Thesis, available online at This study will continue in 2017 with no-till corn as the primary grain crop.