Impact of Degree of Fertilizer and Manure Incorporation and Timing of First Runoff Event on Phosphorus Losses to Surface Runoff

Recent observations in the Great Lakes watershed suggest that losses of dissolved forms of phosphorus (P) from agricultural land are increasing. Combined trends in tillage practices, along with timing and placement of fertilizer and manure, may drive this increase in loss of soluble P. This project aims to assess the effect of timing and placement on losses of dissolved and particulate forms of P. The project has three major objectives: 1) controlled runoff studies assessing fertilizer and manure P placement/incorporation; 2) controlled runoff studies assessing commercial fertilizer placement and timing to first runoff event; and 3) a field study relating runoff and incorporation methods on P losses from fertilizer and manure.

For the first objective, three soils (of clay, silt loam, and sandy loam texture class) were placed in controlled environment runoff boxes (40-inches long, 8-inches wide and 4-inches deep). Treatments compared surface broadcast, incorporation, surface band, and subsurface band application methods. The three P sources were monoammonium phosphate fertilizer, solid cattle manure, and liquid dairy manure, each applied at a rate to match two years of crop removal from a typical corn-soybean rotation. Artificial rainfall, representing a storm of 1 in 10 years frequency, was applied 7 days after P application, and again 7 days after the first runoff event.

Losses of dissolved P were dramatically reduced in all three soils when fertilizer or manure was either subsurface banded or incorporated, as compared to being left on the soil surface. The results confirm that subsurface placement can reduce concentrations of dissolved P in runoff water several fold to levels that are close to targets set for the mitigation of harmful algal blooms in Lake Erie. Further analysis is continuing on a study assessing timing of application of monoammonium phosphate or ammonium polyphosphate in relation to wetting and drying events. In addition, a field study assessing the impact of fertilizer placement on runoff losses from fall to spring is still underway. Results are expected to inform the development of a risk assessment tool for P loss that is needed for implementation of 4R Nutrient Stewardship, one of the key strategies listed in the February 2018 Canada-Ontario Lake Erie Action Plan.