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

Traditional teaching on P behavior in soil emphasized its retention, and therefore conservation programs to reduce P loss from agricultural soils focused on reducing soil erosion. More recent observations in the Great Lakes watershed suggest that losses of dissolved forms of P are increasing. Combined trends in tillage practices, along with timing and placement of fertilizer and manure, may drive this increase in loss of dissolved P. This project aims to assess the effect of timing and placement on losses of dissolved and particulate forms of P. The project will have three major objectives: i) controlled runoff studies assessing fertilizer and manure P placement/incorporation; ii) controlled runoff studies assessing commercial fertilizer placement and timing to first runoff event; and iii) 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, will be placed in controlled environment runoff boxes 40 inches long, 8 inches wide and 4 inches deep. Treatments will compare surface broadcast, incorporation, surface band, and subsurface band application methods. Sources of P will be monoammonium phosphate fertilizer, solid cattle manure and liquid swine manure, each applied at a rate to supply 90 lb of P₂O₅/A. Artificial rainfall, representing a storm of 1 in 5 years frequency, will be applied 7 days after P application, and again 7 days after the first runoff event. Runoff water samples will be analyzed for total P, total dissolved P and dissolved reactive P. These measurements are set to take place in February to March 2016. A field site has been selected for the third objective.

One undergraduate and one graduate student are involved in this project. This project will contribute valuable information helping to quantify the water quality benefit associated with timing and placement of P.