Amounts and Forms of Dissolved Phosphorus Lost with Surface Runoff as Affected by Phosphorus Management and Soil Conservation Practices

October 25, 2017

Antonio Mallarino, Mazhar U. Haq

Issue: Surface runoff accounts for the majority of phosphorus (P) from Iowa fields delivered to streams. Important fractions of runoff P are dissolved reactive P (orthophosphate P) and particulate (sediment-bound) P. Dissolved P is readily available to aquatic organisms and a large proportion of particulate P becomes available over a period of time depending on properties of the receiving water body. Recent surveys of Iowa streams and in the Lake Erie watershed suggest the amount of dissolved P loss from fields and its impact on water quality is greater than often assumed. Iowa research has shown higher orthophosphate P loss with fertilizer than with manure, and some conservation practices that reduce erosion and particulate P loss may not affect or may even increase dissolved P loss. Objective: The goal of this project is to study dissolved P in runoff for a wide range of soil P levels, fertilizer and manure P management practices, and soil conservation practices. Specific objectives are to determine the amount of runoff dissolved P not measured by the commonly used dissolved reactive P method, and study how amounts of different dissolved P forms in runoff can be estimated by soil-test P methods recommended for crops, water-extractable soil P, and an index of soil P saturation. Approach: About 900 soil and runoff samples from other ongoing and recently completed experiments will be analyzed. These samples represent field experiments managed with natural or simulated rainfall that included different soil-test P levels, crops, fertilizer and manure P placement methods and times of application, tillage systems, soil or manure amendments, corn harvesting systems, and the conservation practices cover crops and buffer grass strips.

Grant provided by: The Iowa Nutrient Research Center