Monday, November 13, 2006 - 2:30 PM

Soil Phosphorus, Grain Yield, and Phosphorus Removal During Twelve Years of Phosphorus Management for Corn-Soybean Rotations.

Jacob Prater and Antonio P. Mallarino. Iowa State Univ, Dept of Agronomy, Ames, IA 50011

Due to the increased importance of conservation tillage and erosion control for agronomic and environmental P management there is a need for a better understanding of its cycling in agricultural systems under no-till production.  A study established in 1994 at five locations across Iowa has been conducted to gain a better understanding of P dynamics in corn-soybean rotations.  The study used broadcast and planter-band placement methods and multiple P rates to determine long-term effects on soil P, grain yield, and P removal with harvest.  Phosphorus rates based on existing estimates of P removal maintained or slightly increased soil-test P, while those above and below increased and decreased it.  The P placement had a negligible effect on yield except for an occasional and small advantage of banding due to dry conditions in surface soil, but did have a significant effect on reducing stratification.  Results showed that P fertilization increased P removal through effects on both yield and grain P concentration.  However, grain P concentration was uncorrelated with grain yield and poorly correlated with soil-test P. Average grain P concentration estimates used in Iowa for soil P maintenance (3.0 and 6.5 g P kg-1 for corn and soybean) were among the highest concentrations observed.