Wednesday, November 7, 2007 - 4:45 PM
319-5

Availability of Poultry Manure Phosphorus for Corn and Application Impacts on Soil Phosphorus.

Daniel E. Kaiser1, Antonio P. Mallarino1, David J. Wittry1, Brett L. Allen2, and John E. Sawyer1. (1) Agronomy, Iowa State University, Ames, IA 50011, (2) Northern Plains Agricultural Research Lab, USDA-ARS, 1500 N Central Ave, Sidney, MT 59270

The poultry industry is very important in Iowa and manure is being sold for its fertilizer value but there are doubts about manure P availability for crops. Eighteen field trials with corn included manure and fertilizer treatments arranged in a complete block, split-plot design. Main-plot treatments were a control and two manure rates. Subplot treatments were 0, 25, and 50 kg fertilizer P ha-1. Measurements were early plant growth and P uptake (V5-V6 stage), grain yield, grain P removal, and post-harvest soil-test P (STP). High N and K rates were applied across all plots. An incubation study with two soils, fertilizer, and manure from egg layers or turkeys evaluated P effects on STP under controlled conditions. Manure or fertilizer P increased early growth at 13 sites and P uptake at 15 sites, and responses were unrelated to STP or the P source. Grain yield was increased at 10 sites, where STP was < 21 mg kg-1 Mehlich-3 P. Fertilizer P in addition to manure did not increase early growth or grain yield. Bray-P1, Mehlich-3, and Olsen tests assessed manure and fertilizer P effects on soil P similarly, but fertilizer increased water-extractable P more than manure. The studies provided inconclusive evidence for differences in P availability between fertilizer and poultry manure P sources.