Availability of Phosphorus in Beef Cattle Manure for Corn and Soybean.

An efficient utilization of beef manure nutrients is important to improve the sustainability of animal and crop production systems and avoid unnecessary use of energy and non-renewable resources. Manure P management differs from inorganic P fertilizers in that there is large variation in P concentration, has organic and inorganic P forms, and its handling is more difficult. This study assessed at the field the crop-availability of solid beef cattle manure P from selected Iowa beef production systems. Four 2-year trials were established in soils testing low in P having contrasting properties. Treatments at each trial involved application of three P rates (0, 25, and 60 kg total P ha^-1) as di-ammonium phosphate fertilizer, bedded manure from a feedlot with a concrete floor, and manure from a feedlot with soil floor) in the fall before soils froze or in spring. The P was applied only once with incorporation into the soils disking before a corn crop at all sites, and soybean was grown the second year without new P addition. Corn and soybean grain yield was greatly increased by fertilizer and beef cattle manure P, but the increases did not differ between the P sources or the times of application at any site. The P sources did not differ either for corn early growth and P uptake when the high 60-kg P rate was applied, but the manures were less efficient than the fertilizer when the low 25-kg P rate was applied in spring (10% less on average across sites). Post-harvest soil-test P results showed no statistically significant differences between the P sources in any year. Overall, results showed that the crop-availability of beef cattle manure P is much higher than currently assumed (60 to 100% compared with fertilizer) in Iowa State University manure management guidelines.