Phosphorus Extraction by Cotton Fertilized with Broiler Litter

Received for publication August 22, 2006. Knowledge of the magnitude of P extracted and removed by harvested crop is an important component of effectively managing poultry litter to minimize or prevent the buildup of P in soil. This knowledge does not exist or is not well documented in cotton fertilized with litter as the primary fertilizer. The objective of this research was to quantify the magnitude of P extracted by cotton when fertilized with broiler litter and to determine whether supplementing litter with inorganic N improves P extraction. The research was conducted from 2002 to 2004 on two commercial farms representing a conventional-till at Cruger and a no-till at Coffeeville, MS, USA. At each location, the treatments consisted of an unfertilized control; a farm standard (STD) fertilized with inorganic fertilizers; and broiler litter of 2.2, 4.5, and 6.7 Mg ha^–1 in an incomplete factorial combination with 0, 34, or 67 kg ha^–1 N as urea ammonium nitrate (UAN) solution. The unfertilized control extracted an average across years of 27.7 kg P ha^–1 at Cruger and 26.0 kg P ha^–1 at Coffeeville. Application of both litter and UAN-N decreased tissue P concentration but increased extracted amount of P because of increases in dry weight. The largest end-of-season P extraction in this research, which included 53.9 kg P ha^–1 in 2004 at Cruger and 49.3 kg P ha^–1 in 2002 at Coffeeville, was recorded for the treatment that received the largest litter rate of 6.7 Mg ha^–1 supplemented with 34 or 67 kg ha^–1 UAN-N. Applied P always exceeded extracted P in all 3 yr at both locations when the litter rate was 4.5 or 6.7 Mg ha^–1. Extracted P equaled or exceeded applied P when 2.2 Mg ha^–1 litter was applied. Increasing litter rate decreased phosphorus extraction efficiency (PEE) while supplemental UAN-N increased PEE. An average of 53% of the total P extracted was partitioned to seed with an additional 2.4% partitioned to lint for a total of 55% that would be removed with harvested crop. Nitrogen fertilization appeared to shift P partitioning from vegetative to reproductive parts. Supplementing litter with inorganic N may be an effective strategy not only in extracting additional P from soils but also in increasing the fraction partitioned to seed so that more P is removed from the field.