Phosphorus Extraction by Cotton Fertilized with Broiler Litter

Authors: Tewolde, Haile; Sistani, Karamat; Rowe, Dennis; Adeli, Ardeshir

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2006
Publication Date: 6/1/2007
Citation: Tewolde, H., Sistani, K.R., Rowe, D.E., Adeli, A. 2007 Phosphorus Extraction by Cotton Fertilized with Broiler Litter. Agron J. 99:999-1008

Interpretive Summary: Poultry litter, which is often viewed as a waste, is land-applied as a way of disposing it but also as a fertilizer. It contains disproportionately large amounts of phosphorus which is a major nutrient that has been known to cause surface water pollution. Land-applying litter as a fertilizer is a concern because phosphorus not extracted by the target crop is subject to runoff to surface waters and may harm the immediate environment. Using litter as a fertilizer would not be a concern if the target crop absorbs all or the majority of the phosphorus supplied by the litter. But it is not known or not well documented how much of the litter-phosphorus is removed from the soil by crops such as cotton. Knowledge of the amount of phosphorus extracted and removed by harvested crop would improve management of litter to minimize or prevent the buildup of soil phosphorus and reduce adverse impact on surface water. We used two commercial cotton farms representing no-till and conventional-till in Mississippi to study the magnitude of phosphorus extracted by cotton when fertilized with broiler litter and to determine whether supplementing litter with commercial nitrogen fertilizers improve phosphorus extraction. The research showed cotton fertilized with 3 ton litter per acre plus 30 or 60 lbs per acre inorganic nitrogen fertilizer extracted as much as 48 lbs per acre phosphorus which is about 7 lbs per acre more phosphorus than the largest phosphorus extraction reported in the literature. Phosphorus applied in litter always exceeded total extracted when applied litter rate was 2 or 3 ton per acre which suggests, at these rates, phosphorus accumulation in the soil over time is likely. Extracted phosphorus equaled or exceeded applied phosphorus when only 1 ton per litter was applied. Supplementing litter fertilization with commercial nitrogen fertilizer improved the efficiency of phosphorus extraction. An average of 55% of the total extracted phosphorus is recovered in seed and lint and therefore removed from the field in harvested crop. Commercial nitrogen fertilization appeared to increase the proportion of phosphorus recovered in seed and lint which suggests supplementing litter with inorganic nitrogen may be an effective strategy not only in extracting additional phosphorus from soils but also in increasing the fraction recovered in seed so that more phosphorus is removed from the field.

Technical Abstract: Effective management of litter to minimize or prevent the buildup of soil P requires knowledge of the amount of P extracted and removed by harvested crop. This knowledge does not exist or is not well documented for cotton fertilized with poultry litter. 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 on two commercial farms under conventional-till (CT) and no-till (NT) systems in Mississippi USA in 2002, 2003, and 2004. Under each system, total amount and efficiency of P extraction by cotton fertilized with fresh broiler litter rates of 2.2, 4.5, and 6.7 Mg ha-1 was determined in an incomplete-factorial combination with 0, 34, or 67 kg ha-1 N side-dressed as urea-ammonium nitrate solution (UAN). Extraction from an unfertilized control and a farm standard fertilization was also measured. Application of both litter and UAN-N significantly increased P extraction which was almost always due to increases in plant dry weight. Neither litter application nor UAN-N application increased P concentration in the different plant parts. To the contrary, increasing litter or UAN-N application had a decreasing effect on tissue P concentration. The largest end-of-season P extraction in this research, which included 53.9 kg P ha-1 in 2004 under the CT and 49.3 kg P ha-1 in 2002 under the NT, was recorded for the treatment that received the highest litter rate of 6.7 Mg ha-1 supplemented with 34 or 67 kg ha-1 UAN-N. The largest reported P extraction by mature cotton fertilized with inorganic fertilizers is 44 to 46 kg P ha-1. Applied P always exceeded extracted P in all three years under both tillages when the litter rate was 4.5 or 6.7 Mg ha-1 which suggests, at these rates, P accumulation in the soil over time is likely. Extracted P equaled or exceeded applied P when 2.2 Mg ha-1 litter was applied. P extraction efficiency (PEE), which is the efficiency by which cotton extracted litter-derived P after accounting for P supplied by the soil reserve, was as large as 46.6% under the CT and 40.9% under the NT among all treatments that received litter. Increasing litter rate decreased PEE while supplemental UAN-N improved PEE. An average of 52.7% of the total P extracted was partitioned to seed with an additional 2.4% partitioned to lint for a total of 55.1% 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.