Submitted to: Soil Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/3/1997
Publication Date: N/A
Citation: Interpretive Summary: The input of phosphorus in runoff from farm land can cause unwanted weeds to grow in many rivers and lakes. These weeds can consume most of the oxygen dissolved in water, causing fish to suffocate and die. As a result, states are trying to develop guidelines for phosphorus management that meet crop production goals but minimize the potential for water quality problems, particularly in areas with intensive livestock operations, where large amounts of phosphorus in manure are produced. Due to a lack of information on the fate in soil of phosphorus from manure, these guidelines are based on data for inorganic fertilizer phosphorus applied to crops. Thus, we compared the availability in a wide range of soils of phosphorus from poultry litter and inorganic fertilizer. After being added to soil, phosphorus from poultry litter was less available for plant uptake than that from fertilizer phosphorus. Thus, guidelines for managing the phosphorus in manure should be based on the availability in soil of manure phosphorus rather than fertilizer phosphorus. Further research shows soil type, e.g., calcium carbonate, clay, organic matter, and iron content, influences the availability of phosphorus from manure and inorganic fertilizers and the results will clarify manure management guidelines.
Technical Abstract: The potential for P loss in runoff can increase following land application of manure. As little information is available on the relative availability of manure and fertilizer P in soil, manure management recommendations are being based on fertilizer response. Thus, the availability of P (as Fe- oxide strip P) from poultry litter leachate or KH2PO4 was investigated by incubation for 7 d with 193 soils with a wide range of properties associated with P sorption. Phosphorus availability (F), calculated as the slope of the linear relationship (r2>0.91) between strip P and P added (0 - 108 mg inorganic P kg-1), was consistently greater for soils treated with KH2PO4 (mean Fk of 0.50) than litter leachate (mean Fl of 0.29). The availability of both P sources was inversely related to the total CaCO3 content of calcareous soils and extractable Fe and Al content of the remaining noncalcareous soils. The differential availability of the two sources of P is attributed to the complexation of P with Ca and soluble organic compounds in leachate. Thus, manure management recommendations should be based on the availability of manure P rather than fertilizer P in soil. Current fertilizer recommendations may be modified by soil CaCO3, extractable Fe and clay/organic C content to account for the differential availability in soil of manure P and mineral fertilizer P.