PHOSPHORUS MOBILITY IN CALCAREOUS SOILS UNDER HEAVY MANURING

Confined animal production systems produce large amounts of manure tha t are usually disposed on limited land areas in proximity to the sourc e. There is concern that continuous heavy manuring may saturate the so il's capacity to retain manure-P and result in groundwater contaminati on with excessive P. The objectives of this research were to determine the fate of waste-P in heavily manured soils and assess the risk of s oil and water quality degradation in turkey (Meleagris gallopavo) and beef (Bos taurus) feed lot production areas. All soils were calcareous throughout the profile. Samples were collected by 30-cm depth increme nts to a depth of 210 cm or a limiting layer and were analyzed for NaH CO3-extractable P (including inorganic and organic), and total soil P. Large amounts of extractable organic P in the surface soil layers dec reased to background levels within 2 to 3 yr after manuring ceased. In heavily manured fields extractable inorganic P was well above backgro und concentrations to as deep as 210 cml apparently because of mo-ceme nt and subsequent mineralization of organic P, Organic matter in these soils was about twofold higher than background levels. There appeared to be no practical limit to the P-retention ability of these calcareo us soils. Under these conditions the risk of groundwater contamination bg organic or inorganic P from waste P disposal to land is negligible .