Long-term cattle manure application in soil - I. Effect on soil phosphorus levels, microbial biomass C, and dehydrogenase and phosphatase activities

Studies were conducted to investigate the effects of long-term management practices on level and distribution of soil P and enzyme activities involved in P transformations in soil. Treatments included manure, P, NP, NPK, and NPK plus lime. Cattle manure was applied every 4 years at 269 kg N ha(-1) for over a century and chemical fertilizers were applied every year at 67 kg N, 14.6 kg P, and 28 kg K ha(-1) for over 69 years. Total soil P increase in soils ranged from 4.5 to 10.3 kg P ha(-1) year(-1) with the highest increase detected in the P-treated and the lowest in the manure-treated plot. Approximately 77-86% of the applied inorganic fertilizer-P in the past 69-71 years was recovered either in the harvested grain or remained in the top 30 cm of soil, while only 32% of the applied manure-P was recovered. Microbial biomass C and activities of alkaline phosphomonoesterase, phosphodiesterase, inorganic pyrophosphatase, and dehydrogenase were significantly higher in the soil treated with cattle manure. Acid phosphomonoesterase activity, however, was significantly higher in soils treated with chemical fertilizers. Results from this study suggested that manure-P is relatively more mobile than inorganic fertilizer-P. Long-term application of cattle manure promoted microbiological activities and P cycling, but did not result in P accumulation to levels close to those in inorganic P fertilizer-treated soils.