Monday, November 13, 2006

Soil Management Induced Changes in Active Phosphorus Pools and Activities of Phosphatases in Mixed Prairie Ecosystems.

Eirini Katsalirou, Shiping Deng, and David L. Nofziger. Oklahoma State Univ, Dept of Plant and Soil Sciences, Stillwater, OK 74078-6028

Understanding phosphorus (P) cycling and dynamics of soil P pools are important in developing management practices to maintain ecosystem health.  The objective was to determine impacts of management practices on different P-pools and enzyme activities involved in P transformations.  Surface soil samples were taken from rolling upland mixed prairie in south central US.  Treatments included (1) undisturbed, (2) abandoned (was cultivated but returned to grassland >30 yr ago), (3) moderately grazed, (4) heavily grazed, and (5) cultivated with continuous winter wheat.  Microbial biomass P (Pmic), organic P (Porg), inorganic P (Olsen-P), total P (Pt), and activities of alkaline and acid phosphomonoesterases, phosphodiesterase, and inorganic pyrophosphatase were determined.  Of the soil ecosystems evaluated, the cultivated one had the lowest Pmic and phosphatase activities, but the highest Porg and Olsen-P.  The lack of external inputs of inorganic P in the grazed and undisturbed soil ecosystems demanded microorganisms to decompose complex organic P compounds, leading to reduction of Porg pool.  Moreover, the partial removal of plant biomass by grazing stimulated new plant growth, increased accumulation of belowground organic compounds, and enhanced microbial biomass and soil enzyme activities.   In general, cultivation diminished microbiological and biochemical activities, and Pmic pools, while grazing and undisturbed grassland maintained and/or enhanced these activities and P pools.  The significantly higher Pmic, Porg, and phosphatase activities in the abandoned soils than the cultivated ones suggested partial restoration of the soil ecosystem from impact by cultivation.  Based on evaluation of different soil P pools and phosphtase activities, the grazed systems were not distinguishably different from the undisturbed, suggesting that grazing did not have detectable impact to ecosystem health and function.  Thus, grazing is a sustainable management system.