Examination of phosphorus in agricultural soils of New York's Delaware River watershed

Diffuse phosphorus loss from agricultural land represents a major source of pollution to water bodies in the United States. Soil P saturation relates the capacity of a soil to bind soluble P to the quantity of P already held by the soil, and is a key environmental indicator of non-point source pollution potential.; Chapter Two evaluates a new method of interpreting P quantity-intensity relationships to measure soil P saturation (Psatqi), comparing Psatqi to soil P saturation estimated by oxalate extraction (Psat ox). Psatqi and Psatox were measured in soils from across the Delaware River Watershed. The two indicators were significantly related by first order model (R2 = 69%). Threshold soil P saturation levels were estimated by analyzing the distribution of Psatqi across all soils: Psatqi = 116 mug P*g--1; Psat ox = 32%. Because P quantity-intensity relationships describe P sorption behavior for all soils, Psatqi provides a more universal estimate of soil P saturation than Psatox.; A practical limit to the use of soil P saturation to identify pollution potential is the paucity of environmental analyses offered by soil testing laboratories. Chapter Three examines associations between readily available soil test data and soil P saturation. Soil test data provided strong prediction of soil P saturation. Results indicate that pedotransfer functions could be developed by soil testing laboratories to estimate soil P saturation from agronomic soil test data.; Chapter Four presents the results of an observational study in which P fractionation was conducted on soil samples collected from contiguous alfalfa, corn and forest soils on three occasions from June, 1997 to May, 1998. Application of starter fertilizer in 1997 resulted in temporary increases in Ca-P i and soluble-Pi in the upper 5 cm of the corn field soil, increasing P source risk. Manure addition to cultivated soils did not increase soluble-Pi significantly, reflecting equilibrium of quantity/intensity factors. Incorporation of manure minimized source risk during the growing season. Organic P was highest in the forest soil where SOM was elevated above that of cultivated soils and P additions derived from detritus. Temporal variations if Fe/Al-Pi revealed the influence of pH on this pool.