Biogeochemistry of phosphorus associated with sustainable soil management

Implications for exhaustive plant removal of soil nutrients must be addressed for sound management decisions in sustainable agriculture. Excluding fertilizer P, soil P is derived entirely from the breakdown, or weathering, of P-bearing minerals in the soil. A finite quantity of soil P exists for replacement of P removed in crop harvests. This study quantifies the long-term field relationships between the sinks and sources of plant-available soil P. Additionally, the potential P-supplying capacity for soils from six geographical areas of the world is examined. Established P field studies at two sites in North Carolina were employed to quantify the effects of fertilizer P on the various fractions of soil P during an 18-year period. Inorganic soil P represented the primary sink and source of plant-available P at both sites. Organic soil P represented a sink and source of plant-available P in one sandy soil. These fractions of soil P represented sinks to plant-available P when fertilizer P was applied in excess of P removed in the grain harvest, and sources of plant-available P when fertilizer P was less than harvest removal. Inorganic soil P content and the relationships between the inorganic fractions were used to estimate sustainable crop production potential. The number of predicted crops agrees with the observed yield data. Fractionation of soil P in soils from various areas of the world provided comparisons of pedogenic development and sustainable crop production potential. Bio-accumulation of P towards the soil surface was implicated in soils in which organic soil P content increased relative to total P content, corresponding to pedologically older soils. Crop production potential was primarily dependent on P extracted with NaOH and HCl, except for one soil that had received large quantities of manure. Detailed characterization of the various soil P fractions provides a guide to sustainable management decisions relative to P requirements.