『Abstract
　Amounts of phosphorus (P) in inorganic and organic pools were determined for three noncalcareous and five calcareous surface soils (0-150 mm) which had been cultivated for at least 15 yr, and their virgin analogues, to ascertain if relative pool sizes or soil P fertility are being changed by cultivation and associated fertilizer application. The soils were representative of major agricultural areas of the USA, with total P concentrations ranging from 200 to 1920 mg kg^-1 (approximately 50％ inorganic P ) and P applications from 0 to 90 kg ha^-1 yr^-1. P forms in the pools and extractants used were as follows: inorganic P; loosely-bound (1.0M NH4Cl), nonoccluded (0.5M NH4F + 0.1M NaOH), occluded (citrate-dithionite-bicarbonate + 0.5M NH4F + 0.1M NaOH), and Ca bound (1.0M HCl) (calcareous soils only): organic P; labile (0.5M NaHCO3), moderately labile (1.0M H2SO4 + 0.5M NaOH), moderately resistant (0.5M NaOH/HCl soluble), and resistant (0.5M NaOH/HCl insoluble). Distribution of inorganic P in virgin noncalcareous soils was, on average, 2％ loosely-bound, 52％ nonoccluded, and 46％ occluded. Cultivation resulted in an increase in nonoccluded and decrease in occluded P. Average distribution in the virgin calcareous soils was 2％ loosely-bound, 11％ nonoccluded, 9％ occluded, and 78％ Ca-bound, with no significant change in pool size with cultivation observed. On average, organic P in the virgin soils was 7％ labile, 48％ moderately labile, 33％ moderately resistant, and 12％ resistant, with no significant change in relative amounts due to cultivation. Amounts of fertilizer P applied and organic P mineralized and immobilized in stable inorganic P pools during cultivation, were related to P sorption index of the soils. The conversion of organic to inorganic P may be reversed by management practices allowing a build up of soil organic matter. Since little change in amounts of loosely-bound inorganic and labile organic P was observed during cultivation, the more stable pools may represent a better estimate of long-term soil fertility.

Additional Index Words: labile P; P mineralization; P sorption』

(Introduction)
Materials and methods
Results and discussion
Conclusions
References