It is assumed that land-use change has less effect on soil phosphorus (P) than on soil carbon (C) and nitrogen (N). Little is known, however, about the changes in soil P pools during prolonged arable cropping in semiarid grasslands. In this research, we measured changes in phosphorus pools of soil that had been cropped for 0-98 years in the South African Highveld. Hedley sequential extraction was carried out on bulk soil samples and size fractions to quantify inorganic and organic P pools along this temporal gradient. Total P content did not change with prolonged arable cropping, indicating that P removed by crops was compensated for by fertilizer application. The contributions of inorganic P (P-i) to the total P of bulk soil increased from 37 to 63%, with a corresponding decrease in organic P (P-o). After approximately 60 years of cultivation, a steady-state equilibrium was approached in all P fractions, which was characterized overall by smaller P-o and larger Pi contents. These temporal dynamics were controlled mainly by P pools in the sand fraction and by the 0.1 m NaOH pool from the Hedley fractionation. Increases in P-i may reflect inorganic fertilizer applications, whereas losses in P-o were attributed to crop harvest, erosion and mineralization of organic matter. Arable cropping affected both labile and stable P pools after land conversion, indicating that stable P pools were not mere sinks, but also slowly available sources of plant-available P.