Phosphate immobilisation in an uncropped field experiment on a calcareous soil

From an uncropped field trial on a calcareous soil, residual phosphate was monitored as function of time. At the start of the experiment, superphosphate at a rate of 150 kg P per hectare was applied. Extractable phosphate, using 0.5 M NaHCO₃ as extractant, is declining in the control and fertilised plot at a different rate as function of ageing time, lasting more than 7 years. Intersection of the linear regressions expressing the influence of ageing time on the extractable phosphate occurs at 11.37±6.48 years. Total P in the arable layer remains constant throughout the whole duration of the experiment. H Marschner Section editor