Availability of phosphorus in organic manures compared with monoammonium phosphate

Abstract

Phosphorus (P) as monoammonium phosphate, cattle, pig and sheep faeces was applied at rates equivalent to 0, 200, 400 and 600 mg P to cores of undisturbed soil (469 ± 31 g air-dry weight) from an established, organically manured, grassland sward. Yields of herbage were measured over eight harvests by continuously cropping in a growth chamber and the effect of the various treatments on yield, P concentration in herbage and residual labile soil P was measured. Yields from the different P sources varied little over the eight harvests, although the total yield from the inorganic source was significantly greater ( P < 0·05) than those from the organic treatments. Organic manures did not increase herbage phosphorus concentration to the same extent as monoammonium phosphate, and at the end of the experiment extractable soil P levels in the latter treatment were twice those of the organic P sources. Residual extractable soil P levels were of the order: monoammonium phosphate > pig faeces > cattle faeces > sheep faeces.