Effect of superphosphate, or its component elements (phosphorus, sulfur, and calcium), on the grazing preference of steers on a tropical grass-legume pasture grown on a low phosphorus soil

Abstract

A Stylosanthes-based mixed tropical grass-legume pasture, grown on a phosphorus (P) deficient (<5 ¦g/g of available P) yellow earth soil near Townsville, north-eastern Queensland was used to assess the effects of fertiliser application on grazing preference. Unfertilised plots and plots fertilised with Pssulfur (S)+calcium (Ca) (superphosphate), P+S+Ca+sodium (Na), P+Ca+Na, P+S+Na, P+Na, P+Ca, S+Ca, S+Na, and S+Ca+Na were grazed by steers, and the grazing pattern was observed. Steers preferred plots fertilised with P (P+) in both autumn (May) and summer (February); no preference was shown for plots fertilised with S, Ca, or Na, or mixtures of these, compared with unfertilised control plots. Although P+ plots had higher herbage yields than plots not fertilised with P (P0), removal of the effects of yield and of P concentration in the herbage by covariance analysis at the May grazing still resulted in large significant (P<0.01) differences in grazing preference between the P treatments. Furthermore, there was no correlation (r2 = -0.024 to +0.072) between yield and grazing preference within either the P+ or P0 treatments.