Effects of phosphorus and superphosphate on the growth of Urochloa species

Abstract

Six Urochloa accessions (U. mosambicensis cv. Nixon, CPI 46876, CPI 47167; U. oligotricha CPI 45607, CPI 47122, CPI 47 124) were grown in pots of phosphorus-deficient soil with varying rates of added phosphorus and their phosphorus requirements and responses compared. The same six accessions were grown in swards at Lansdown near Townsville with Stylosanthes hamata cv. Verano and S. scabra cv. Seca and their responses to superphosphate measured over a five-year period. All accessions gave large responses, both to phosphorus in pots and superphosphate in the field, with only small differences between accessions in their phosphorus requirements. Phosphorus application increased phosphorus concentration in the tops, from 0.11 to 0.17% without phosphorus, to 0.56-0.70% at 200 kg P/ha, but had little effect on nitrogen concentration. In the final year of the field trial, superphosphate did not significantly affect yield of the sown legume but yields of Urochloa were significantly increased by superphosphate application. This resulted in the nil superphosphate plots being legume dominant (mainly S. hamata) and the high superphosphate plots being Urochloa dominant.