Abstract 85

Gilbert,-MA; Edwards,-DG; Shaw,-KA; Jones,-RK

Department of Primary Industries, Mareeba, Qld 4880, Australia.

Australian-Journal-of-Agricultural-Research. 1989, 40: 6, 1205-1216; 14 ref.

In a field experiment from May 1978 to Sep. 1979, Stylosanthes scabra cv. Seca, S. guianensis cv. Schofield and S. viscosa cv. CPI 34904 were grown on a soil of low acid-extractable P status (4 mg P/kg using 5 mM H2SO4) and given 0 or 50 kg P/ha. P application increased P concn in all 3 legumes, but did not affect its pattern of seasonal change throughout the year. The P (and N) concn in most plant parts decreased through the wet season to reach minima in the late dry season. However, in seed there was little seasonal variation. In the 2nd year, Seca was more efficient at taking up P and utilizing it for growth under low soil P conditions than Schofield. CPI 34904 was less efficient than Seca at taking up P, but also used P efficiently for growth. The efficient utilization of P in the leaves and stems of Seca and CPI 34904 meant that P levels were often below the level (0.12%) considered adequate for growth of grazing cattle. Dry season P concn in all 3 legumes were inadequate. When P was applied, P concn in leaf and green stem of all species were 0.12% during the wet season, but in the green stem of Seca and CPI 34904 then fell below this level during the dry season. Applied P slightly increased N concn in leaves, stems and whole plants of all species. N concn were adequate ( > 1.1% N) for maintenance of cattle liveweight at most times. Only in the late dry season did green stem of Seca contain insufficient N. P application had little effect on the distribution of P and N within the plants. All species held a large percentage (20-50%) of these nutrients in green stems, but CPI 34904 was exceptional in directing up to 60% of the P and N to inflorescence and seed at the expense of leaf and stem.