Abstract 86

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

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

Australian-Journal-of-Agricultural-Research. 1989, 40: 6, 1217-1225; 14 ref.

In a field experiment in 1987-79, 0 or 50 kg P/ha as triple superphosphate was applied to Stylosanthes scabra cv. Seca, S. guianensis cv. Schofield or S. viscosa cv. CPI 34904. Leaf, stem, inflorescence, seed and litter K, Ca, Na and Mg concn were monitored over both wet and dry seasons. P application had no effect on the K concn of leaves, stems and litter but increased seed K concn. Application of triple superphosphate decreased Ca concn in all fractions despite its Ca content. P application increased Mg concn in all fractions but had no effect on Na concn. P application also increased the Ca:P ratio but had no effect on the changes in cation concn with time. As plant age increased, leaf K concn decreased in all 3 species, leaf Ca concn decreased in Seca and Schofield and leaf Na concn decreased in Seca and CPI 34904. Leaf Mg concn remained approx. constant. A comparison of cation concn in intact leaves and leaf litter suggested that there was remobilization of K, and to a lesser degree, Na and Mg but not Ca from old leaves prior to senescence. Leaf and green stem K and Ca contents were generally considered adequate for cattle requirements throughout the year. However, Mg and Na often fell below levels required for cattle growth. The wide Ca:P ratio combined with the low P concn in all 3 species suggested that cattle grazing these pastures would respond to P supplementation.