Phosphorus requirements and responses of tropical pasture species: native and introduced grasses, and introduced legumes

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Abstract
Plants of five native or naturalized grasses (Bothriochloa pertusa, Chloris barbata, Chrysopogon fallax, Digitaria ciliaris, Heteropogon contortus), eight introduced grasses (Andropogon gayanus CPI 57497, Cenchrus ciliaris cv. Biloela, Chloris gayana cv. Callide, Chrysopogon sp. CPI 52213, Dichanthium annulatum CPI 50819, Paspalum plicatulum cv. Rodd's Bay, Urochloa oligotricha CPI 47122, U. mosambicensis CPI 46876) and three introduced legumes (Macroptilium atropurpureum cv. Siratro, Stylosanthes hamata cv. Verano, S. scabra cv. Seca) were grown in pots of phosphorus deficient soil with varying rates of added phosphorus. Their phosphorus requirements and responses were compared. The two Stylosanthes species were the least responsive of all. Among the grasses, C. fallax, A. gayanus and B. pertusa were the least responsive and D. ciliaris, C. gayana and D. annulatum the most responsive. The increases in yield when phosphorus was applied were mainly due to increases in tiller numbers, with smaller increases in rate of leaf appearance and leaf size. Digitaria ciliaris, U. oligotricha and C. barbata required smaller additions of phosphorus to achieve near maximum yields than did other species. Bothriochloa pertusa and D. annulatum required the most. Critical phosphorus concentrations in whole tops at 35 d (immediate pre-flowering stage) ranged from 0.20% in C. ciliaris to 0.39% in S. hamata. Overall, critical phosphorus concentrations in whole tops were similar to those in the youngest expanded leaves. When the species were grouped on the basis of their phosphorus requirements in the field, the groups were more closely related to responsiveness to applied phosphorus than to the amount of applied phosphorus required for near maximum yield. Species tolerant of low phosphorus conditions (e.g. Stylosanthes) gave smaller responses than less tolerant species (e.g. D. ciliaris and U. mosambicensis).