The nutrition of ruminants grazing native and improved pastures. IV.* Long-term effects of the quantity of superphosphate applied on the nutritive value of the diet selected by sheep grazing a pasture originally sown to Phalaris aquatica and Trifolium repens

Abstract

Small plots sown to Phalaris aquatica–Trifolium repens in 1967 were fertilized with either 0, 188 or 375 kg superphosphate ha^-1 year^-1 from 1967 to 1976; the plots were grazed uniformly between 1967 and 1975 and at three stocking intensities during 1975 and 1976. The composition of the forage on offer and of the diet selected by grazing sheep were measured at 2-monthly intervals during 1976.

Phalaris largely died out from plots which did not receive superphosphate. Available forage, and its content of clover, nitrogen and most minerals were substantially greater on plots that received fertilizer, as were the digestibility and nitrogen content of the diet selected. The nutritive value of the diet selected was greatest on plots which received 375 kg superphosphate ha^-1 year^-1. The nitrogen content of the diet selected generally increased with increasing stocking intensity, but this trend was not evident for digestibility; interactions between the quantity of fertilizer applied and stocking intensity were not significant.

Digestibility and nitrogen content of the diet varied between months, with the quantity of green forage and clover on offer, and with the nitrogen content of the available forage.

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*Part III, Aust. J. Agric. Res., 29, 1301 (1978).