Effects of superphosphate application and cutting interval on native pastures in the Clarence Valley, New South Wales

Abstract

The effects of superphosphate rate (nil; 250 kg ha-l initial with 125 kg ha-1 maintenance; and 500 kg ha-1 initial with 250 kg ha-1 maintenance) and cutting interval (2, 4, 6 or 8 weeks) on dry matter yield, growth rate, botanical composition and chemical composition of native pastures on a sandstone soil in the Clarence Valley, New South Wales were studied over a period of three years. Mean annual dry matter yield of unfertilized native pasture was 990 kg ha-l and this was increased to 1322 kg ha-1 at the higher rate of superphosphate. Dry matter yield was depressed from 1587 to 647 kg ha-1 by decreasing cutting interval from 8 weeks to 2 weeks. Pasture growth was limited to the September to May period and 87 per cent of the total annual production occurred in summer and autumn. Maximum growth occurred in the February/March period, with 16.2 kg ha-1 day-1 being the maximum recorded for the unfertilized pasture and 19.9 kg ha-1 day-1 for pasture at the higher rate of superphosphate. Changes in botanical composition were neither large nor consistent. Phosphorus content of the native pasture averaged 0.12 per cent. Crude protein content averaged 7.4 per cent, with levels in standing herbage in winter-spring falling to 3 per cent. Phosphorus yield was 1.1 kg ha-1 year-1 and crude protein yield was 65.8 kg ha-1 year-1. Superphosphate increased phosphorus content and yield, and crude protein yield. Increasing cutting interval decreased phosphorus and crude protein contents but increased phosphorus and crude protein yields by its effect on dry matter yield. Maximum yields obtained were 3.3 kg ha-1 year-1 phosphorus and 100 kg ha-1 year-1 crude protein. It was concluded that the increases obtained would be insufficient to produce worthwhile improvements in animal production, and that an increase in the legume content of these pastures is required before this could occur.