Effects of nitrogen fertiliser and urine on pasture performance and the influence of soil phosphorus and potassium status

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Abstract
Pasture responses to 4 levels of urea fertiliser and a cow urine treatment were examined at 3 phosphorus (P) and 2 potassium (K) levels in soil. Urea increased reygrass growth and subsequently decreased clover growth. Nitrogen (N) fixation by clovers was reduced initially because of substitution by uptake of mineral N from the soil, and subsequently because of reduced clover yields. Plant recovery of fertiliser N was high, an estimated 93% at 25 kg/ha of N, whereas recovery of urine-N was only 30%. There was no interaction between Nand PorK affecting total herbage yield, clover yield, N fixation, chemical composition of herbage, or N recovery by herbage. There was an increase in total yield from urine at the high soil P level and a decrease in total yield at the high soil K level. The results suggest there is no requirement for extra P or K in the soil when low rates of N fertiliser are used.