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Phosphorus fertilizer for nitrogen fertilized dairy pastures. 1. Long term effects on pasture, diet and soil

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Davison, T.M., Orr, W.N., Silver, B.A., Walker, R.G. and Duncalfe, F. (1997) Phosphorus fertilizer for nitrogen fertilized dairy pastures. 1. Long term effects on pasture, diet and soil. The Journal of Agricultural Science, 129 (2). pp. 205-217. ISSN 0021-8596

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Article Link: https://doi.org/10.1017/S0021859697004632


The phosphorus fertilizer requirements and long term productivity of nitrogen-fertilized Gatton panic (Panicum maximum cv. Gatton) pastures, grazed by lactating dairy cows, were evaluated over 7 years. Cows grazed at 2·6 cows/ha on pastures that received annually 100 or 300 kg N/ha at each of 0, 22·5 or 45 kg P/ha. Phosphorus treatments were applied as single superphosphate, balanced for calcium by applications of gypsum.

The soil had an initial available soil phosphorus content of 40 mg/kg (bicarbonate extraction). At zero P fertilizer (0P), extractable soil P declined at the rate of 1·9 mg/kg each year; at 22·5P it was maintained close to the original level while at 45P it increased at 6·6 mg/kg each year. Increased P fertilizer caused significant (P<0·01) increases in plant P concentration from year 2 onwards. In years 6 and 7 there was significantly less green pasture and leaf on offer in 300N pastures at 0P than with 22·5P and 45P. There was no influence of rate of P fertilizer at 100N on pasture quantity on offer in any year. There were clear trends at 100N of decreasing total pasture and green dry matter (DM) on offer over the 7 years, but not at 300N.

Cows at 300N consumed more leaf in the diet in autumn and winter than at 100N. Leaf was 55–60% of the diet in summer and autumn, but decreased to 21% (100N) and 37% (300N) in winter. Dead material in the diet was always higher at 100N. Pasture leaf percentage and leaf yield were the best individual predictors of leaf percentage in the diet. Diet P selected from pasture was reduced by the higher rate of N fertilizer in each season. Estimated P concentrations of the diet selected from pasture for summer, autumn and winter averaged 0·30, 0·38 and 0·28% DM for 100N and 0·19, 0·24 and 0·18% DM for 300N treatments, respectively.

The response to P fertilizer was dependent on the rate of N fertilizer applied. The critical bicarbonate extractable soil P level for this soil type, below which pasture responses occurred, was 30 mg/kg at 300N. The critical level at 100N was not reached, but was <23 mg/kg P.

Item Type:Article
Subjects:Agriculture > Agriculture (General) > Soils. Soil science > Soil and crops. Soil-plant relationships. Soil productivity
Agriculture > Agriculture (General) > Fertilisers
Animal culture > Cattle > Dairying
Animal culture > Feeds and feeding. Animal nutrition
Live Archive:27 Mar 2024 01:47
Last Modified:27 Mar 2024 01:47

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