THE EFFECTS OF RESTRICTING OR STOPPING FERTILISER APPLICATION TO WAIKATO DAIRY PASTURES

Abstract

Waikato dary pastures were developed through large inputs of superphosphate and potassium chloride. Many farmers have continued to apply similarly large amounts of fertiliser in post-development situations. Trials to study the effects on the production of dairy pastures to restricting or stopping fertiliser application were started in 1978 and have continued to the present. The tria1s were conducted on 6 commercial dairy farms throughout the Waikato region selected for high milkfat production and past fertiliser applications. Each trlal included 3 fertiliser treatments: 1000, 500 and 0 kg fertiliser (30% potassic superphosphate)/ha/year. Pasture production was estimated through a trimming technique designed to cause minimal interference with management and use of the experimental paddock by the farmer and in later years through calibrated visual assessments and electronic probe readings of pasture dry matter. Pastures receiving 500 kg fertiliser/ha/year produced on average 2.5% less over an 8 year period than pastures receiving 1,000 kg fertiliser. Applying no fertiliser caused a slow reduction in pasture production in 3 of the trials but an immediate reduction of more than 10% in the other three trials. The latter effect could be partly explained by low soil test levels and high stocking rate. Keywords: Yellow-brown loams, gley soils, maintenance fertiliser, phosphorus, potassium.