Rates of dairy shed effluent applied to pastures on clay soils in Northland

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Abstract
Dairy shed washdowns were collected and sprayed on to pasture at two rates over four consecutive milking seasons from 1972 to 1976 on a farm near Whangarei. The high rate of effluent disposal (120 0001/ha every 21 days) increased mean annual herbage yields by 43% and the lower rate of disposal (60 000 1/ha every 21 days) increased yields by 27%. Yield increases were obtained to effluent application throughout each milking season, provided pasture growth was not limited by moisture stress. The responses are mainly attributed to the nutrient content of the effluent since a water-only (60 000 1/ha every 21 days) treatment did not increase herbage yields in any milking season. The nutrie t content and the amounts of nutrients returned in the effluent treatments varied considerably within and between milking seasons. The mean amounts of N, P, and K returned annually in the low rate of effluent disposal were 156, 46, and 348 kg of nutrient/ha. Soil-test levels of K increased significantly (P < 0.05) on plots receiving effluent and although other nutrients such as Ca and Mg also increased, relative to plots receiving water-only, the effects were not always statistically significant. It is concluded that dairy shed effluent is a valuable on-farm source of plant nutrients, capable of substantially increasing herbage yields throughout the milking season and at the same time its application increases the soil K reserves. The results have indicated that effluent can be applied at moderately high rates to Northland clay soils over a number of years without adversely affecting pasture composition or vigour.