Pasture response to superphosphate applied at different times

DM yields from a ryegrass-white clover pasture on a low P-fixing (P retention 23%) yellow-grey to yellow-brown earth intergrade soil were measured after annual applications of superphosphate in March, May, July, September, November, or January over 6 years. Phosphate was applied at 9.5 and 28.5 kg P/ha. The effects of these treatments were examined under initially high and low P-test levels (Truog values of 8.1 and 3.1 respectively). Results indicate that although time of application typically resulted in about 4% differences in annual yields, this time can be used to manipulate the balance of seasonal yields. In particular, it can result in up to 8% difference in autumn yields, application in July being most favourable. This effect is much reduced with initial high P-test and the higher level of annual application. These results could be helpful to the fertiliser industry in encouraging a more even spread of demand through the year.