High phosphorus supply increases persistence and growth of white clover ingrazed dairy pastures during dry summer conditions

Measurements of pasture appearance, white clover leaf and stolon mass, stol on water potential, and percentage clover cover in the sward were made for grazed dairy pastures at Ellinbank, West Gippsland, Victoria, during the ho t, dry month of February 1997. The perennial ryegrass-white clover-based pa stures were in rotationally grazed paddocks from a large farmlet experiment and had received different levels of phosphorus fertiliser (0 or 280 kg P/ ha over an 18-month period), and were being grazed with 2 or 3 cows/ha for the no-phosphorus, or 3 or 4 cows for the high-phosphorus paddocks. Further measurements of white clover composition in the pasture swards were made i n April, following autumn rain. There were marked differences in white clover (i.e. more yellow, flaccid an d desiccated plants with fewer leaves) and pasture appearance (higher frequ ency of patchy, weedy, poorly utilised areas) in the no-phosphorus, compare d with the high-phosphorus treated pastures with the same stocking rate of 3 cows/ha. Also, the high-phosphorus paddocks had a greater white clover pe rcentage than the low-phosphorus paddocks in February with mean percentages of 13.8 and 7.8% respectively. Following rains in March and April, the mea n percentage clover cover in high-phosphorus paddocks had increased substan tially by 30 April 1997 to 30.6% whereas there was a small improvement in m ean clover content in the low-phosphorus paddocks (12.3%). The white clover plants in the high-phosphorus paddocks had heavier stolons, larger leaves and, for the medium stocking rate (3 cows/ha), they appeared to have more l eaves per cm of stolon. The findings support previous studies which have hi ghlighted how high-phosphorus application rates can improve the performance of repeatedly defoliated white clover plants during dry periods.