Slot-seeding investigations. 4. Effect of phosphate fertilizer and grass suppressant on the establishment and growth of white clover in permanent pasture

White clover (cv. Grasslands Huia) was slot-seeded in April 1982 into plots of permanent pasture of differing botanical composition and reserves of soil phosphate. In one investigation the short-term effects of placing different amounts of phosphate (P₂O₅) in different positions in relation to the slot were investigated. In another, emphasis was given to effects of a grass-suppressing herbicide, propyzamide, on herbage growth and clover contributon during the second year. Fewer seedlings established on plots with a high initial P status and abundant in Holcus lanatus and Alopecurus pratensis than on plots deficient in P₂O₅ and dominated by Agrostis capillaris and Festuca rubra. P₂O₅decreased numbers of establishing clover seedlings when applied in the slots but not when placed beneath them. Growth was increased most when placement was beneath the slot. Application of P₂O₅to plots previously supplied with it resulted in 7.2 g total above ground and 1.7 g stolon dry weight (m row)^?1compared to 1.3 and 0.1 g respectively in plots with low reserves and DO applied P₂O₅. Propyzamide greatly increased the yield and the contribution of clover in the presence of high initial P status and applied P₂O₅. Without propyzamide, clover made only a small contribution until July, averaging 7% for the whole season with little benefit from residual P. Clover growth in late summer was increased from 41 to 292 kg DM ha^?1 where P₂O₅ was applied to P-deficient plots sprayed with propyzamide in the previous autumn. The large increases in clover contribution following propyzamide application were accompanied by small decreases in total seasonal yield of grass. The proportions of H. lanatus and. F. rubra. were decreased and of A. capillaris, increased. Spread of clover from the slots was slow during the first year but was encouraged by both P₂O₅ and propyzamide during the second year. Factors requiring further investigation are discussed.