Phosphorus seed coatings for pasture species. I. Effect of source and rate of phosphorus on emergence and early growth of phalaris (Phalaris aquatica L.) and lucerne (Medicago sativa L.)

Abstract

Seed coatings containing phosphorus (P) can be an effective way of promoting early seedling growth in P-deficient soil, but there is insufficient information available on the P sources and rates which are both safe to germinating seeds and effective in supplying P. A growth chamber experiment was undertaken to study the effect on the emergence and early growth of phalaris (Phalaris aquatica L.) and lucerne (Medicago sativa L.) of seed coatings containing one of three P sources (mono-[MCP], di-[DCP], or tricalcium phosphate [TCP]) at three rates (0.625, 1.25 or 2.5 mg P seed-1). The emergence of lucerne was markedly delayed (as measured by fitted Mitscherlich functions) by increasing rates of MCP, whilst that of phalaris was only slightly delayed. DCP and TCP had only slight effects on the emergence of both species. Leaf number (at 27 days after sowing [d.a.s.]), dry matter yield and P content of shoots of both species (at 35 d.a.s.) were increased by all P sources. With phalaris, MCP was approximately four times as effective per unit of P as DCP, which in turn was approximately four times as effective as TCP, whereas, with lucerne, MCP was twice as effective as DCP, which in turn was twice as effective as TCP. The results show that whilst emergence was most affected by soluble P sources at high rates, these same sources were most effective in promoting early P uptake per unit of P applied.