THE EFFECTS OF SUB-SEED PLACEMENT OF LIQUID N AND P FERTILIZER ON THE GROWTH AND DEVELOPMENT OF BULB ONIONS OVER A RANGE OF PLANT DENSITIES USING PRIMED AND NON-PRIMED SEED

Phosphates-of-ammonium "starter" fertilizer solution was injected below onion seeds at sowing on a fertile sandy loam soil given basal N, P and K applications. Bulb crops were grown from primed and non-primed seed drilled at six sowing rates to give a threefold range of plant density. Irrigation and nitrogen application were monitored to ensure that plants remained unstressed throughout growth. The starter fertilizer resulted in increased P and N and reduced K content during seedling growth. In both an early-sown and a late-sown experiment, shoot growth was accelerated by starter fertilizer and shoots became approximately 50% heavier than those without starter. Growth curves showed that this was equivalent to a 3-3.5 d advancement of growth. Starter fertilizers resulted in 1-2.5 d advancement of crop maturity as shown by the date of 50% foliage fall-down. In the later sown experiment, starter fertilizer reduced the percentage of non-maturing 'thick-necked' bulbs. Bulb yields were not significantly increased by starter fertiliser. Data showing similar enhancements of seedling growth on other soils are also discussed. Seed priming advanced the date of seedling emergence but had no significant effects subsequently. Increases in plant density advanced the date of crop maturity and increased total bulb yields.