Interaction between Polymer Coated Nitrogen Fertilisers and Rainfall on Vegetative Growth versus Ripening

paper only the treatments receiving commercial urea prills Using maize as the indicator crop for recently tilled soils over seven successive seasons, urea prills coated with 0,5% polymer gave the greatest grain yield increases over commercial urea in seasons of below average rainfall (3,3 tonsha versus 1,6 tonsha in 1989-90). The ratios of grain to stover were also higher. In wet years, no differences were recorded. The concentrations of Ca and Mg in the leaves were also higher in the drier seasons and were strongly correlated with the increased grain yields (r = +0,8933 and +0,8922 respectively). In trials with ratoon cane on untilled soils, the polymer coated urea and LAN treatments (both at 0,5%) gave the expected higher ers % cane values (NS) than their commercial equivalents in seasons of normal and high rainfall, but not in a drought season. The variable responses in tons caneha induced by the coated fertilisers, together with the chemical compositions of leaf and soil samples, suggest that thinner polymer coatings are required for ratoon cane.