The N uptake rate in our maize plants (Table 3) was similar to the rates reported in other studies, i.e. 155e300 kg N ha1 [6,45]. The higher uptake rate at higher doses of N suggested some degree of ‘luxury consumption’, but it was observed no differences in the biomass of mature plants treated with PS45 and N300 (Table 3). This could reflect experimental error because the area used for biomass sampling in each plot was smaller (3 m2) compared to that assessed for grain production (23m2)