In both years, a 1.5 m segment of each row was randomly cut at ground level from each plot just prior to harvest. These samples were used to determine biomass, after drying at 50 °C for 48 h, and grain yield. Final grain yield was also obtained at maturity by harvesting each 10.0 m × 1.8 m plot with a Kew experimental plot header. Grain protein concentration was determined by NIR reflectance. The trial was harvested 145 DAS in 2006 and 154 DAS in 2007. Data were analysed by ANOVA.
The amount of N harvested in the grain protein was calculated from yield and grain protein content, using a conversion factor of protein content of 5.61 times amino acid N content [8]. N in protein was used rather than total grain N (which is about 1.05 times higher) because commercial prices are based on protein content. The Mitscherlich diminishing returns function,