Grain quality of flooded rice is affected by season, nitrogen rate, and plant type

Quality of grain, next to yield, is the most important factor for rice (Ory za sativa L.) production in semiarid tropical Australia. Studies were under taken in the Burdekin River Irrigation Area of northern Australia to improv e rice grain quality through nitrogen fertilisation. This paper reports the results of 4 experiments comparing the response of 3 rice genotypes differ ing in maturity and stature to 5 rates of applied nitrogen (0, 70, 140, 210 , and 280 kg/ha) over 4 seasons (2 wet and 2 dry seasons). The components o f grain quality studied were endosperm chalkiness, whole grain millout, gra in size, alkali digestion (gelatinisation temperature), and grain protein. This paper also examines the suitability of the 3 genotypes as parental mat erial in breeding programs aimed at selecting for specific grain quality at tributes. Starbonnet was identified as a potential parent in breeding programs which aim to specifically select for reduced chalkiness and high millout in low N environments. Selection for lower chalkiness, and higher millout and prote in concentration, should occur in a wide range of target environments to ac count for the seasonal variation observed in these parameters. Grain size a ppeared to be affected more by genetic than agronomic factors, since grain length and breadth were largely unaffected by N rate, yet genotypic differe nces were found for both parameters in all experiments. Newbonnet grain was long and slender, suggesting this genotype would be a suitable parent in b reeding programs aimed at improving grain appearance. The response of alkal i digestion to N rate and genotype was small for all seasons. The importance of developing N fertiliser strategies that optimise both gra in yield and quality was highlighted by differences in the responses of gra in protein and grain yield to N rate. A number of linkages were examined am ong various components of grain quality. However, the magnitude of these li nkages was small, suggesting that selection for one quality component shoul d not be at the expense of selection for another.