Effects of nitrogen top-dressing on starch gelatinization and retrogradation properties of spring and autumn waxy maize at the jointing stage

To understand the effects of nitrogen top-dressing amounts on starch gelatinization and retrogradation properties of spring and autumn sown waxy maize at the jointing stage, a study was carried out at the Experiment Farm of Yangzhou University in 2008. There were three cultivars (Suyunuo 5, Kennian 1 and Suyunuo 1) and three nitrogen top-dressing amounts (0, 150 and 300 kg/ha) in the study. The results show the main waxy maize starch gelatinization and retrogradation properties are significantly affected by the single factor and interactions between the nitrogen top-dressing amount at the jointing stage, sowing date and cultivar. In general, the gelatinization and retrogradation characteristics are better under the N 150 kg/ha nitrogen top-dressing amount and the autumn-sowing condition, especially for the cultivar Kennian 1, that is the raw starch has a lower peak temperature (Tp), higher enthalpy of gelatinization (ΔHgel) and low percentage of retrogradation (%R). Results of the correlation analysis indicate that the percentage of retrogradation is positively correlated with enthalpy of retrogradation (ΔHret) (r= 0.82, Pc (r= 0.47, Pgel is positively correlated with peak height index (PHI)(r= 0.53, Pp (r= -0.53, Pc of retrograded starch(r= -0.52, Pret is positively correlated with though onset temperature (To) of retrograded starch (r= 0.46, P< 0.05) and PHI of retrograded starch (r= 0.66, P<0.01). Considering the starch gelatinization and retrogradation properties in different treatments, the autumn sowing waxy maize cultivars and the N 150 kg/ha nitrogen top-dressing amount at jointing stage are suitable to get better starch.