Abstract:

Studies on the effects of four different nitrogen application levels (zero, low, medium, and high) on yield, quality, and edible safety (Hg, As, Cd concentrations in rice grains) were carried out under field conditions with Gui xiaozhan, a high quality rice, as tested material. The results showed that when the nitrogen application was below 150 kg/hm2, with the enhancement of nitrogen application, the panicle per unit area significantly increased so as to enhance the rice yield, but the rice yield insignificantly improved when the nitrogen application was over 150 kg/hm2. As the increase of nitrogen application, the brown rice rate, milled rice rate, head rice rate, and protein content were improved, although the chalky grains percentage, chalkiness percentage, amylase content, and gel consistency decreased. Among them, the difference of brown rice rate, milled rice rate, and head rice rate between low, medium, and high nitrogen level was not significant, and they were all significantly higher than the treatment of zero nitrogen fertilizer application. There was no significant difference in chalky grains percentage and chalkiness percentage between medium and high nitrogen level, and they were all significantly lower than the treatment of low nitrogen fertilizer application. The protein content, amylase content, and gel consistency differed dramatically between different nitrogen application levels, and the difference reached to the 0.05 significant level. The results indicated that increasing nitrogen amounts had little effect on Hg concentration in rice, but it could result in increasing content of As and Cd. Among them, the difference in Cd concentration between medium and high nitrogen level was significant, and there was significant difference in As concentration between each nitrogen application treatment. Under this experiment condition, a proper amount of N application was beneficial to increase the rice yield, and improve the rice quality to a higher level. By reducing nitrogen fertilizer, As, Cd absorption and concentration in rice could be minimized, and edible safety could also be improved. The nitrogen fertilizer should be applied properly during high quality rice cultivation, but the nitrogen application rate should not be more than 150 kg/hm2.