We conducted field trials of rice grown in sandy soil and clay soil to determine the effects of nitrogen application levels on the concentration of NH4＋-N in surface water, loss of ammonia through volatilization from paddy fields, rice production, nitrogen-use efficiency, and nitrogen content in the soil profile. The concentration of NH4＋-N in surface water and the amount of ammonia lost through volatilization increased with increasing nitrogen application level, and peaked at 1-3 d after nitrogen application. Less ammonia was lost via volatilization from clay soil than from sandy soil. The amounts of ammonia lost via volatilization after nitrogen application differed depending on the stage when it was applied, from the highest loss to the lowest： N application to promote tillering 〉 the first N topdressing to promote panicle initiation （applied at the last 4-leaf stage） 〉 basal fertilizer 〉 the second N topdressing to promote panicle initiation （applied at the last 2-leaf stage）. The total loss of ammonia via volatilization from clay soil was 10.49-87.06 kg/hm2, equivalent to 10.92%-21.76% of the nitrogen applied. The total loss of ammonia via volatilization from sandy soil was 11.32-102.43 kg/hm2, equivalent to 11.32%-25.61 % of the nitrogen applied. The amount of ammonia lost via volatilization and the concentration of NH4＋-N in surface water peaked simultaneously after nitrogen application; both showed maxima at the tillering stage with the ratio between them ranging from 23.76% to 33.65%. With the increase in nitrogen application level, rice production and nitrogen accumulation in plants increased, but nitrogen-use efficiency decreased. Rice production and nitrogen accumulation in plants were slightly higher in clay soil than in sandy soil. In the soil, the nitrogen content was the lowest at a depth of 40-50 cm. In any specific soil layer, the soil nitrogen content increased with increasing nitrogen application level, and the soil nitrogen content was higher in clay soil than in sandy s
To investigate the effect of nitrogen （N） level on iron （Fe） content in milled rice, a field experiment was carried out under three N application levels including 0, 150 and 300 kg/hm2 by using 120 rice genotypes. In addition to the genotypic differences of iron content in milled rice, grain yield, 1000-grain weight and N content in grains under the same N level, there were also variations in the response of Fe content in milled rice to N levels. Based on the range and variation coefficient of Fe content in milled rice under the three N levels, the response of Fe content in milled rice to N levels could be classified into four types including highly insensitive, insensitive, sensitive and highly sensitive types. A significant quadratic correlation was found between the Fe content in milled rice and 1000-grain weight or the N content in grains. However, no significant correlation between the Fe content in milled rice and grain yield was detected. In conclusion, there are genotypic differences in the effects of N levels on Fe content in milled rice, which is favorable to breeding of Fe-rich rice under different N environments. Furthermore, high yield and Fe-rich rice could be grown through the regulation of nitrogen on Fe content in milled rice, 1000-grain weight and N content in milled rice.
WEI Hai-yan ZHANG Hong-cheng DAI Qi-gen MA Qun LI Jie ZHANG Qing HUO Zhong-yang Xu Ke
