Effects Of Nitrogen Fertilizer Management On Cadmium Accumulation In Double-season Rice And Its Regulation Mechanism

In order to study the effect of nitrogen fertilizer management on the accumulation of cadmium in rice and explore the mechanism of nitrogen reduction by cadmium,the early rice varieties Zhuliangyou 819 and Luliangyou 996,the late rice varieties Xiangwanxian 12and Yuzhenxiang were selected as test materials in 2018.Community trials were conducted in Huayuan Village,Yanxi Town,Liuyang City,Hunan Province,and Tongxin Village,Fulin Town,Changsha County,Hunan Province.In experiment 1,three basic top dressing ratios were set with nitrogen application rate of 180kg/hm2 during the whole growth period of rice,treatment 1,4:4:2:0(T1),treatment 2,8:0:2:0(T2),Treatment 3,6:0:2:2(T3),no nitrogen application(CK)during the whole growth period of the control;Experiment 2,the nitrogen application rate during the whole growth period of rice was 180kg/hm2,and the application rate of grain fertilizer was 20%%Of the three grain fertilizer application periods,the ratio of basal top dressing is 6:0:2:2,treatment 1,grain fertilizer(F1)at the earing stage,treatment2,grain fertilizer(F2)at the full ear stage(F2)and treatment 3,filling stage Fertilizer application(F3),and the control,no nitrogen application(CK)during the whole growth period.The main findings are as follows:1.The application of nitrogen fertilizer increased the yield of rice and the accumulation of dry matter.The yield of early and late rice under the treatment of the proportion of top dressing increased 19.3%～91.5%and 2.9%～37.30%respectively compared to the treatment without fertilization.The yield reached the highest at 8:0:2:0,which was 491.56g/m~2.The yields of the two varieties of early rice Luliangyou 996 and late rice were highest at the ratio 6:0:2:2,respectively 520.28 g/m~2,855.16 g/m~2,1053.66 g/m~2,the yield of topdressing grain fertilizer treatment at the initial heading stage,full heading stage and filling stage was also significantly increased compared to the non-nitrogen treatment;the ratio of each base topdressing fertilizer was 6:0:2:2.The high dry matter accumulation in each period shows that under the condition of proper nitrogen application to ensure fertility and fertilization,the application of grain fertilizer at different periods according to the characteristics of rice varieties is conducive to rice yield and dry matter improvement.2.The effects of basal top dressing ratio and application period of grain fertilizer on rice cadmium accumulation and the transfer coefficient of cadmium in plants are significantly different,and there are differences in location.The accumulation rules of cadmium in rice are different.The cadmium content and cadmium accumulation are shown in the mature stage>milk mature stage>tillering stage,and the roots>stems>leaves(stems and leaves)>brown rice.As far as the maturity of brown rice in the two regions is concerned:the early rice plants Liangyou 819 and Luliangyou 996 planted in the Liuyang area had the lowest cadmium content of 0.067 when the ratio was 8:0:2:0 and 6:0:2:2,respectively.mg/kg and0.087mg/kg,the late rice Xiangwanxian 12 hao and Yuzhenxiang had the lowest cadmium content at the ratio of 4:4:2:0 and 6:0:2:2,0.089 mg/kg and 0.141mg/kg,respectively;the early rice plant Liangyou 819 planted in Fulin area had the lowest cadmium content at the ratio of 6:0:2:2,which was 0.172 mg/kg.The lowest cadmium content was 0.179 mg/kg and 0.384 mg/kg,respectively,and the application of grain fertilizer could significantly reduce the cadmium content of brown rice at the mature stage of double-cropping rice in Liuyang area and early rice in Fulin area.The cadmium content of brown rice was significantly reduced under the treatment of grain fertilizer in different periods,but the difference between the treatment with grain fertilizer and the treatment with no nitrogen treatment reached a significant level only at the filling stage,while the application of grain fertilizer at the full panicle stage significantly increased the cadmium content of brown rice.Therefore,formulating a reasonable ratio of basic top dressing according to different rice genotypes and soil types can help reduce the accumulation of cadmium in rice.3.Root surface iron film formation(expressed as DCB-Fe content)of early rice Zhuliangyou 819 and late rice Xiangwanxian 12 was expressed as tillering stage>milk maturity stage,while early rice Luliangyou 996 and late rice Yuzhenxiang showed tillering stage Period<milk maturity period;basal top dressing ratio/grain fertilizer application period has a significant effect on the accumulation of manganese,cadmium and cadmium accumulation in rice root surface iron film at different growth stages,but there are differences between varieties.The early rice Zhuliangyou 819 and the late rice two varieties had negative correlations in the root surface manganese content,iron content and cadmium content,and the early rice Luliangyou 996 root surface had a positive correlation between manganese and iron content and cadmium content;The accumulation of cadmium in the surface iron film of the early rice Zhuliangyou 819 and the late rice Yuzhenxiang was increased,and the accumulation of cadmium in the root surface iron film of the cadmium early rice Luliangyou 996 and late rice Xiangwanxian 12 was decreased.4.From the perspective of the accumulation of cadmium by the subcellular components,the cadmium content of different components of different organs is different in nitrogen treatment,in which the roots and leaves show cell walls>soluble parts>organelles,and the stem show cell walls>organelles>soluble In part,compared with roots,the distribution ratio of cadmium in the above-ground part of subcellular components is more susceptible to nitrogen,Nitrogen application can improve the separation effect of the cell wall on the fixed or soluble part of cadmium;It can improve the fixation and compartmentalization of cadmium in the cell wall and soluble parts of rice leaves.