Effects Of Nitrogen Fertilizer On The Content Of Cadmium And Main Mineral Nutrients In Brown Rice Of Double-cropping Rice

Cadmium(Cd)is a kind of heavy metal element with high biological toxicity,high mobility and wide distribution.Cd pollution affects the growth and development of crops,and enters the human body through the food chain,endangering human health.Rice is one of the bulk grains with the strongest Cd absorption capacity.Prevention and control of rice Cd pollution are of great significance to ensure food safety in China.Nitrogen(N)is one of the essential elements for plant growth.The application of nitrogen fertilizer can regulate the transport process of Cd in plants.In this experiment,it included four nitrogen fertilizer ratios:5:5:0:0(T1),4:4:2:0(T2),6:0:2:2(T3),3:2:2:3(T4)and no nitrogen treatment(CK).a pot experiment was conducted to study the effects of nitrogen fertilizer on the Fe,Mn,and Cd contents on root plaque of double-cropping rice and the contents of Cd,Cu,Fe,Mn,and Zn in double cropping rice.The main results are as follows:1.The application of nitrogen fertilizer increased the contents of Cu,Fe,Mn,and Zn in brown rice of double-cropping rice,and the overall performance of late rice was late rice >early rice.The Cu content of late rice Xiangwanxian 13 hao was significantly increased by16.71% and 87.53%,and the contents of Cu and Fe in brown rice of late rice Yuzhenxiang were significantly increased by 32.61%-55.71% and 50.38%-105.57%,respectively.The effect of nitrogen fertilizer on the Cd content of brown rice was significantly different in varieties and seasons.Under T2 and T4 treatments,The Cd content of early rice Taiyou 368 was significantly decreased by 55.32% and 51.06%,respectively.The application of nitrogen fertilizer had the risk of increasing the Cd content of Xiangzaoxian 32 hao brown rice,it was significantly increased by 85.37% and 51.22% under T1 and T2 treatments,respectively,and decreased by 9.76% and 14.63% under T3 and T4 treatments,respectively.Under nitrogen treatment,the Cd content in brown rice of the late rice Xiangwanxian 13 hao was decreased by 13.04% and 47.83%,the Cd content of Yuzhenxiang brown rice was significantly decreased by 11.11% and 44.44%,respectively,and the Cd content of brown rice of two varieties was the lowest under T3 treatment.2.Application of nitrogen fertilizer increased Fe and Mn transport from stems and leaves to brown rice,decreased Cd transport from stems and leaves to brown rice,and had no significant indigenous effect on Cu and Zn transport.Cd and mineral elements in roots,stems,and leaves of early rice had no good correlation with Cd and mineral elements in brown rice,but there was a positive correlation between Cd content and Cu and Fe content,Cu content,Fe and Mn content in early rice brown rice.Mn in stems and leaves of late rice was negatively correlated with Cd in brown rice and positively correlated with Cu,Fe,Mn,and Zn in brown rice.There was a negative correlation between Cd content and Cu,Mn,and Zn content in late brown rice,and a significantly positive correlation between Cu,Fe,Mn,and Zn content.3.The Fe content on root plaque of early rice at different growth stages showed full heading stage > booting stage > mature stage,the Mn and Cd contents on root plaque showed booting stage > full heading stage > mature stage,and the Fe and Cd contents o on root plaque of late rice showed mature stage > booting stage.Overall,the application of nitrogen fertilizer reduced the Fe content on root plaque of early rice Taiyou 398 and late rice at booting stage,had no significant effect on the Mn content on root plaque of early rice,increased the Mn content on root plaque of late rice Yuzhenxiang at the booting stage,and significantly increased the Cd content on root plaque of early rice Taiyou 398 at the maturity and late rice at booting stage.There was a significant negative correlation between the Cd contents on root plaque at booting stage of double-cropping rice and the Cd content in brown rice.In summary,the application of nitrogen fertilizer could promote the adsorption of Cd by root membrane at the booting stage and inhibit the accumulation of Cd in brown rice.The application of nitrogen fertilizer could increase the transport of Cu,Fe,Mn,and Zn to grain and antagonize the transport of Cd to brown rice.It is suggested that in the actual production,the demand for nutrients in the early growth stage of rice should be met,supplemented by the application of essential mineral nutrient fertilizers for rice to reduce Cd accumulation in rice.An appropriate amount of nitrogen was applied after the full heading stage to maintain a certain level of nitrogen in plants,slow down leaf senescence,prolong grain filling time,and inhibit the migration of Cd in tissues to grains,the pursuit to harvest rice with lower Cd content.