Influences Of Different Types And Amounts Of Nitrogen Fertilizer On Yield And Cadmium Accumulation In Rice

In recent years,cadmium pollution has become one of the most concerned issues for the general public.The problem of food safety caused by cadmium pollution has also received widespread attention.However,high rice yield and low cadmium in brown rice are currently difficult problems.We carried out studies on rice yield and cadmium uptake with different types and amounts of nitrogen fertilizers,in order to explore the effects of different types and amounts of nitrogen fertilizers on rice yield and cadmium uptake.In this paper,Zhongzao39and Xiangwanxian13hao were selected as experimental materials for the early and late rice,respectively,and pot experiments were conducted at the Rice Research Institute of Hunan Agricultural University in 2017.A total of 9 different nitrogen fertilizer types and dosage treatments(N1-N9)and one non-nitrogen treatment(N0)were applied.The types and amount of nitrogen fertilizers were:sodium nitrate containing 2.5,5,and 7.5 g nitrogen per pot(N1-N3),urea containing 2.5,5,and 7.5 g nitrogen per pot(N4-N6),ammonium bicarbonate containing 2.5,5,and 7.5 g nitrogen per pot(N7-N9).The main results are as follows:1.Nitrogen application could increase rice yield.The nitrogen application had a higher yield of 2.09%-63.09%than the non-nitrogen treatment in early rice,and nitrogen application in late rice had a significantly higher yield of 23.84%-85.40%than the non-fertilizer treatment.Among the different types of nitrogen fertilizers,ammonium nitrogen had the most significant effect on increasing rice yield,which was expressed as:ammonium nitrogen>urea>nitrate nitrogen,and both early rice and late rice had the highest yield with ammonium nitrogen containing 5g nitrogen per pot.They were 182.32 g per pot and 293.47g per pot,respectively.The effects of various nitrogen fertilizers on yields showed a trend of increasing first and then decreasing with the increase of nitrogen application rate,indicating that there was a suitable value for the application of nitrogen fertilizers,and too much or too little was not conducive to obtaining high yields.In this experiment,the best yield increase effect is to use ammonium nitrogen containing 5g nitrogen per pot.2.The application of nitrogen fertilizer can also increase the biological yield of rice,and was significantly higher than that of no nitrogen treatment.With the increase of nitrogen application rate,the total dry matter weight of plants and dry matter weight of each organ also showed an increasing trend.The accumulation of roots and stems in the mature period of early rice were all highest with 5 g nitrate nitrogen applied per pot,which were 513.75g/m~2and 2311.89 g/m~2 respectively.The dry matter weight of leaves and grain under the condition of 5g of ammonium nitrogen applied to each pot was 679.73g/m~2 and 623.34g/m~2,respectively.The root and stem dry weight of late rice was the highest with 7.5g ammonium nitrogen(N9),which were 436.77g/m~2、1965.46g/m~2 respectively.The accumulation of dry matter in grains all increased first and then decreased with the increase of nitrogen application rate,indicating that the amount of nitrogen applied had a critical value for dry matter accumulation.Exceeding the critical value not only did not increase dry matter accumulation,but also reduced dry matter.There was no significant difference in root and stem weight at different stages of early and late rice.3.The rules of cadmium uptake of different organs in different periods were different.The application of ammonium nitrogen could effectively reduce the cadmium content in vegetative organs of early rice in different stages.The cadmium content in roots,stems,and leaves of N9 at the heading stage was the lowest,which was 1.30 mg/kg,0.22 mg/kg,and0.12 mg/kg,respectively.Urea can reduce cadmium content in vegetative organs of late rice,and is significantly lower than that of nitrate nitrogen and no fertilizer application.Different nitrogen fertilizers showed a decreasing trend in cadmium content in different parts of different periods with increasing nitrogen application rates,indicating that appropriate increase in nitrogen application rate can reduce the absorption of cadmium by rice.In rice brown rice,chromium>plumbum>arsenic>cadmium existed among the contents of various metal elements,and the correlation among other metal elements was not significant.The accumulation of chromium,arsenic,cadmium,and plumbum in non-fertilizer-treated brown rice was the least.With the increase of nitrogen application rate,the accumulation of cadmium in brown rice decreased with nitrate nitrogen treatment.Ammonium nitrogen could reduce the accumulation of cadmium in rice brown rice under a certain nitrogen application rate.The rules of cadmium uptake in different organs of rice were different,the result of different organ showed:roots>stem>leaves>brown rice in each organ,which means cadmium is mainly absorbed from the root system and enters brown rice after passing through stems and leaves.Therefore,the appropriate amount of ammonium nitrogen can reduce the accumulation of cadmium in rice brown rice.