| Rice plays a very important role in China’s grain production.Sufficient supply of nitrogen fertilizer is one of the important measures to improve rice yield.However,the nitrogen use efficiency of paddy field in China is low,only between 20%and 35%.The low utilization rate of nitrogen fertilizer in China was due to high nitrogen application amount,improper choice of nitrogen fertilizer types and application methods,and the neglect of comprehensive application of nutrient management and cultivation techniques.The requirements for soil nitrogen supply level vary in rice with different yield production through the whole growth period.In order to realize better fertilization,it is critical to understand the transformation rules and influencing factors different kinds of nitrogen fertilizer with different application methods.This paper compared the transformation rules of different kinds of nitrogen fertilizers through pot incubation and simulation experiments.The effects of different application methods and dosage on rice growth and soil available nitrogen followed the one-time basal application of loss-control urea were also investigated-The aim was to provide scientific references for increasing rice nitrogen use efficiency,simplifying cultivation practices and reducing non-point source pollution in agriculture.1.In this paper,six nitrogen application rates(0,100,200,300,400,500 mgN kg-1)were set up in the laboratory incubation experiment.Two types of nitrogen fertilizers(ammonium sulfate and urea)were mixt with soils at the above mentioned rates,incubated at 25℃ with 60%field water capacity for 56 days.The contents of NH4+-N,NO3--N and alkali hydrolyzable nitrogen were determined at 0,3,7,14,28,56 d.The content of soil fixed ammonium was determined at 7 d and 56 d.The transformation rules of two kinds of nitrogen fertilizers in paddy soil were studied,and the effects of urea and ammonium sulfate on nitrogen forms and nitrification in paddy soil under different nitrogen application rates were clarified.The main results are as follows:The contents of NH4+-N,NO3--N,alkali hydrolyzable nitrogen in soil increased,while the content of fixed ammonium first increased and then decreased with the increase of nitrogen application rate at the same culture time.At day 7,the content of fixed ammonium was the highest in treatment N3(300 mg N kg-1)for both fertilizers.At day 7,the highest fixed ammonium content was the highest in N4(400 mg N kg-1)treated with ammonium sulfate,while the content of fixed ammonium was the highest in N3(300 mg N·kg-1)treated with urea.The contents of fixed ammonium in urea treatment was higher than those in ammonium sulfate treatment,except for N5.The highest nitrification rate was found in N2(200 mg N·kg-1)for ammonium sulfate and urea treatments,and the nitrification of urea-treatment soil was higher than that of ammonium sulfate of the same nitrogen level and different nitrogen application methods.The apparent loss of inorganic nitrogen(including fixed ammonium)in ammonium sulfate treatment was higher than that in urea treatment,with the lowest apparent loss found in soils treated with 200～300 mg N kg-1 urea.The results demonstrated that the accumulation of NH4+-N lasted for a long time in the process of cultivation.2.Pot experiment was carried out in 2019 and 2020 with Nanjing 3908 as test material under the condition of one-time basal urea application,and 20 kg soil per pot.six nitrogen application rates were 0(NO),5.17(N20),11.43(N40),17.14(N60),22.85(N80),28.58(N100)g/pot loss control urea and two fertilization methods(side deep fertilization and full layer fertilization)were set up in 2019.Five nitrogen application rates were 0(NO),2.86(N10),4.29(N15),5.17(N20),11.43(N40)g/pot and two fertilization methods(side deep fertilization and full layer fertilization)were set up in 2020.The physiological index,yield index,plant nutrient absorption index and soil available nitrogen content of rice were determined to clear the effects of different nitrogen application rates on rice growth and soil available nitrogen.the main results are as follows:(1)From the aspect of yield analysis,under the two fertilization methods,one-time basal application of loss control urea achieved high yield at N40-N60.the one-time deep base application of urea loss control is more suitable for the lower than N40.In the actual production process,the side deep fertilization technology should be recommended when the control of nitrogen and nitrogen reduction are advocated.The effective panicles,grains per panicle,primary branches and secondary branches per unit area were increased by increasing the loss-control urea rate,which lead to increasing yield and income;the final panicle rate and dry matter weight of lateral deep fertilization were lower than that of full layer fertilization at the same nitrogen level,but the difference was not significant.(2)The increase of loss control urea application rate was beneficial for the increase of SPAD value,preventing premature senescence of effective leaves,promoting photosynthesis,improving dry matter accumulation of rice,and then increasing grain yield.There was no significant difference between the two fertilization methods.(3)Nitrate reductase(NR)activity of flag leaf of rice was the highest at tillering stage,and increased with the increase of nitrogen application rate,and there was no significant difference between the two fertilization methods.From the correlation coefficient of nitrogen metabolism enzyme activity and yield,Under the condition of one-time basal application of controlled loss urea,nitrate reductase(NR)activity of flag leaf at tillering stage was significantly positively correlated with yield,nitrate reductase(NR)activity at jointing stage and grain filling stage was significantly negatively correlated with yield;Glutamine synthetase(GS)activity of flag leaf at tillering stage was negatively correlated with yield,and glutamine synthetase(GS)activity of flag leaf at jointing stage,heading stage and grain filling stage was positively correlated with yield,only at heading stage reached significant level glutamine synthetase GS activity had no significant effect on rice yield at growth stage,and there was a positive correlation between flag leaf glutamate synthase(GOGAT)activity and rice yield at all growth stages,especially at grain filling stage.(4)The physiological and agronomic use efficiency of nitrogen fertilizer increased first and then decreased with the increase of nitrogen application rate of loss control urea,and the partial productivity of nitrogen fertilizer decreased with the increase of nitrogen application rate.In 2019,the nitrogen physiological utilization rate,Nitrogen agronomic utilization rate and nitrogen partial productivity of lateral deep fertilization treatment were higher than that of full layer fertilization treatment with nitrogen application rates were at N20～N40,N100,but the lateral deep fertilization treatment were lower than that of full layer fertilization treatment with the nitrogen application rates were at N60～N80.(5)Under the N40,N60 nitrogen application level,the nitrogen absorption capacity of plants was high,which reduced the accumulation of nitrate nitrogen in the soil and the leaching risk of nitrate nitrogen. |
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