| Due to its remarkable economic benefits and good ecological benefits,the rice-crayfish co-culture model has become a typical model of comprehensive planting and breeding in paddy fields.In recent years,it has developed rapidly in the rice area of the Yangtze River.During its rapid development,problems such as excessive application of nitrogen fertilizer and difficulty in improving rice yield and quality have emerged.It is of great significance to study the precise application of rice nitrogen fertilizer and its effect on the formation of rice yield and quality under the rice-crayfish co-culture mode to reduce the nitrogen application rate of rice,improve the nitrogen use efficiency,and promote the quality and efficiency of rice in shrimp fields.In this paper,Ezhong 6 and Longliangyou 534 were used as test materials.Under the condition of field experiment,five pure nitrogen fertilization levels were set up,N1(126kg/hm~2),N2(144kg/hm~2),N3(162kg/hm~2),N4(180kg/hm~2)and N0(no nitrogen).The effects of nitrogen application rate on the growth and development,photosynthetic characteristics,grain filling,grain yield and rice quality of rice-crayfish co-culture were studied,and the physiological mechanism of nitrogen application rate affecting the yield and quality formation of rice-crayfish co-culture was analyzed.The main results are as follows:(1)Under the rice-crayfish co-culture mode,the yield change trend of the tested rice was different with the increase of nitrogen application rate.The yield of conventional rice variety Ezhong 6,reaching the highest yield at 162 kg/hm~2(N3)treatment.Continue to increase nitrogen fertilizer(N4),the yield decreased by 5.4%,and the difference between nitrogen fertilizer treatments.According to the analysis of the effect of nitrogen application rate on yield components,the number of grains per panicle and the number of effective panicles were N4>N3>N2>N1>N0,and the grain filling rate was N3>N4>N2>N1>N0.The yield of Longliangyou 534 reached the maximum at N4treatment.The yield of N4 and N3 treatment increased not significantly.The effect of nitrogen application rate on yield components showed that the effective panicle number and grain number per panicle were N4>N3>N2>N1>N0.Therefore,the nitrogen application rate under the rice-crayfish co-cropping mode mainly affects the yield by affecting the number of effective panicles and the number of grains per panicle.Comparing the effects of nitrogen application rate on the yield of planting mode,it can be seen that the yield of rice-crayfish co-cropping rice was higher than that of monoculture rice under the same nitrogen application rate.The average yield of Ezhong6 increased by 1.13 t/hm~2,with an increase of 24.9%.The average yield of Longliangyou534 increased by 0.72 t/hm~2,with an increase of 12.8%.The analysis of yield components showed that the rice-crayfish co-culture mainly increased the number of effective panicles and grain filling rate compared with rice monoculture.The effective panicles and seed setting rate increased by 10.8%and 6.9%respectively,and there was a slight difference between the two varieties.(2)With the increase of nitrogen application rate,the number of tillers,leaf area index,net assimilation rate and net photosynthetic rate increased first and then decreased,and N3 treatment reached the highest value,which was consistent with the trend of yield.The crop growth rate,photosynthetic,leaf area index and SPAD value increased with the increase of nitrogen application rate.With the increase of nitrogen application rate,the average grain filling rate decreased,but the active grain filling period prolonged.The results of the effect of nitrogen application rate on the growth indexes of rice in the two planting modes showed that under the same nitrogen application rate,rice-crayfish co-cropping increased the number of tillers,leaf area index,dry matter accumulation,crop growth rate and photosynthetic compared with rice monoculture.Among the varieties,the tillers number,dry matter accumulation,photosynthetic and net assimilation rate of Longliangyou 534 were higher than those of Ezhong 6.(3)The nitrogen application rate significantly affected the nitrogen use efficiency of rice under the rice-crayfish co-culture mode.With the increase of nitrogen application rate,the nitrogen accumulation of stem sheath,leaf,panicle and plant also increased.In terms of nitrogen transport,the amount of nitrogen transport in rice plants increased with the increase of nitrogen application rate,and the N4 treatment was the largest.The net contribution rate of nitrogen increased first and then decreased with the increase of nitrogen application rate,and the highest was N3 treatment,which was 22.7%,3.9%and4.9%higher than N4,N2 and N1,respectively.By analyzing the nitrogen use efficiency of different nitrogen application treatments,it can be seen that the nitrogen use efficiency and physiological nitrogen use efficiency of each treatment under the rice-shrimp co-culture mode are N1>N2>N3>N4,and the agronomic nitrogen use efficiency is N3>N4>N2>N1.Under the same nitrogen application rate,the nitrogen use efficiency of rice-crayfish intercropping increased by 7.2%on average,the nitrogen absorption efficiency increased by 9.5%on average,and the nitrogen physiological efficiency increased by 3.0%on average.(4)Under the rice-crayfish co-culture mode,with the increase of nitrogen application rate,the appearance quality and taste quality of rice became worse,and the Milling quality was improved.The average chalky grain rate and chalkiness degree of N4treatment were 7.7%and 3.0%,respectively,which were 6.5%,24.6%and 53.0%higher than those of N3,N2 and N1,respectively.Increasing nitrogen fertilizer significantly reduced the amylose content of rice,resulting in a decrease in the taste value of rice,resulting in a decrease in rice quality.By analyzing the key enzymes of starch and protein synthesis,it can be seen that with the increase of nitrogen application rate,the contents of adenosine diphosphate glucose pyrophosphorylase(AGP),starch branching enzyme(SBE),glutamate synthase(GS)and glutamine synthetase(GOGAT)in rice-shrimp co-culture mode have an increasing trend.The analysis of starch RVA profile characteristics showed that with the increase of nitrogen application rate,the peak viscosity,hot paste viscosity,final viscosity and disintegration value decreased,and the setback value increased,which made the starch viscosity characteristics worse and reduced the rice quality.The brown rice rate and milled rice rate of rice showed an upward trend,The highest was N3 treatment,which increased by 0.4%,1.2%and 6.9%compared with N4,N2 and N1,respectively,and improved the milling quality.Comparing the effects of nitrogen application rate on the quality of rice in the two planting mode,it can be seen that the Milling quality,appearance quality and taste quality of rice in the rice-crayfish co-culture mode were better than those in the rice monoculture mode under the same nitrogen application rate,which showed that the milled rice rate increased by 3.7%on average,the chalky grain rate decreased by 8.15%on average,the chalkiness decreased by 6.5%,and the taste value increased by 1.11 on average.This study showed that under the rice-crayfish co-culture mode,with the increase of nitrogen application rate,rice Milling quality was improved,while appearance quality and taste quality decreased.The growth period of rice can maintain higher leaf area index,population growth rate,plant nitrogen uptake,net assimilation rate and longer active filling period,and increase the effective panicle number grain filling rate,.The maximum grain filling rate and average grain filling rate decreased,the grain plumpness increased,the activity of key enzymes in protein synthesis increased,the activity of soluble starch synthase decreased,the protein content increased,the amylose content decreased,and the viscosity of starch RVA decreased. |
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