Effects Of Nitrogen Application Rate On Lodging Resistance And Yield Of Direct Seeding Shrimp-rice

Shrimp-rice comprehensive planting and breeding model is an important model of agricultural production in Hubei Province and even the southern rice region.Due to the influence of long-term soil flooding and fertility,lodging has become an important factor affecting the yield of direct seeding shrimp-rice.Taking typical shrimp-rice varieties Yuzhenxiang,Huanghuazhan,Efengsimiao and Xiadaoyihao as materials and no fertilization as control,three split plot experiments with nitrogen application levels(120,150 and 180kg·hm^-2)were set to study the effects of different nitrogen application levels on the lodging resistance,lodging resistance、yield and quality of direct seeding shrimp-rice under the continuous cropping mode of shrimp-rice.The main results are as follows:（1）On the stem morphology,the effect of nitrogen application rate on lodging resistance of shrimp-rice showed that the plant height of shrimp-rice,the height of gravity center on the 19th and 26th days after full heading,and the length of the 4th and 5th internode from the top increased significantly with the increase of nitrogen application rate.Compared with the control,nitrogen application can increase plant height,height of center of gravity on the 19th and 26th days after full heading,length of the 4th and 5th internode from the top by 2.00%～6.28%,3.47%～9.07%,2.11%～8.05%,9.77%～23.77%,19.23%～53.79%（2020）and 2.05%～6.56%,3.78%～9.64%,2.25%～8.27%,7.27%～22.92%,15.33%～46.45%（2021）.（2）On the terms of mechanical properties,the effect of nitrogen application rate on lodging resistance of shrimp-rice showed that the breaking moment of the 4th and 5th internode of shrimp-rice increased first and then decreased with the increase of nitrogen application rate,among which Yuzhenxiang,Huanghuazhan,Xiadaoyihao N2 treatment and Efengsimiao N1 treatment were the largest;The lodging index decreased first and then increased,among which Yuzhenxiang,Huanghuazhan and Xiadaoyihao were treated with N2,and Efengsimiao N1 was the smallest.The bending moment of the 4th and 5th internode from the top increased significantly with the increase of nitrogen application.（3）On the section structure,the effect of nitrogen application rate on lodging resistance of shrimp-rice showed that the vascular bundle area of the 4th and 5th internode from the top increased first and then decreased with the increase of nitrogen application rate,among which Yuzhenxiang,Huanghuazhan,Xiadaoyihao N2 treatment and Efengsimiao N1 treatment were the largest;The thickness of stem wall and the number of large and small vascular bundles in the top 4th and 5th internodes increased significantly with the increase of nitrogen application.（4）On the terms of chemical composition,the effect of nitrogen application rate on lodging resistance of shrimp-rice showed that the content of soluble sugar and starch of the 4th and 5th internode from the top main stem increased first and then decreased with the increase of nitrogen application rate,among which Yuzhenxiang N1 treatment,Huanghuazhan,Efengsimiao and Xiadaoyihao N2 treatment were the largest.（5）The effect of nitrogen application rate on the yield of shrimp-rice showed that the yield increased first and then decreased with the increase of nitrogen application rate.Among the yield components,the number of effective panicles increased with the increase of nitrogen application,and the number of grains per panicle,seed setting rate and 1000 grain weight increased first and then decreased with the increase of nitrogen application.Among them,the yield of Yuzhenxiang is the highest under the N1 level of nitrogen application rate treatment,and the two-year yield is 8.99 t·hm^-2（2020）and 9.52t·hm^-2（2021）respectively,which is 41.92%,12.35%,21.23%（2020）and 35.61%,8.64%and 18.34%（2021）higher than that of N0,N2 and N3;Huanghuazhan,Efengsimiao and Xiadaoyihao had the highest yield under the nitrogen application treatment N2 level,reaching 10.10t·hm^-2,8.95t·hm^-2,10.05t·hm^-2（2020）and 10.22t·hm^-2,9.29t·hm^-2 and10.12t·hm^-2（2021）respectively,and Huanghuazhan N2 was 43.28%,23.92%,8.19%（2020）and 44.79%,16.95%and 7.16%（2021）,Efengsimiao N2 was 29.05%,14.48%higher than N0,N1 and N3 2.01%（2020）and 30.92%,15.03%and 2.37%（2021）.The N2 content of Efengsimiao was 38.18%,16.21%,5.35%（2020）and 30.60%,10.12%and5.25%（2021）higher than that of N0,N1 and N3,and the difference was very significant.（6）The effect of nitrogen application rate on rice quality showed that with the increase of nitrogen application rate,the brown rice rate,milled rice rate,whole milled rice,chalky grain rate,chalkiness,length width ratio and amylose content rate of rice increased first and then decreased.Among them,Yuzhenxiang processing quality and appearance quality N1 treatment,Huanghuazhan,Efengsimiao,Xiadaoyihao processing quality and appearance quality N2 were the highest,Yuzhenxiang and Huanghuazhan physical and chemical quality N1 treatment,The N2 treatment of Efengsimiao and Xiadaoyihao was the highest.In conclusion,the amount of nitrogen application affects the population construction of direct seeding shrimp-rice by affecting the elongation,plant height,center of gravity height and tillering panicle of the 4th and 5th internode from the top of the main stem of shrimp-rice,and has an impact on the lodging resistance,yield and rice quality.Appropriate nitrogen reduction is an effective measure to improve the lodging resistance,high and stable yield and quality of shrimp-rice.In view of the differences in lodging resistance and fertilizer tolerance of different shrimp-rice varieties,nitrogen fertilizer should be applied reasonably in combination with the characteristics of varieties in production to reduce the risk of lodging and improve yield and quality.The reasonable nitrogen application rate of Yuzhenxiang is 120kg·hm^-2;The reasonable nitrogen application rate of Huanghuazhan and Xiadaoyihao is 150kg·hm^-2;The reasonable nitrogen application rate of Efengsimiao can be 120～150kg·hm^-2.