Study On The Formation Mechanism Of Hierarchical Difference In Wheat Yield After Rice Stubble In Jiangsu Province

With the increasing attention paid to the means of increasing the crop yield by reducing the yield difference in different regions,China has gradually begun to study the yield difference in recent years.The middle and low reaches of the Yangtze River are the main wheat producing areas for rice stubble in China.It is of great significance for the production and development of wheat in China at the present stage to study the yield difference to understand the level of regional yield difference,to explore the mechanism of the formation of yield difference,and finally to come up effective solutions of reducing the yield difference.In this study,three major rice-stubble and wheat-producing provinces in the middle and low reaches of the Yangtze River were taken as research targets to understand the level of regional yield difference.A serial of experiments were set up in two typical ecological regions of Jiangsu Province according to the results of the investigation to explore the differences in population traits,individual traits and other aspects of rice-stubble and wheat at different yield levels,The main characteristic differences in the formation process of yield levels were identified,which provided the scientific basis for the subsequent search for limiting factors and proposing means to reduce the difference.The main results are as follows:1.Analysis on the difference of rice yield and the efficiency in different yield levels of rice stubble and wheat in middle and low reaches of Yangtze RiverThere are significant differences in the yield difference of rice stubble and wheat in the middle and low reaches of the Yangtze River.The yield difference of rice stubble and wheat in Jiangsu Province is mainly concentrated in Yg2(yield gap 2)which is the yield difference between the level of farmers and the level of high-yield research,while in Anhui Province and Sichuan Province it is mainly Yg3(yield gap 3),which is the yield difference between the light and temperature upper limit potential record and the high-yield research yield is large.In the investigation of yield difference and efficiency difference in two typical ecological regions of Jiangsu Province,the main experimental sites in Guannan are Ygl(yield gap 1)and Yg3,which are the yield difference between high-yield farmers’output and ordinary farmers’ output,and the yield difference between experimental output and high-yield records,respectively.The Jintan experimental site is mainly Yg3 and Yg4(yield gap 4),which are the yield difference between the experimental yield and the high yield record and the yield difference between the high yield record and the upper limit potential of light and temperature,respectively.Both regions have the highest nitrogen fertilizer productivity at the experimental yield level and the lowest nitrogen fertilizer productivity at the general farmer yield level.However,in terms of restrictive factors,low food prices,poor benefits,difficulties in selling the grain and the guidance of the national food policy have become the social and economic factors that limit the farmer’s effort towards rice and wheat cultivation.However,irrational variety selection,chemical control technology,sowing quality problems and mismatch of agricultural machinery and agronomy are the main factors affecting the yields.Climate change,waterlogging,drought and insufficient light are the main climate limiting factors that farmers believe to restrict the increase of wheat yield after rice in Jiangsu Province.2.Characteristic population differences in different yield levels of rice and wheat in Jiangsu provinceThe simulation-controlled experiment of yield difference in Jiangsu Province showed that there were significant differences in population traits among different yield levels of rice and wheat stubble.In this experiment,the hierarchical differences in panicle number and grain number per panicle were the main reasons for the yield level differences.However,in a correlation analysis between the major population traits and the yield,major population traits are significantly correlated with the ear number and grain number per ear.Among them,the most influential factors are the four indexes of tiller panicle formation rate,population photosynthetic rate,the harvest index and the leaf area canopy distribution.In terms of tiller panicle formation rate,the criteria for reaching the four yield levels(T1,T2,T3 and CK)are>47%,45%,40%and<40%,respectively.The population photosynthetic rate was>23μmol CO2 m-2 g-1,about 21μmol CO2 m-2 g-1,about 20μmol CO2 m-2 g-1,and<18 μmol CO2 m-2 g-1.The harvest index is>0.45,about 0.43,0.35～0.4 and<0.35 respectively.The distribution of upper and middle layers of LAI are>85%,>85%,<80%and<80%respectively.3.Differences of individual traits in different yield levels of rice stubble wheat in Jiangsu provinceThere were significant differences in SPAD,plant height,internode composition index,grain-leaf ratio,flag leaf net photosynthetic rate,leaf area and fluorescence parameters among different yield levels of rice and wheat stubble.The main individual traits that played a significant positive correlation to yield formation were plant height composition index,grain-leaf ratio,SPAD value and flag leaf net photosynthetic rate.Moreover,the main individual traits that have significant positive correlation with the yield also significantly affect the number of panicles and grains per panicle,eventually affecting the yield.In terms of plant height composition index,the criteria for reaching the four yield levels(T1,T2,T3 and CK)are>0.6,about 0.6,<0.6 and<0.6 respectively.The grain-leaf ratio was>0.35,0.3～0.35,<0.3,<0.3 respectively.SPAD values are about 58,about 58,about 55 and<50 respectively.The net photosynthetic rate of flag leaf is about 25 μmol CO2 m-2 g-1,23 μmol CO2 m-2g-1～25 μmol CO2 m-2 g-1,20 μmol CO2 m-2 g-1～23 μmol CO2 m-2g-1and<20 μmol CO2 m-2 g-1,respectively.