| According to the results of question surveys on the yield levels of wheat in wheat after rice region belonging to the middle area of Jiangsu Province,there were significant wheat yield gaps between household yield and high yield levels,as well as household yield and high-yield record levels.In order to study and analyze the main reasons of yield gap and utilization efficiency gap at different levels,and explore the optimum cultivation measures for a local traditional mode to improve yield and narrow the gap,the wheat varieties Ningmai 13 and Yangmai 25,local wheat varieties,were planted in five cultivation modes:high density and fertilizer-free mode(CK),high density and nitrogen-free mode(Y0),high density and high nitrogen mode(Y1,traditional mode),medium density and medium nitrogen mode(Y2),low density and medium and high nitrogen mode(Y3).Combined with in-home survey data and meteorological data from 2016 to 2020,the main reasons for the yield gap were analyzed from social factors,biological and abiotic factors,cultivation factors,etc..The utilization efficiency gaps of heat,light and fertilizer resources among different modes were clarified.On the basis of traditional modes,the regulation effect of replacing cultivation factors on narrowing yield gap and efficiency gap was explored,and the optimized cultivation measures for reducing yield gap and increasing resource efficiencies of wheat after rice in the middle area of Jiangsu were suggested.The main results are as follows:1.According to the survey data of farmers in the middle area of Jiangsu,the main farmers in wheat production were between the ages of 51and 60with junior high school education.This group urgently needed new agricultural technologies,but their acceptance ability was low.In the past four years,the highest yield level was 8400 kg.hm-2,and the gap between the yield coming from high-yield fields and the average yield was 772—2270 kg.hm-2.Wheat planted from October 26th to November 15th with sowing quantity of 241—300 kg·hm-2 achieved high yield,and high yield can be also obtained from late-sowing wheat by increasing corresponding sowing quantity.The average nitrogen application level of farmers was 280—300 kg.hm-2,the yield of a few farmers decreased when nitrogen application rate was higher than 350 kg·hm-2.Farmers thought that social factors such as low grain price and difficulties to sell grain,cultivation factors such as agricultural machinery and agronomy mismatching and unreasonable planting density,biological factors such as aphids and powdery mildew,and abiotic factors such as low temperature and poor fertility of soil were the main limiting factors that influenced the wheat yield increase.The economic benefits obtained by different wheat planting scales were different.When the planting area was 100—300 mu,most farmers got higher benefits and higher benefits per unit area.Loss-making farmers with a plant area more than 500 mu accounted for a large proportion,while a small number of farmers had income,and the benefits of wheat planting per unit area were lower.2.There were significant differences in wheat yield among different modes.The yield of each mode in Yangzhou was higher than that in Xinghua(except for 2017—2018),and the yield among different modes followed a descendant order of Y3,Y2,Y1,Y0,and CK.Among them,the highest yield of Y3 mode was 9795.14 kg·hm-2,and the highest yield of Y2 mode was 9607.14 kg·hm-2.The average yield gap(gap I)between Y3 and Y2 was 315.21 kg·hm-2,and the average yield gap(gap Ⅱ)between Y2 and Y1 was 572.94 kg·hm-2.Although the spike number of Y1 mode was high,the grain number per spike and 1000-grain weight was low,which was the main reason for the difference with Y2.The low number of grains per spike and unstable in the number of spikes were the main reasons for the difference between Y2 and Y3.The mean gap I of spike number,grain number per spike and 1000-grain weight were 8.05×104·hm-2,-0.8 grains per spike and 1.14 g,and the mean gap Ⅱwas 25.82×104·hm-2,2.79 grains per spike and-1.19 g,respectively.The yield level of wheat fluctuated greatly in different years and regions.The variation coefficient of yield in Y1 was higher(averaging 17.58%)and that in Y3 was the smallest(12.73%).The variation coefficient of yield gaps was significantly higher than that of yield.It shows that the traditional mode Y1 was more affected by climate and the yield fluctuated greatly,while the Y3 had strong disaster resistance and good stability of yield.3.There are differences in the utilization efficiency of heat and radiation resources among these modes.The interception efficiency of light energy was the highest(91.21%)from jointing to flowering among different wheat growth stages.The variation range of photosynthetic effective radiation was 532.91—779.78 MJ·m-2.Y1 had the highest photosynthetic effective radiation at early growth stage,while Y3 had the highest at the late growth stage,followed by Y2 and Y1.Compared with Y1,the RUE and HUE of Y3 and Y2 were increased by 5.88%,13.33%and 8.82%,8.70%respectively.The interannual variation coefficient of RUE was the highest in Y2 mode,with an average of 19.32%.The variation coefficient of HUE in Y1 mode was the highest and reached to 14.34%.Path analysis showed that the utilization efficiency gap of heat and radiation had the greatest direct impact on the yield gap.Stabilizing the utilization of heat and light resources of Y1 and Y2 modes was conducive to reducing the yield gap and improving the utilization efficiency of light and heat resources.4.There are differences in nitrogen absorption and utilization efficiency among different cultivation modes.The accumulation of nitrogen at maturity was the highest,and the highest accumulation of nitrogen in Y3,Y2 and Y1 modes was 296.77 kg·hm-2,274.15 kg·hm-2 and 217.33 kg·hm-2 respectively.Path analysis showed that the gap of nitrogen accumulation at flowering stage had the greatest direct impact on the yield gap,followed by the gap of nitrogen accumulation at jointing stage.The nitrogen agronomic efficiency(NAE),nitrogen partial productivity(PFP)and nitrogen physiological efficiency(RE)were all highest in Y3 mode,while the apparent nitrogen use efficiency(PE)and nitrogen harvest index were highest in Y2 mode.The interannual variation coefficient of nitrogen use efficiency of Yl and Y3 modes was higher than that of Y2 mode.The average value of gap I of NAE,PFP,Re and PE was 0.85 kg·kg-1,-0.45 kg·kg-1,2.53%and-0.4 kg·kg-1,and the average value of gap Ⅱ was 4.11 kg·kg-1,6.22 kg·kg-1,12.09%and 4.46 kg·kg-1,respectively.Path analysis of nitrogen use efficiency difference and yield gap showed that the apparent nitrogen use efficiency gap had the greatest direct effect on yield gap,followed by nitrogen physiological efficiency,while the partial nitrogen productivity had the least effect.5.Based on the traditional mode,replacing some of the cultivation measures could narrow the yield gap and increase resource utilization efficiency.The yield under the density reducing by 20%(M-20%),25%(M-25%)and 40%(M-40%)increased compared with the local traditional mode.M-20%and M-25%C56(5:1:0:2:2)treatments had the highest yield 9896.40 kg·hm-2 and 9800.83 kg·hm-2 respectively.These optimum densities and nitrogen application rates contributed to yield by 6.41%,6.18%respectively.The utilization efficiency of heat and light fertilizer in the treatments with densities reduced by 20%—40%and nitrogen application reduced by 10%—30%was higher than that in traditional mode.M-20%,M-25%C5 and M-40%had high HUE and RUE,while M-20%N-25%C5 and M-25%N-30%C5 had high NUE.The treatment with an optimized density of 225×104.hm-2(M-25%)had a higher tiller spike rate,dry matter accumulation after anthesis,potential source and grain nitrogen accumulation at mature stage than those of the traditional mode,which was the main reasons for achieving higher yield.6.According to the experimental results of two wheat-growing seasons,the cultivation techniques with high yield and high income to narrow the yield gap between the local traditional mode and above 9000 kg·hm-2 mode in the middle area of Jiangsu were as follows:Seeding from November 1 to 10,planting density from 180×104·hm-2 to 225×104·hm-2,the applied amount of N,P2O5 and K2O are kept at 300 kg·hm-2,112.5 kg·hm-2 and 112.5 kg.hm-2,with nitrogen application ratio of 5:1:2:2 at the stages of basal,tillering,jointing and booting.The cultivation measures to achieve high yield and high nitrogen efficiency are as follows:Seeding from November 1 to 10,planting density at 225×104.hm-2,the applied amount of N,P2O5 and K2O are kept at 270 kg·hm-2,112.5 kg·hm-2 and 112.5 kg.hm-2,with nitrogen application ratio of 5:1:2:2 at the stages of basal,tillering,jointing and booting. |
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