Effects Of Interaction Of Planting Density And Nitrogen Fertilizer On Yield And Quality Of Late-sown Wheat Following Rice

Southern rice-wheat double cropping area is an important grain producing area in China,but with the transformation of production mode and the promotion of late-maturing Japonica rice varieties,the connection between rice and wheat stubble is tense,especially the late sowing of wheat has become a key factor restricting the balanced increase of annual yield of rice and wheat.Under the condition of late sowing,the individual development of wheat was weak,the population quality was poor,and the yield components were inconsistent.In order to solve this problem,the amount of nitrogen fertilizer and planting density should be increased in production.It aggravates the contradiction between groups and individuals,resulting in the reduction of nitrogen fertilizer utilization rate,the increase of production cost and environmental risk.Therefore,it is of great significance to define the critical period of late sowing under different yield levels,and to set up suitable planting density and nitrogen fertilizer management methods for building reasonable population and achieving high yield and high efficiency synergy.Field experiments were conducted in Donghai County,Suining County and Guannan County of Jiangsu Province from 2016 to 2018.Different sowing dates(S1-S5),densities(D225,D375,D525)and nitrogen application rates(N180,N225,N270)were set to study the effects of planting density and nitrogen fertilizer interaction on yield,quality and nitrogen use of late-sowing wheat after rice stubble.Based on the relationship between yield,population growth,nitrogen uptake and utilization of Rice-stubble wheat and accumulated temperature before winter,the latest sowing date and population characteristics of high yield and high efficiency of wheat were quantified.The technical way to realize high yield of late sown of wheat following rice was put forward.The main results are as follows:1.The effects of planting density and nitrogen application rate on Yield and quality of late-sown wheat in rice stubble were studied.The number of spikes,grains per spike,1000-grain weight and yield of wheat decreased significantly when sowing date was delayed.Increasing planting density increased the number of ears and yield of wheat,but decreased the number of grains per ear and 1000-grain weight.Nitrogen fertilizer increased the number of spikes and grains per spike of wheat,which increased the yield,but decreased the 1000-grain weight.The effects of planting density and nitrogen application rate on yield were different under different sowing dates.The yield of all the dense-fertilizer combination treatments of S2 and later sowing date was lower than 9000 kg hm-2.The yield of all the dense-fertilizer combination treatments of S4 and later sowing date was lower than 7500 kg hm-2.S5 sowing date yield is difficult to reach 6000 kg hm-2.The results showed that wheat yield was closely related to sowing date,and the latest sowing date of different yield levels was different.Regulation effect of density and nitrogen fertilizer was lower than sowing date.The protein and gluten contents of wheat in late sowing of rice stubble increased with the delay of sowing date,decreased with the increase of planting density and increased with the increase of nitrogen application.Starch content showed an opposite trend.Analysis of the relationship between yield and quality shows that yield increased,protein and wet gluten content decreased,starch content increased,and yield increased within a certain range did not affect wheat quality.In a certain range of sowing date,proper increase of planting density and nitrogen application rate is conducive to coordinate the yield and quality of late-sown wheat following rice.2.The effects of planting density and nitrogen application rate on population quality of late-sown wheat in rice stubble were clarified.There was a significant positive correlation between wheat yield and dry matter accumulation,leaf area index and tiller number at jointing stage.The yield of wheat,dry matter accumulation,leaf area index and tiller number at jointing stage were positively correlated with accumulated temperature before winter.The delayed sowing date reduced the accumulated temperature before winter,resulting in a significant decrease in dry matter accumulation,leaf area index,tiller number at jointing stage and yield.Under late sowing conditions,increasing planting density and nitrogen application significantly increased dry matter accumulation,leaf area index and tiller number at jointing stage,and alleviated the reduction of yield.Under the same sowing date,under the condition of high density and high nitrogen,the amount of dry matter transported before flowering decreased and the amount of dry matter accumulated after flowering increased slowly,which made it difficult to further increase yield.In order to continue to increase yield,we need to adjust the sowing date.Regression analysis showed that in order to reach the yield of 7500 kg hm-2 under late sowing conditions,it was necessary to sow before 9 November so that the accumulated temperature before winter was not less than 299.74℃·d.The accumulation of dry matter before jointing,from jointing to flowering,after flowering and during the whole growth period should be above 3630,9686,5648 and 18964 kg hm-2,respectively.The number of stems and tillers at jointing stage should reach 1273 X 104 hm-2 and LAI at flowering stage should reach 5.40.3.The effects of planting density and nitrogen application rate on nitrogen uptake and utilization of late-sown wheat after rice stubble were studied.When sowing date was delayed,nitrogen accumulation,pre-anthesis nitrogen transport,nitrogen uptake efficiency,nitrogen agronomic efficiency and nitrogen harvest index decreased.Increasing planting density and nitrogen fertilizer in a certain range increased nitrogen accumulation,pre-anthesis nitrogen transport,agricultural efficiency and absorption efficiency of nitrogen fertilizer,but decreased nitrogen harvest index.When the planting density was higher than 375×104 hm-2,the density continued to increase,the accumulation of nitrogen increased slowly,the pre-anthesis nitrogen translocation decreased,the proportion of nitrogen distribution in leaves decreased,the soluble protein content,nitrate reductase(NR),glutamine synthetase(GS)activity of flag leaves decreased significantly,and the agronomic efficiency and absorption efficiency of nitrogen fertilizer increased slowly.When the nitrogen application rate was higher than 225 kg hm-2,the nitrogen transport rate decreased and the nitrogen accumulation increased slowly before anthesis.Because the increase of nitrogen application rate is not synchronized with the increase of nitrogen accumulation and yield of wheat,the absorption efficiency and agricultural efficiency of nitrogen fertilizer decrease.Analysis of the relationship between yield and N fertilizer uptake and utilization efficiency showed that there was a positive correlation between yield and N fertilizer uptake and utilization efficiency in a certain range.Increasing density and suitable nitrogen is beneficial to the simultaneous improvement of yield and nitrogen uptake and utilization efficiency of late-sown wheat following rice.In conclusion,delayed sowing date reduced wheat yield and nitrogen uptake and utilization efficiency,but did not deteriorate wheat quality.Increasing planting density and nitrogen fertilizer can increase yield,and the effect of sowing date on yield is greater than planting density and nitrogen fertilizer.There are differences in the latest sowing date of different yield levels.In order to reach a certain yield level in production,it is necessary to sow before the corresponding critical period of late sowing and adopt reasonable regulation of density and fertilizer,so as to construct a reasonable population and eventually coordinate the yield,quality and efficient use of fertilizer of wheat.