Study On Regulations Of Nitrogen On The Utilization Of Nutrient Resources In The First And Second Crops Under The Diversified Planting Mode

Food security has always been a hot topic in the world.The multiple cropping pattern of paddy-upland rotation is an effective means to improve the multiple cropping index,ensure food security and improve the utilization rate of resources.The study carried out the same design at pot and field experiment of rapeseed-rice,wheat-rice and green vegetable-rice in 2017-2019.The experiment design was as follows:Three factors split plot design was adopted,the main area was rapeseed-rice,wheat-rice and vegetable-rice rotation,the split area was rapeseed/wheat/vegetable season,conventional nitrogen application Nc(rape,180 kg·hm^-2;wheat,150 kg·hm^-2;green vegetable,180 kg·hm-²)and reduced nitrogen application Nr(rape,150 kg·hm^-2;wheat,120 kg·hm^-2;green vegetable,150 kg·hm^-2),and split-split area was N fertilizer based on the 150 kg·hm^-2 N rate in the rice season,set up 3 operations M1～M3,basal fertilizer,tiller fertilizer,panicle fertilizer was 2:2:6,3:3:4,and 4:4:2,respectively,and 0 kg·hm^-2 was used as the control,and it was recorded as M0.The pot experiment was a ¹⁵N isotope-labeled tracer study.Through the quantitative estimation of input and output of isotope labeled nitrogen fertilizer,the accurate direction of nitrogen fertilizer in dry and wet seasons was determined.Through the regulation of nitrogen fertilizer in rice season,combined with physiological and biochemical changes such as rice morphological formation,material accumulation,nitrogen utilization,soil nutrients and carbon pool components,microbial community,enzyme activity differences,yield formation and other physiological and biochemical changes,the change law of soil physical and chemical properties and the influence of nitrogen nutrition on annual productivity were explored,and the high yield,high efficiency and environment with improving the annual nitrogen recycling efficiency as the core were established.The environmental friendly diversified rice planting technology mode aims to provide theoretical basis and practical reference for the annual high-efficiency utilization of nitrogen under the diversified planting mode.The main results are as follows:1.The results of pot experiment shown that optimized fertilization under diversified planting modes can regulate nitrogen retention and improve nitrogen utilization rate,and reduce nitrogen loss.The ¹⁵N isotope labeling found that the ¹⁵N tracer in the previous crop estimated that ¹⁵N accumulation was the largest in green vegetables,followed by rape and wheat under the rapeseed/wheat/vegetable-rice model.¹⁵N residues of the previous crop had the largest accumulation of ¹⁵N in rice plants under the nitrogen fertilizer M3 operation in the rice season,accounting for 21.35%,24.91%and 46.72%of the residual nitrogen in the previous crop under Nr in rape season and green vegetable season and Nc in wheat season,respectively.The nitrogen loss rate was highest in the rape season,followed by the green vegetable season,and the nitrogen loss rate was lower in the wheat season.The nitrogen agronomic utilization rate and partial productivity of nitrogen fertilizer in rice season were highest under M3 operation under Nc and Nr in rape season.The agronomic nitrogen use efficiency and nitrogen partial productivity of rice season were highest under M2 operation under Nc and Nr in wheat season and green vegetable season.From the perspective of annual nitrogen recovery and utilization rate,the annual nitrogen recovery and utilization rate was highest in M3 under Nc and Nr in rapeseed season,and it was highest in M2 under Nc and Nr in wheat season and green vegetable season.The results showed that the nitrogen use efficiency could be improved significantly by optimizing nitrogen application.2.The results of field experiments shown that nitrogen fertilizer regulation was an important way to achieve synergistic improvement of crop annual yield and nitrogen use efficiency under diversified planting modes.The rice yield was increased by increasing the number of effective panicles and grains per panicle in M3 treatment in rice season under the condition of Nc and Nr in rape season,and the average yield was 9410.26 kg·hm^-2 and 9545.15 kg·hm^-2,respectively.The rice yield was increased by grains per panicle and 1000-grain weight in M2 treatment in rice season under Nc and Nr in wheat season,and the two-year average yields were 9459.87 kg·hm^-2 and9193.91 kg·hm^-2,respectively.The rice yield was higher in M2 treatment by increasing the number of grains per panicle and the seed setting rate under Nc and Nr in the green vegetable season,and the two-year average yields were 9370.18 kg·hm^-2and 9244.83 kg·hm^-2,respectively.From the perspective of annual yield,reasonable nitrogen fertilizer management in the rice season can reduce crop yield losses caused by reduced nitrogen application in the previous crop.Compared with Nc,the annual nitrogen can save 30 kg·hm^-2under Nr in rape season,the annual yield of crops only decreased by 1.75%under M3 treatment in rice season,and the difference was not significantly.Compared with Nc,the annual nitrogen can save 30 kg·hm^-2under the Nr of wheat season and vegetable season,but the annual yield of crops decreased by5.42%and 14.39%under M2 treatment in rice season,and the difference was significantly.The rice root length（TRL）and root volume（TRV）were increased by optimizing nitrogen fertilizer management under the diversified planting mode,and the efficient leaf area of rice,the soluble protein content and protective enzyme activity were also increased by optimizing nitrogen fertilizer management under the diversified planting mode.The content of malondialdehyde was reduced by optimizing nitrogen fertilizer management.The growth and development of vegetative organs increase the nitrogen content of the vegetative organs,the leaf area and net photosynthetic rate at the heading stage were increase significantly,while delaying leaf senescence,thus the material production was increasing significantly by optimizing nitrogen fertilizer management.Reduced the nitrogen（Nr）applied in rape season,and M3 nitrogen management in rice season has more obvious advantages.Nitrogen dry matter production efficiency and nitrogen rice production efficiency showed an increasing trend with the increase of the ratio of nitrogen fertilizer in the rice season.The results showed that the yield and nitrogen use efficiency of rice could be improved by improving root activity,enzyme activities of nitrogen metabolism and photosynthesis.3.The results of field experiments shown that optimized nitrogen fertilizer management under diversified planting modes enhances soil nitrogen transformation intensity and improves nutrient activation capacity.Stepwise regression analysis shows that rice yield=0.279×TOC+8.46×OM+0.196×NH₄⁺-N-0.242×NO₃^--N-0.017×DOC（R²=0.87*）（TOC-total organic carbon;OM-organic matter;NH₄⁺-N-ammonium nitrogen;NO₃^--N-nitrate nitrogen;DOC-soluble organic carbon）,indicating that the rice yield is highly correlated with total soil organic carbon,organic matter,total nitrogen and available phosphorus,which was influence on the rice yield.The content of soil organic matter and ammonium nitrogen in M3 treatment was highest at the mature stage of rice,and TOC in soil under different previous crops was as follows:green vegetable（Pg）>rapeseed（Pr）>wheat（Pw）.Compared with Pr and Pw,the TOC increased by 0.34%and 6.36%under Pg,respectively,and TOC increased by 5.53%,9.39%and 13.19%compared with M2,M1 and M0 under M3treatment,respectively.Overall,TOC was higher than that of other treatments under M3 treatment in rice season under reduced nitrogen in rapeseed season.The AOA and AOB are the main undertakers of ammonia oxidation,which are closely related to soil nitrogen cycle.The results showed that AOB rather than AOA was the main undertaker in the ammonia oxidation process under the optimized nitrogen management mode.The relative abundance of Proteobacteria in AOB was the highest under the combination of Nr in rape season and M3 treatment in rice season,which indicated that the model improved the relative abundance of Proteobacteria in AOB,enhanced the intensity of soil nitrogen transformation,and enhanced the nutrient activation ability.4.The optimized nitrogen fertilizer management mode under diversified planting mode promoted the decomposition of straw and increased the nutrient release rate.The results showed that the nutrient release rate of rape straw and wheat straw was potassium>phosphorus>nitrogen.After 100 days of burying,39.68%-62.34%of nitrogen,49.37%-71.43%of phosphorus and 74.75%-80%of potassium in rape straw were released;41.69%-62.37%of nitrogen,41.69%-71.08%of phosphorus and74.86%-75%of potassium in wheat straw were released.More than 75%potassium was released from the straw after 30 days decomposition,which indicated that the optimization of nitrogen management under diversified planting mode could accelerate the nutrient release of straw.From the perspective of resource efficiency and environmental benefits,the annual crop yield was no significant decrease,the annual application amount of nitrogen was reduced,the utilization efficiency was high,the transformation intensity of soil nitrogen was increased,and the activation ability of soil nutrients was enhanced under the reduced N rate during rapeseed season and 40%as basal fertilizer,40%as tillering fertilizer,and 20%as panicle fertilizer management during the rice season.It is a green planting mode with stable yield,nitrogen saving and environmentally friendly in Sichuan Basin.