Effects Of Density And Combined Application Of Nitrogen And Phosphorus On Nutrient Absorption And Yield Of No Tillage Direct Seeding Rapeseed

No-tillage（NT）direct seeding cultivation technique is a simplified and efficient cultivation technonogy that is beneficial to expand the planting area and utilize the vast winter fallow field in rapeseed production,due to the reduction of rotary tillage（RT）procedure before sowing which reduced the labor cost and improved planting benefit and planting enthusiasm of the farmers.However,there is still a lack of systematic research on the suitable density,fertilization amount and physiological basis of NT direct seeding cultivation technique in rapeseed（NT direct seeding rapeseed）.The traditional cultivation techniques and management methods are still widely used in rapeseed production,which is hard to achieve the goal of high-and stable-yield,and fails to take advantage of NT direct seeding rapeseed.In this study,two experiments were carried out in Beibei district of Chongqing from 2019 to 2021:（1）the density experiment adopted the split plot experimental design which applied two cultivation measures,namely NT-and RT-direct seeding methods as the primary area with two planting densities of 300000 plants/hm²（D1）and 450000 plants/hm²（D2）as the secondary area;（2）the experiment of combined application of nitrogen（N）and phosphorus（Pi）fertilizer used the split plot design as well which applied three N fertilizer application rates of 0kg N/hm²（N0）,180kg N/hm²（N1）and 360kg N/hm²（N2）as the primary area with four Pi application rates of 0kg P₂O₅/hm²（P0）,45kg P₂O₅/hm²（P1）,90kg P₂O₅/hm²（P2）and 135kg P₂O₅/hm²（P3）as the secondary area.In order to provide theoretical foundation for the high-yield and high-efficiency NT direct seeding rapeseed in the upper reaches of Yangtze River,we explored the effects of density and combined application of N and Pi fertilizer on nutrient absorption and yield of NT direct seeding rapeseed,by measuring the agronomic traits,photosynthetic characteristics,dry matter accumulation,nutrient absorption,yield and quality,and lodging index.The main results are as follows:1.The effect of density on photosynthetic characteristics of NT direct seeding rapeseedOur resulte showed that the net photosynthetic rate per plant of NT direct seeding rapeseed significantly decreased in high density treatment（D2）as compared with control（D1）.In 2019-2020,the net photosynthetic rate per plant at seedling stage decreased by 13.3%,and in 2020-2021 the net photosynthetic rate per plant at seedling,budding and flowering stages decreased by 18.2%,15.6%and 12.2%respectively.However,the leaf area index of NT direct seeding rapeseed was significantly increased in density treatment（D2）.In 2020-2021,the leaf area index was significantly increased by 60.2%,15.5%and 20.7%at seeding,budding,and full-blooming stage,respectively.2.Effects of density on nutrient uptake in NT direct seeding rapeseed.Under high density condition（D2）,the root vigor of NT direct seeding rapeseed decreased significantly as compared with the low density（D1）which decreased by 53.3%and 65.0%at full-blooming and silique stages in 2020-2021 respectively.However,due to the population dominance of D2 treatment than that of D1 treatment,N and Pis accumulation of NT direct seeding rapeseed at mature stage increased remarkably by15.9%and 38.8%respectively.3.Effects of density on dry matter accumulation and yield of NT direct seeding rapeseedIn high density treatment（D2）,the dry matter accumulation of NT direct seeding rapeseed increased significantly,which were increased by 53.3%,21.8%,9.3%,14.2%and 16.6%at seeding,budding,full blooming,silique and mature stages in 2020-2021,respectively.The yield of NT direct seeding rapeseed was 2360.0kg/hm² and2220.0kg/hm² in 2019-2020 and 2020-2021 respectively,which was significantly higher than that of the D1 treatment,with an increase of 11.2%and 21.9%respectively.4.Effects of N and Pi fertilizers combined application on photosynthesis trait of NT direct seeding rapeseedOut results demonstrated that suitable N and Pi combined application could enhance the photosynthetic capacity of NT direct seeding rapeseed.The net photosynthetic rate of NT direct seeding rapeseed showed an increasing trend anlong with the increaseed N fertilizer levels.For example,compared with N0P1,the net photosynthetic rate at budding stage of N1P1 and N2P1 treatments were significantly increased by 8.0%and 11.2%,respectively.However,there was no obvious change of net photosynthetic rate at different development stages of NT direct seeding rapeseed after adding Pi fertilizer under the same N fertilizer application level.Meanwhile,along with the increasement of N fertilizer application level,the leaf area index of NT direct seeding rapeseed exhibited an increased trend as well.For instance,as compared with N0P1,the leaf area index at budding stage of N1P1 and N2P1 treatments were significantly increased by 206.3%and 690.6%,respectively.With the increased Pi fertilizer application level,the leaf area index of NT direct seeding rapeseed showed a increased and then decreased trend.For example,as compared with N1P0,the leaf area index of N1P1,N1P2 and N1P3 treatments significantly increased at budding stage by5.9%,18.2%and-6.7%,respectively.5.Effects of N and Pi fertilizers combined application on nutrient absorption in no-tillage direct seeding rapeseedWe found that suitable N and Pi fertilizers combined application could enhance the nutrient uptake capacity of NT direct seeding rapeseed.With the increasement of N fertilizer application level,the N and Pi accumulation of NT direct seeding rapeseed at mature stage both showed an increased trend.For example,as compared with N0P1,the N accumulation at mature stages of N1P1 and N2P1 treatments were significantly increased by 371.5%and 690.2%,respectively,whereas the Pi accumulation was significantly increased by 154.6%and 245.7%,respectively.Along with the increasement of Pi fertilizer application level,the N accumulation of NT direct seeding rapeseed at mature stage firstly increased and then decreased,while the Pi accumulation showed an increased trend.For example,as compared with N0P1,the N accumulations of N1P1 and N2P1 treatments at mature stage were significantly increased by 58.4%and 25.4%,respectively,whereas N1P3 treatment had no obvious change.Nevertheless,the Pi accumulations of N1P1,N1P2 and N1P3 treatments at mature stage significantly increased by 29.4%,61.2%and 66.9%than that of N1P0 treatment,respectively.6.Effects of N and Pi fertilizers combined application on dry matter accumulation and yield of NT direct seeding rapeseedOur results show that suitable N and Pi fertilizers application promoted the dry matter accumulation and yield formation of NT direct seeding rapeseed.With the increased N fertilizer application level,the total dry matter accumulation of NT direct seeding rapeseed showed an increasing trend,whereas the dry matter accumulation of NT direct seeding rapeseed firstly increased and then decreased with the increasement of Pi fertilizer application level.With the increased N fertilizer application level,the yield of NT direct seeding rapeseed also showed a rising trend.For example,the yield of N1P1（2480.0kg/hm²）and N2P1（2806.7kg/hm²）treatments significantly increased by 249.3%and 295.3%,respectively,compared with that of N0P1（710.0kg/hm²）treatment.With the increasement of Pi fertilizer application level,the population yield of NT direct seeding rapeseed firstly increased and then decreased.For example,the yields of N1P1（2480.0kg/hm²）,N1P2（2363.3/hm²）and N1P3（1990.0/hm²）treatments were significantly increased by 34.8%,28.4%and 8.1%,respectively,compared with that of N1P0（1840.4/hm²）treatment.After excluding the fertilizer cost,the fertilizer efficiency of N1P1,N2P1 and N2P2 treatments were significantly higher than that of other treatments.Under the experiment conditions in this study,the benefit of fertilization was more than 10,000 RMB/hm².By fitting the yield with the amount of N fertilizer and Pi fertilizers,the maximum yield of NT direct seeding rapeseed was 2864.7kg/hm²when the amount of N and Pi fertilizers was 321.7kg N/hm² and 73.2kg P₂O₅/hm²respectively,according to the fitting equation.However,the lodging angle,lodging index and Sclerotinia sclerotiorum index of NT direct seeding rapeseed significantly increased by increasing N fertilizer application levels,leading to the yield stability decreased.Moreover,with the increasement of N and Pi fertilizer application levels,the utilization rate of N and Pi fertilizers and the partial productivity decreased continuously,resulting in resources waste.In conclusion,N1P1 treatment not only improved the yield and economic benefit of NT direct seeding rapeseed,but also reduced the occurrence of lodging and Sclerotinia sclerotiorum,and it also took into account the green ecology and reduced the amount of fertilizer application,therefore was a better combination of N and Pi fertilizers combined application method in rapeseed production.