Effects Of Straw Returning And Nitrogen Fertilizer Management On Yield Of Direct Seeding Rice Under Wheat/Rape-Rice Rotation And Its Physiological Basis

The promotion of rotation mode has increased grain yield,but also produced a large number of straw.Its comprehensive utilization has always been a difficult and hot spot in production.At the same time,the popularization of direct seeding rice cultivation technology has greatly improved the labor production efficiency of rice cultivation.But there is little research on the characteristics of nitrogen uptake of direct seeding rice and the nitrogen fertilizer operation mode of straw returning to the field.Therefore,this experiment is based on the typical flood-drought rotation model（wheat-rice,rape-rice）in southwest China.From2018 to 2019,a positioning experiment was carried out in Chongzhou Experimental Base of Sichuan Agricultural University.The two-factor split zone design was adopted.The main area is wheat/rape straw returned to the field（M₁）and the straw is not returned to the field（M₀）.In the sub-area,on the basis of nitrogen application rate 150kg/hm²,there were three nitrogen fertilizer management:basal fertilizer:tillering fertilizer:flower-promoting fertilizer:flower-protecting fertilizer ratio of 10:0:0:0（N₁）,3:3:2:2（N₂）and2:2:3:3（N₃）.Respectively,and no nitrogen application was used as control（N₀）.The effects of straw returning and nitrogen fertilizer management on photosynthetic characteristics,dry matter accumulation,yield components,soil nitrogen supply and plant nitrogen uptake of direct seeding rice after wheat/rape were studied.In order to clarify the yield composition characteristics and physiological basis of direct seeding rice after wheat/rape.And to select the best straw returning and nitrogen fertilizer management mode of direct seeding rice under wheat/rape-rice rotation mode.The purpose of this study is to provide theoretical and practical support for the green and simplified cultivation of rice under flood-drought rotation.The main results are as follows:1.Under the wheat/rape-rice rotation mode,the yield of straw returning was higher than that of non-returning.And the yield was significantly increased in 2019.The advantage of increasing yield was due to the synergistic increase of the number of effective panicles and grains per panicle.The yield increase effect of continuous straw returning in the second year was 5.61%/5.99%higher than that in the first year.In 2018 and 2019,the yield of rape stubble direct seeding rice was 4.97%and 6.32%higher than that of wheat stubble direct seeding rice.The effect of continuous returning rape straw to field was better than that of wheat straw.Properly increasing the proportion of panicle fertilizer could increase the differentiation of secondary branches and spikelets.But the degeneration rate was also increased.Which was finally represented by the increase of the total number of spikelets.Properly increasing the proportion of panicle fertilizer can effectively prolong the time of grain filling.Under the two rotation patterns,the nitrogen fertilizer management mode of straw returning to the field combined with basal fertilizer:tillering fertilizer:flower promoting fertilizer:flower protection fertilizer=3:3:2:2could achieve high and stable yield of direct seeding rice.The output in two years reached 10090 kg/hm²/10693 kg/hm² and10015kg/hm²/11384kg/hm² respectively.2.Nitrogen fertilizer management had significant or very significant regulation effects on dry matter accumulation,photosynthetic characteristics and yield of wheat/rape stubble direct seeding rice at main growth stages.And straw returning significantly affected the leaf area index（（LAI））and population dry matter accumulation of rice at jointing and full heading stage.When straw was not returned to the field,the application ratio of basal fertilizer:tillering fertilizer:promoting flower fertilizer:protecting flower fertilizer was 2:2:3:3,which could effectively increase the net photosynthetic rate,SPAD value and leaf area index of flag leaves of direct seeding rice,delay leaf senescence,and maintain a high population growth rate from jointing to maturity,and the advantage of dry matter accumulation was obvious.The basic fertilizer:tillering fertilizer:promoting flower fertilizer:protecting flower fertilizer was 3:3:2:2 used as nitrogen fertilizer,the population construction of direct seeding rice with wheat/rape stubble was reasonable,the photosynthetic capacity of flag leaf was stronger at seed setting stage.Compared with wheat stubble rice,rape stubble rice had better photosynthetic capacity and population growth rate at fruiting stage,so the dry matter accumulation at mature stage was more.3.Under the two rotation patterns,nitrogen management had significant or very significant regulatory effects on nitrogen accumulation,transport and nitrogen use efficiency of wheat/rape stubble direct seeding rice.Straw returning significantly increased nitrogen accumulation of rice plants,nitrogen transport of stems,sheaths and leaves,and nitrogen use efficiency in the middle and later stages.In 2018,nitrogen agronomic use efficiency,partial nitrogen productivity and apparent nitrogen use efficiency of wheat/rape stubble direct seeding rice increased by 34.96%/28.76%、2.52%/2.61%and 31.91%/22.30%.Respectively,and increased by 9.55%/31.80%、6.75%/8.77%and 1.02%/0.56%in 2019.At the same time,the nitrogen accumulation of rape-rice rotation was higher than that of wheat stubble rice,and the nitrogen use efficiency was better.Its nitrogen partial productivity and apparent nitrogen use efficiency were 4.43%and 4.19%higher than those of wheat stubble rice in2018,and increased to 7.26%and 6.60%in 2019.The continuous return of rape straw to the field is more conducive to the improvement of nitrogen use efficiency.Under straw returned combined with base fertilizer:tillering fertilizer:flower promoting fertilizer:flower protecting fertilizer=3:3:2:2 and not to return to the field with base fertilizer:tillering fertilizer:flower promoting fertilizer:flower keeping fertilizer=2:2:3:3,which could effectively increase the nitrogen accumulation rate of direct seeding rice at all stages and promote the transfer of nitrogen from stem,sheath and leaves to the panicle at fruiting stage.The nitrogen accumulation of rice plant at mature stage had obvious advantage and higher nitrogen use efficiency.Agronomic use efficiency,partial productivity and apparent utilization rate of nitrogen fertilizer of wheat/rape stubble direct seeding rice were as high as 17.87kg/kg/17.85kg/kg,67.27kg/kg/75.90kg/kg,74.93%and 77.80%.4.Soil total nitrogen changed little in all growth stages of direct seeding rice.Especially in the second year of continuous straw returning to the field,it is more beneficial to maintain the stability of soil nitrogen.Continuous returning of straw to the field and combined application of nitrogen fertilizer（basal fertilizer:tillering fertilizer:flower-promoting fertilizer:flower-protecting fertilizer=3:3:2:2）could promote nitrogen uptake by rice plants,replenish soil nitrogen pool,and maintain soil nitrogen balance.The soil total nitrogen under rape-rice rotation was higher than that under wheat-rice model.