| The key points of attention in rural areas are rich straw resources and unreasonable utilization of straw resources,excessive use of nitrogen fertilizer and reduction of nitrogen utilization rate.Therefore,the research on the effects of straw returning and nitrogen fertilizer application on soil physical and chemical properties,crop growth and yield under the double cropping system of rice and rape can provide theoretical basis and technical support for the sustainable development of local agricultural operations.In this experiment,Nei5You5399 and oilseed 817 were used as the test varieties of rice,and the experiments of straw returning and nitrogen application on soil physical and chemical characteristics,crop growth and yield were carried out in Changji Town,Sansui County,Guizhou Province from 2017 to 2019.In the rice season,two factors,straw returning?H?and nitrogen application?N?,were set up.The split plot design was adopted,in which the main plot was straw returning to the field?H?,and there were two ways of returning to the field,i.e.H1 and H2,respectively;the sub plot treatment was nitrogen application?n?,and four nitrogen application levels were set,0 kg·ha-1?N1?,75kg·ha-1?N2?,150 kg·ha-1?N3?and 225kg·ha-1?N4?.In rape season,rice straw was mainly removed from the field and returned to the field.The main results of this experiment are as follows:1.Effects of straw returning and nitrogen application on soil physical and chemical properties under under the double cropping system of rice and rape?1?physical characteristicsThe effect of straw returning on the soil bulk density of 0-7cm and 7-14cm was significant with the increase of straw returning years,but the effect on the total weight of 14-21cm soil was small.In 2017,the soil bulk density of straw returning was 1.5%,0%,2.0%lower than that of straw leaving the field,and 6.2%,2.2%,0.7%lower in2019,and the overall soil bulk density in 2019 was lower than that in 2017,and the soil bulk density of straw returning 0-7cm decreased by 10.4%.In 2017,the soil porosity,capillary porosity,capillary water holding capacity and soil aeration porosity of 0-7cm and 7-14cm straw returning to the field were lower than that of straw leaving the field as a whole,which was the opposite in 2019.In2019,the indicators of 0-7cm and 7-14cm of straw returned to the field increased by3.3%,2.1%,2.8%,1.9%,8.6%,2.1%,21.9%and 16.8%respectively compared with those of straw removed from the field,and the indicators in 2019 were larger than those in 2017.?2?Chemical propertiesIn 2017,the soil p H and organic matter of straw returning to the field were lower than that of straw leaving the field,which was the opposite in 2019;in 2017,the effect of straw returning to the field on soil available phosphorus was less,and in2019,the soil available phosphorus of 0-7cm and 7-14cm straw returning to the field increased by 2.8%and 4.8%compared with straw leaving the field.Overall,the soil p H,organic matter and available phosphorus content in 2019 are higher than that in2017.Straw returning reduced the accumulation of soil alkali hydrolyzed nitrogen;nitrogen application had a great influence on soil alkali hydrolyzed nitrogen.With the increase of nitrogen application,0-7cm and 7-14cm soil alkali hydrolyzed nitrogen showed a trend of first decreasing and then increasing,the level of N3 was the lowest,14-21cm had a trend of increasing.0-7cm H1N2 was significantly higher than H2N2,and 7-14cm H1N2 and H2N3 were significantly higher than H2N2 and H1N3,respectively.Straw returning not only increased the content of soil available potassium,but also had a significant effect with the increase of straw returning years.The interaction between straw treatment and nitrogen application had significant effect on the available potassium of 0-7cm and 14-21cm soil layers,but the difference was not significant between 7-14cm.Under the same nitrogen application condition,the available potassium of straw returning to the soil depth of 0-7cm and 7-14cm was significantly higher than that of straw returning;in 14-21cm,the available potassium of N1 and N3 straw returning to the soil was significantly higher than that of straw leaving the soil,and the difference between other treatments was not significant.The effect of straw returning on total nitrogen,total phosphorus and total potassium was small.With the increase of returning years,total nitrogen and total phosphorus decreased,but total potassium was the opposite.As a whole,with the increase of soil depth,except for soil p H,other chemical characteristics index have a downward trend.2.Effects of straw returning and nitrogen application on Rice Yield and its composition under the double cropping system of rice and rapeStraw returning can increase the yield of rice,with the increase of returning years,the effect is significant.In 2019,the yield of straw returned to the field increased by660kg·ha-1compared with that of straw removed from the field,with an increase of6.5%.There was significant difference between the treatments.Compared with 2018,H1 and H2 in 2019 increased by 1337.21kg·ha-1and 1977.05kg·ha-1respectively,with an increase of 15.0%and 22.2%.With the increase of nitrogen application,the rice yield increased first and then decreased.The highest yield was found at N3 level,which was 9636.34kg·ha-1and 11324.00kg·ha-1in 2018 and 2019,respectively.Straw returning and nitrogen application can increase rice yield,and the yield of H2N3combination is the highest,among which the yield in 2019 reached 11704.00 kg hm-2,which is 6.9%and 33.9%higher than that in h1n3 and H1N1,respectively,with a larger increase than that in 2018.From the perspective of yield composition,in 2018,the total grains and effective panicles per ear of straw returned to the field were higher than that of straw removed from the field,and the 1000 grain weight and seed setting rate were the opposite,in which the total grains and seed setting rate per ear were significantly different;in2019,except for the total grains per ear,other components of straw returned to the field were higher than that of straw removed from the field,and the 1000 grain weight was significantly different.With the increase of nitrogen application,the number of effective panicles and total grains per panicle showed an increasing trend,while the1000 grain weight was the opposite,and the change of seed setting rate was irregular.The interaction between straw returning and nitrogen fertilizer application has different effects on yield components,and has significant differences on the total grain number per panicle,seed setting rate in 2018 and 1000 grain weight and effective panicle in 2019.In 2018,the total grain number per panicle of straw returning is significantly higher than that of straw leaving the field at the same application level of N3 and N4,and the N2 level is the opposite;in the same application level of N1,the seed setting rate of straw returning is significantly higher than that of straw leaving the field In the same level of N1 application,the 1000 grain weight of straw returning to the field was significantly higher than that of straw leaving the field,and the levels of N2 and N3 were opposite.3.Effect of straw returning and nitrogen application on dry matter production and nutrient accumulation of rice under the double cropping system of rice and rapeThe effect of straw returning to the field on the tiller dynamics of rice was small,and the tiller dynamics was mainly affected by the application of nitrogen fertilizer.The number of tillers increased fastest in 9-23 days after transplanting,reached the peak in 37-43 days after transplanting,and tended to be stable in 72 days after transplanting.With the increase of nitrogen application,the plant height and tiller number of rice increased.The effect of straw returning to the field on plant height and tiller number is small,it has inhibition effect on the early stage of plant height and promotion effect on the later stage.With the increase of returning years,each critical period is higher than straw leaving the field,and the difference is significant in some periods;straw returning to the field can improve the number of tiller.At jointing stage,straw returning to the field to some extent inhibited the growth of rice,thus reducing the leaf area index;with the increase of returning years,the leaf area index at heading stage and booting stage increased.The leaf area index increased with the increase of nitrogen application.In 2018,the dry matter accumulation of straw returning to the field at jointing and heading stage was lower than that of straw leaving the field,which had little effect on booting stage,and straw returning to the field at maturity stage was higher than that of straw leaving the field;in 2019,the dry matter accumulation of straw returning to the field at each key growth stage was higher than that of straw leaving the field.With the increase of nitrogen application,the dry matter accumulation in each critical growth period increased.In 2018,the accumulation of dry matter was the largest under H2N3 treatment,and in 2019,it was the largest under H2N4 treatment,indicating that straw returning can also promote the utilization of nitrogen fertilizer.The dry matter accumulation in the stage of transplanting and jointing was lower than that in the stage of leaving the field,while the dry matter accumulation and total biomass in the stage of heading and ripening were opposite.The dry matter accumulation in the stage of jointing and heading was related to the years of returning to the field.With the increase of nitrogen application,the dry matter accumulation and total biomass of each growth stage increased.In 2018,straw returning can inhibit the dry matter output rate of rice stem and sheath,dry matter conversion rate and dry matter output rate,and in 2019,straw returning can promote the field,which shows that the effect of straw returning is better with the increase of returning years.Straw returning can promote the apparent output of dry matter.In 2018,straw returning can promote the proportion after ear,but in 2019,it is the opposite.The effect of Nitrogen Application on the dry matter transfer is great,but not regular.In the aspect of nutrient accumulation,straw returning to the field inhibited the absorption of P and K in the jointing stage and heading stage,and the absorption of N in the whole period.At the mature stage,the absorption of N,P and K by organs varied with the years of returning to the field,but promoted the absorption of P and K by rice as a whole.With the increase of nitrogen application,the nutrient absorption of each organ in each period of rice showed an increasing trend.4.Effects of straw returning and nitrogen application on PhotosyntheticCharacteristics and fluorescence parameters of rice leaves under the double cropping system of rice and rapeStraw returning can increase the SPAD value of rice,but the difference is not significant;the SPAD value increases with the increase of nitrogen application;the SPAD value increases first and then decreases with the growth of rice.Straw returning reduced the photosynthetic nitrogen use efficiency and water use efficiency at jointing and heading stage,but promoted the photosynthetic nitrogen use efficiency at heading stage.The water use efficiency at heading stage was affected by the years of returning to the field;nitrogen application and its interaction with straw returning had a greater impact on photosynthetic nitrogen use efficiency and water use efficiency.In the jointing stage of 2018,the net photosynthetic rate?Pn?of straw was significantly higher than that of straw returning to the field,with an increase of 3.7%;in the heading stage,the transpiration rate?Tr?and net photosynthetic rate?Pn?of straw returning to the field were significantly higher than that of straw leaving the field,with an increase of 6.7%and 1.6%respectively;with the increase of nitrogen application,PN and TR of rice in the whole period showed an increasing trend.In 2018,straw returning and its interaction with nitrogen fertilizer had little effect on the fluorescence parameters at the filling stage;with the increase of nitrogen application,the maximum photochemical efficiency?Fv/FM?and the photosynthetic nitrogen use efficiency at the later growth stage tended to decrease;the photochemical quenching coefficient?QP?,the quantum yield?Y?NPQ??and non photochemical quenching?NPQ?at PS?increased first and then decreased Potential:the actual quantum yield??PSII?and the apparent quantum transfer efficiency?ETR?of PS?vary irregularly under the condition of light adaptation.5.Effect of straw returning and nitrogen application on nitrogen use efficiency under the double cropping system of rice and rapeThe effects of straw treatment on nitrogen utilization were affected by the environmental factors and the years of straw returning.With the increase of nitrogen application,the partial productivity,physiological utilization rate and dry matter production efficiency of nitrogen decreased;the agronomic utilization rate,absorption utilization rate,grain production efficiency and harvest index of nitrogen increased first and then decreased;the effect on the nitrogen demand of 100 kg grain was irregular.6.The effect of straw returning and nitrogen application on the growth characteristics of rape under the double cropping system of rice and rapeIn 2018,the leaf area index of straw returning to the field decreased by 25%,5.1%and 1.2%respectively compared with that of straw leaving the field at the bud and early flowering stage,and the leaf area index of straw returning to the field increased by 8%and 4%respectively compared with that of straw leaving the field in2019;the dry matter accumulation of straw returning to the field decreased by 15.3%,12.3%,5.5%and 11.7%respectively compared with that of straw leaving the field in2018,and the rape in 2019,the dry matter accumulation of straw returning to the field increased by 15.5%,1.4%and 14.4%respectively compared with that of straw leaving the field.The change rule of nutrient accumulation and dry matter accumulation of straw returning to the field was basically the same for rape in each period.Straw returning to the field also reduced the number of pods per plant,but increased the 1000 grain weight and the number of pods per pod.This shows that straw returning has a great impact on the growth of rape in the early stage.With the time of returning to the field,the impact of straw returning on the growth of rape is gradually reduced,and the yield of rape is reduced.In the second year,straw returning has a positive correlation with the growth of rape.The results showed that the application of nitrogen fertilizer to the previous crop had a great influence on the growth of rape.Under the level of N3,the indicators of rape in bud and moss stage,initial and final flowering stage were better than those of other nitrogen application levels,but the indicators of maturity stage were slightly reduced,which may be caused by environmental factors such as climate. |
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