| Currently,straw returning,as an important agronomic application,was paid a lot of attentions worldwide.Previous studies showed that straw returning has the abilities of enriching the soil fertility,improving soil quality,reducing chemical fertilizer application level;however,straw returning has a negative effect on the crop production in the current season that also influences the promotion and application of straw returning technology.The study was carried out from 2014 to 2016 on the Experimental Farm of Key Laboratory of Crop Genetics and Physiology of Jiangsu Province in Yangzhou University.Using Yangfumai 4 as the wheat variety,the influences of full straw returning lasting for different years on soil nutrients,greenhouse effect,grain yield and quality of wheat plants were studied to explore the appropriate straw returning years for achieving high grain yield and quality.The research aimed to provide theoretical basis and technical support for the improvement of high yield and quality,efficient and low carbon wheat production under the conditions of full straw returning.The main results are as follows:1.The grain yield under the treatments of full rice straw returning lasting for 1-3 years was lower than the treatment of no straw returning,the main reason for lower yield was that full rice straw returning reduced the panicles of wheat.Compared with the treatment of no straw returning,the full rice straw returning lasting 4-7 years increased grain yield,this was because that full rice straw returning increased the number of spike and grain.The yield under the nitrogen application rate of 5:1:2:2 was higher than those under 3:1:3:3 nitrogen fertilizer and 7:1:2:0 nitrogen fertilizer on the yield of same nitrogen fertilizer with different nitrogen application rate.The grain quality was regulated by straw returning in wheat,this might due to that full rice straw returning increased the contents of grain protein and grain hardness.The wet gluten,sedimentation readings and flour extraction of grain all reduced before straw returning,however they were gradually increased with the increase of rice straw returning years.2.The contents of nitrate N(NO3-—N),ammonium N(NH4+—N),available phosphorus and available potassium dynamic changed because of straw returning and fertilizer in different periods.The nitrate N and ammonium N content in the soil decreased before wheat seeding due to the straw degradation microbial fixation of nitrogen was not conducive for the growth and development in the plant early stage.With the advancement of wheat,straw degradation comes into nitrogen release period,resulting in soil nitrate N and ammonium N content increased at middle and late stage especially heading-blooming stage which created a optimal condition for the nitrogen accumulation in the middle and late stage in wheat.The rice straw returning increased the nitrate N,ammonium N,instant phosphorus,instant potassium and organic matter content of soil.When the straw returning years increases,the concentrations of nitrate N,ammonium N,available phosphorus,available potassium and organic matter increased gradually at all levels of soil as well,which means that rice straw returning is helpful to improve soil fertility.3.The full rice straw returning increased the cumulative soil emissions of CH4 and CO2 during wheat growing season and increased with the increase of returning years,whilst reduced the cumulative emissions of N2O.Full rice straw returning increased the amount of net GWP and still increased along with the increasing of straw returning years.Although rice straw returning increased the net greenhouse gas emissions compared with no straw returning,some of the carbon(C)and N sources in the straw were converted to organic matter and nitrate nitrogen and ammonium nitrogen in the soil.Hence,the full rice straw returning has certain comprehensive emission reduction effect.The longer the returning year of the straw was,the reduction effects were better.4.The seedling growth was affected by rice straw returning as well.The weak growth of wheat seedlings and the decreased tiller number could be observed in this study.With the returning year increases,the soil nutrient supply capacity increases gradually while the adverse effects of crop residues gradually decreases.At the same time,LAI and dry matter accumulation of wheat stalks gradually increased.Dry matter accumulation after flowering represents 74.34%to 83.77%percentage of grain dry weight.There exists significant linear relationship between the dry matter accumulation after flowering and grain yields of wheat.5.The full rice straw returning helps to improve the SPAD and net photosynthetic rate of the flag leaves in wheat,also these values increases with the returning year increases.This is probably due to the straw decomposition could provide sufficient nitrogen for wheat and delay senescence with the increase of returning years of rice straw.The SPAD and net photosynthetic rate in the flag leaves under the nitrogen application ratio of 5:1:2:2 and 3:1:3:3 were higher than the nitrogen application ratio of 7:1:2:0 treatment.The results showed that it was necessary to increase the amount of fertilizer in the seedling stage to cultivate strong seedlings and rationally use the jointed booting fertilizer to delay the senescence and improve the ability of photosynthetic production and ability of grain grouting.6.The full rice straw returning increased the nitrogen and phosphorus accumulation,improved the N and P translocation amount,N and P translocation efficiency of vegetative organs and contribution efficiency to grain.The nitrogen application ratios of 5:1:2:2 and 3:1:3:3 were more favorable to the accumulation of N and P.The increase of returning years was conducive to increasing the N and P accumulation,improving the N and P translocation amount,N and P translocation efficiency of vegetative organs and contribution efficiency to grain.These indicated that the absorption,accumulation and transport of nitrogen and phosphor and grain yield were improved by continuous full rice straw returning. |
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