| In recent years,more and more attention has been paid to the research of biochar.Previous studies have been mostly focused on the effects of biochar application affecting yield of single crop,physical and chemical properties of soil and greenhouse gas emission.A long-term located field experiment was established from 2011.To make a comprehensive assement for crop respond,soil fertility change,greenhouse gas emission,carbon sequestration reduction and environmental economic benefits in the wheat/maize rotated system in fluvio-aquatic soil of north China.In the study,4 treatments waer set up expressed as BC0,BC2.25,BC6.75 and BC11.25,which represented 0,2.25,6.75 and 11.25 t ha-1 biochar added to the soil,respectively.The yield of wheat,maize,physical and chemical properties of soil,nitrous oxide emission and soil carbon sequestration was observed from 2011 to 2015.On the foundation,the individual growth index of wheat,dry matter accumulation and nitrogen absorption was studied supplemently from 2015 to 2017.And the net global greenhouse effect potential and environmental economic benefifs were also evaluated in the system so as to investigate the application potential and feasibility of straw biochar in fluvio-aquatic soil of north China plain.This paper showed the results of the late study from 2015 to 2017.The results showed that the total grain yield and total biomass over 4 seasons under BC2.25 treatment increased by 9.6% and 7.9% than BC0,respectively.BC6.75 treatment increased total grain yield,total straw yield and total biomass by 7.8%,15.3% and 12.1%,respectively.BC11.25 treatment increased total grain yield and total biomass both by 7.9% compared with BC0.Additionally,BC2.25 treatment increased harvest index by 4.8% and 1.6% in 2015/2016 wheat season and 2016 maize season.BC6.75 treatment increased harvest index of maize by 1.8% in 2016.The analysis of 2 factors between the year and the treatment showed that biochar increased the grain yield of wheat due to the increase of the number of spike;and the year significantly affected the yield components of maize.Furthermore,there were the similar effects of biochar between the increase of wheat yield and the promotion of wheat growth.Biochar treatments significantly increased the value of LAI and SPAD and amount of population in 2015/2016 and 2016/2017 that resulted in enhancing wheat photosynthesis at the overwinering stage,jointing stage and heading stage.Compared with BC0,BC2.25 increased the nitrogen accumulation in straw of wheat by 33.1%.And BC6.75 increased the nitrogen accumulation in straw of wheat 3.9%-73.8% while that of plant 10.2%-16.3%.BC6.75 also increased nitrogen accumulation in grain of maize by 12.6%.BC11.25 increased nitrogen accumulation in grain of maize by 9.3%,in straw of wheat by 69.7% and nitrogen accumulation in grain of maize by 9.3%,in straw of wheat by 69.7% and of wheat plant 19.5%.Moreover,the nitrogen partial productivity and nitrogen harvest index increased by 4.5%-24.8% and 2.5%-10.6% under 3 biochar treatments,respectively,compared with the BC0.Straw biochar continously improved soil fertility,soil structure and preserved moisture and fertility.Compared with BC0,BC6.75 and BC11.25 decreased soil bulk density by 8.1%-23.7%.3 biochar treatments increased soil total porosity,soil moisture content,and soil water holding capacity and saturated water conductivity by 5.8%-33.1%,10.5%-47.2%,27.1%-405.3% and 35.3%-405.3%,respectively.At the same time,compared with BC0,BC2.25 treatment increased ammonium nitrogen content by 14.3%,BC6.75 and BC11.25 increased nitrate notrogen content and ammonium nitrogen content 26.0%-42.2%.Additionally,BC6.75 and BC11.25 increased total nitrogen content in topsoil by 22.3%-25.4% and 30.5%-43.3%,respectively,compared with no biochar.Straw biochar sufficiently enhanced soil carbon pool and reduced nitrous oxide emission.Compared with BC0,BC6.75 treatment enhanced soil organic carbon content by 169.1%-228.5%,and BC11.25 enhanced it 176.1%-267.6%.BC2.25,BC6.75 and BC11.25 treatment biochar treatments decreased the total nitrous oxide emission by 16.5%,32.5% and 33.9%,respectively,total yield-scaled nitrous oxide emission 23.9%,37.4% and 38.5%,N2 O emission intensity by 23.9%,37.4% and 38.5%,and net greenhouse warming potential 233.4%,683.0% and 1118.0% over 4 crop seasons,respectively.Compared with no biochar treatment,the yield gains under 3 biochar treatments increased 10.5%,8.2% and 7.8% when the wheat price is 2320 CNY t-1 and maize price is 1650 CNY t-1 at current market.The biochar costs was 1200 CNY t-1,the amount of 3 treatments was 9,27 and 45 t ha-1 over 4 crop seasons,respectively.The biochar costs would increase 10.8×103 CNY ha-1 at the yield gains with 67.59×103 CNY ha-1.However,there were no significant differences among 3 biochar treatments for the yield gains,but the biochar costs would increase 3 or 5 times for BC6.75 and BC11.25.BC2.25,BC6.75 and BC11.25 reduced the net environmental economic benefits by 7.4%,50.1% and 90.5%,respectively.In conclusion,long-term biochar application could promote wheat growth and smally increase grain yield and biomass.Biochar increased grain yield by increasing number of spike.And at the same time,biochar promoted wheat photosynthesis through the increse of LAI and SPAD value.BC6.75 and BC11.25 sufficiently reduced soil bulk density,and also increased water holding capacity,porosity and saturated hydraulic conductivity,and increased total nitrogen content and mineral nitrogen content.Most notably,biochar application enhanced soil carbon pool and reduced N2 O emission,and also significantly decreased N2 O seasonal accumulation emisssion,N2 O seasonal yield-scale emission and greenhouse warming potential.However,biochar might decrease the net environmental economic benefits due to high cost of biochar made from straw in the wheat/maize rorated system at present. |
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