The Characteristics Of Biochar From Halophyte Plants And The Amelioration Effect And Its Mechanism On The Salt-affected Soil

Hetao irrigation region is one of the most important grain-production areas,however,the serious salinization greatly restricts the agricultural or even the socioeconomic development.Halophyte biomass is quite abundant in this area,and it is thus theoretical and practical significance to develop and utilize these halophyte resources,and to ameliorate the saline soils.In this study,Salsola collina Pall.,swtichgrass(Panicum virgatum)and sunflower straw(Helianthus annuus Linn.)was pyrolyzed in a fixed bed slow pyrolysis system under 300,500 and 700? for 2 hours.The products of bio-oil,syngas and biochar were collected and assayed for their compositions,contents and characteristics,and then their potential application values were evaluated.Meanwhile,different ratios(0,30,75 and 150 t ha-1)of biochar were applied into the saline soil,and the effect of biochar on the soil fertility and maize growth was measured.We finally obtained the following results:(1)Around 26-48%of biochar,26-33%of bio-oil and 26-47%of syngas was obtained after the Salsola collina Pall.,swtichgrass and sunflower straw was pyrolyzed in the fixed bed pyrolysis system.The biochar properties were closely related to the pyrolysis temperature and the feedstock.For example,carbon content,pH,electrical conductivity(EC),ash,cation exchange capacity(CEC),aromaticity and basic functional groups of biochar increased with the increasing temperature,however,water-soluble nutrients and aliphaticity decreased.The properties of the above-mentioned parameters were relatively stable at 500?.However,the pH,EC and ash content in Salsola collina Pall.biochar was the highest,then in sunflower straw biochar,the lowest in switchgrass biochar.In addition,CEC and iodione adsorption capacity of Salsola collina Pall.biochar was much higher than those in others.What's more,the carbon content was highest in switchgrass biochar,them in sunflower biochar,the lowest in Salsola collina Pall.biochar.(2)The turnover characteristic of microbial biomass carbon(SMBC),nitrogen(SMBN)and phosphorus(SMBP)was greatly influenced by the biochar application.Firstly,the turnover time of SMBC increased by 121.38-148.74%in biochar-added soils compared to that in control,and its growth rate was positively related to the biochar application rate.On the contrary,the turnover time of SMBN and SMBP respectively decreased by 9.16-31.17%and 5.56-50.24%,and the higher application rate,the smaller growth rate we obtained.The percentage of N-supplying amount from the SMBN turnover to the total N-uptake amount for maize was 40%in control,however,it decreased by 5.06-20.83%in biochar-added soils;P-supplying amount from the SMBP turnover was excessive in control and low-rate biochar-added soil,however,it decreased to 50.78-73.04%in high-rate biochar added-soil(>30 t ha-1).(3)The gene abundance and community structure of the denitrifying bacteria in the saline soil was also affected in biochar-added soils.For instance,the gene copies of nirK-,nirS-and nosZ-type denitrifying bacteria respectively increased by 57.47-69.07%,114.11-137.61%and 106.41-106.41%in higher-rate biochar-added soils(>30 t ha-1)compared with the control.Proteobacteria was the major phylum in the nirK-,nirS-and nosZ-type denitrifying bacteria.In addition,the abundance and community composition of the nirK-,nirS-and nosZ-type denitrifying bacteria was also impacted on the genus level.However,a-diversity showed that biochar addition only increased the diversity of nirK-type denitrifying bacteria,but had no significant effect on that of others.Soil pH,EC and SOC are the key environmental factors to influence the composition of nirK-and nosZ-type denitrifying bacterial communities.(4)The soil physicochemical properties,maize growth and its NPK uptake in the saline soil was significantly influenced by biochar application as well.The higher biochar application rate(>30 t ha-1)significantly reduced soil bulk density,by 2.68-22.82%,and the decrease rate was positively proportional to the biochar application rate,however,it was negatively proportional to the biochar application life.Similarly,the amount of soil macroporosity and water stable macroaggregate(>250 ?m)also enhanced in biochar-added soils.In addition,the exchangeable sodium percentage(ESP)reduced by 32.82-47.48%compared with the control,and the reduce rate was positively correlated with the amount and life of biochar application.Furthermore,the soil organic carbon,total nitrogen,available N,available P and available K respectively increased by 112.34-856.92%,9.09-197.87%,8.74-48.96%,63.49-537.93%and 14.48-894.44%compared with the control,which was positively related to the biochar application rate.What s more,soil CEC also increased with the increasing of biochar application rate and its application life.Correspondingly,biochar application also enhanced the maize above-ground dry matter and its uptake of nitrogen,phosphorus and potassium,and the increase rate was positively correlated with the biochar application rate(P<0.05).