Effects Of Biochar Addition On Soil Greenhouse Gas Emission And Soil Physical And Chemical Properties In Dryland Farmland Of Loess Plateau

The soil and water loss is serious in the Loess Plateau,which leads to the obvious decrease of soil nutrient and quality.Biochar is widely used in soil improvement.Biochar applied to soil can increase crop yield and soil bioactivity in a short period of time.However,it is not clear whether biochar can reduce greenhouse gas emissions,improve soil nutrients,organic nitrogen composition and content after 5 years of soil application.Based on the long-term positioning test of dryland spring wheat field in Longzhong Loess Plateau in 2015,six levels of biochar addition were set up(CK:0t·hm^-2?BC1:10 t·hm^-2?BC2:20 t·hm^-2?BC3:30 t·hm^-2?BC4:40 t·hm^-2?BC5:50 t·hm^-2)in the dry-farming agricultural comprehensive experimental station of Gansu Agricultural University.By measuring the emission patterns and environmental factors of soil microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),enzyme activity,soil organic nitrogen components,crop yield and soil greenhouse gas(CO₂ and N₂O)in 0-5 cm,5-10 cm and 10-30 cm soil layers,and combining with variance analysis and correlation analysis,the relationship between different levels of biochar addition and soil properties as well as greenhouse gas emissions was discussed.It provides a theoretical basis for reducing greenhouse gas emissions,improving soil quality and environmental protection in dry-farming areas of Longzhong Loess Plateau.The main findings are as follows:1.The addition of biochar increases the content of soil organic matter(SOM)and total nitrogen(TN).The 0-5 cm and 5-10 cm soil layers have the highest SOM content when treated with BC4,which are significantly increased by 45.73%and 31.47%respectively compared with CK(P<0.05),there is no significant change in the SOM content of the 10-30 cm soil layer.The TN content of the soil was the highest when treated with BC5,and the TN content of 0-5 cm,5-10 cm and 10-30 cm soil layers were significantly increased by 10.94%,10.25%and 6.52%compared with CK,respectively.The content of total phosphorus(TP)in the 5-10 cm soil layer was the highest in BC2treatment,which was significantly increased by 31.56%compared with CK.The content of soil available potassium(AK)was the highest in 0-5 cm soil under BC3treatment,which was significantly increased by 25.78%compared with CK.Biochar has no significant changes in the total potassium(TK)and available phosphorus(AP)content of each soil layer.2.The addition of biochar increases the soil MBC content,and the soil MBC content is the highest when treated with BC5.In the 0-5 cm,5-10 cm and 10-30 cm soil layers,the MBC content of the soil was significantly increased by 89.89%,68.63%and139.74%(P<0.05)when treated with BC5,respectively(P<0.05);There was no significant change in MBN content.Biomass charcoal improves soil nitrate reductase(NR)activity,and BC5 treatment soil NR activity is the largest.In 0-5 cm,5-10 cm,and 10-30 cm soil layers,the NR activity of soil under BC5 treatment was significantly increased by 1027.17%,255.565%and 111.33%compared with CK,respectively;Catalase(CAT)activity under BC2 treatment Compared with CK,the 0-5 cm soil layer was significantly increased by 7.15%,and the invertase(INV)activity was significantly increased by 12.18%compared with CK in the 5-10 cm soil layer.There was no significant difference between the two in other soil layers and treatments.Biomass charcoal treatment had no significant effect on soil alkaline phosphatase(ALP)and urease(UR)activities in all soil layers.3.The addition of biochar increases the content of soil acidolytic total nitrogen(TAN),amino acid nitrogen(AAN),acidolytic ammonium nitrogen(AMN)and amino sugar nitrogen(ASN).The content of TAN,AMN and ASN in the soil of 10-30 cm soil was the highest under BC3 treatment,which increased by 107.55%,91.91%and 99.74%respectively compared with CK(P<0.05).The content of AMN was significantly reduced only under BC5 treatment.The content of AAN in the soil was the highest when treated with BC5,which increased by 81.51%,77.27%and 71.04%in 0-5 cm,5-10 cm and 10-30 cm soil layers,respectively.With the increase of the amount of biomass charcoal,the soil acid hydrolysis unknown nitrogen(UAN)content showed a decreasing trend,and the content was the lowest in the BC5 treatment,which was significantly higher than that of CK in the 0-5 cm,5-10 cm and 10-30 cm soil layers.Decrease by 89.57%,78.34%and 57.42%.Through correlation analysis,it can be known that soil TN and SOM are the main factors affecting the difference of organic nitrogen components,which have a significant positive correlation with AAN,AMN and non-acid hydrolysis nitrogen(AIN),and a significant negative correlation with UAN;MBC is the second.There was a very significant positive correlation with AAN and AIN,and a very significant negative correlation with UAN.4.BC1 and BC4 treatments can increase the cumulative emissions of soil CO₂,while BC2,BC3 and BC5 treatments can reduce the cumulative emissions of soil CO₂.Among them,the BC3 treatment has the lowest cumulative emissions of CO₂,which is significantly lower than CK by 32.32%(P<0.05).The addition of biomass charcoal can significantly reduce the cumulative emissions of N₂O,and the cumulative emissions of N₂O treated with BC3 are the lowest.The comprehensive warming potential effect of biomass carbon treatment of soil greenhouse gases CO₂ and N₂O is as follows:BC1>CK>BC4>BC5>BC2>BC3.In dry farmland,soil temperature and air temperature are extremely significantly positively correlated with greenhouse gas emission fluxes in each soil layer,and soil moisture content is only extremely significantly negatively correlated with greenhouse gas emission fluxes in the 10-30 cm soil layer.Related.To sum up,the addition of biomass carbon can affect soil nutrient content,regulate the distribution of soil organic nitrogen components,improve soil quality and reduce soil greenhouse gas emissions.When BC3 treatment,the wheat yield was the highest,and the effect of reducing greenhouse gas emission was the best.In view of economy and environment protection,30 t·hm^-2 is recommended as biomass carbon in the improvement of wheat field in Longzhong Loess Plateau.