| Purple soil is an important cultivated land resource in China.Its soil organic matter content is low,nitrogen is scarce,soil particles are coarse,and water retention and fertilizer retention performance is poor.Biochar has great potential in improving soil physical and chemical properties and reducing greenhouse gas emissions.The effect of carbon sequestration is different due to differences in soil properties and biochar characteristics,and the impact on soil carbon pool stability is still controversial.Therefore,this paper selects two types of purple soil(acid purple soil,calcareous purple soil),three kinds of biochar materials(corn straw biochar JB,eupatorium adenophorum biochar ZB,egg shell biochar EB),the indoor culture experiment was carried out,and the effects of biochar on the organic carbon mineralization of purple soil,the structural characteristics of soil humus components and the structural characteristics of the stable black carbon components were investigated.The main findings are as follows:(1)Different sources of biomass have different physical and chemical properties of biochar materials.The specific surface area of E.adenophorum and corn stalk biochar was1.6 times and 5.16 times that of EB,respectively.The total pore volume was 48.06 times and 163.03 times of EB,respectively.The yield of EB biochar was significantly higher than that of JB and ZB.The H and C contents of JB and ZB are 3.56-5.4 times and4.49-5.2 times of EB,respectively,but the steady-state carbon ratio is higher than EB,which is 1.57 times and 1.43 times of JB and ZB,respectively.The JB cation exchange capacity is the largest,which is 1.33 times and 2.84 times of ZB and EB,respectively.(2)The application of biochar has an increasing effect on the total organic carbon content of the soil,and its growth rate decreases with the prolongation of the cultivation time.In the 0-90 days of culture,JB and ZB can increase the total organic carbon of acid purple soil by 1.13-1.34 times and 1.06-1.27 times compared with CK,which can increase the total organic carbon of calcareous purple soil by 1.72-2.05 times and 1.61-1.92 times.Both reached significant levels,while EB had no significant effect on the improvement of organic carbon in purple soil.From the perspective of soil organic carbon mineralization,the organic carbon mineralization rate of purple soil decreased with the application of biochar,and it decreased sharply in the early stage of culture(1-3d).In acid purple soil,biochar treatment accelerated soil.Organic carbon mineralization,the breathing intensity is large,the excitation effect is positive,which is not conducive to the fixation of carbon,while in the calcareous purple soil,it shows a negative excitation effect,which is conducive to carbon retention.In the middle of culture(5-15d),the trend of mineralization accelerated,and the soil excitation effect was positive.In the later stage of culture(30-90d),the soil organic carbon mineralization rate decreased and stabilized,and the respiratory intensity was gentle,with positive excitation effect.(3)Biochar application has an increasing effect on soil humus carbon content,and its growth rate increases first and then decreases with the prolongation of culture time.In the 0-90 days of culture,JB can increase the carbon content of acid purple soil humic carbon,fulvic acid,humic acid and humin component by 1.10 to 1.38 times,0.77-1.19 times,0.94-1.79 times,and 1.34-1.59,respectively.Compared with CK,ZB can increase the carbon content of acid purple soil humus carbon,fulvic acid,humic acid and humin component by 0.85-1.09 times,0.57-0.86 times,0.53-0.57 times and 1.07-1.36 times,respectively.The effect of JB and ZB treatment on the carbon content of the humus component of calcareous purple soil is greater.Compared with CK,EB also has an effect on soil humus content,but it does not reach a significant level.(4)As the culture time prolonged,the soil HA/(FA+HA)ratio(PQ)showed a trend of decreasing first and then increasing.At the end of the culture,the PQ value was improved compared with the initial culture.The HA tone coefficient of the biochar treatment is Rp type.The application of JB and ZB can increase the hue coefficient of humic acid,and the application of EB reduces the hue coefficient of humic acid.This indicates that JB and ZB simplify the composition of humic acid,which is more conducive to the accumulation of humic acid and the improvement of soil humus quality,while EB complicates the molecular structure of humic acid in soil.(5)Biochar materials were coated with a 0.45 micron filter to evaluate the effect of biochar on the stability of soil black carbon.Three kinds of biochar were embedded in the soil with a filter membrane.The black carbon content of the soil increased with the prolongation of the culture time,and then decreased first and then increased.The increase in black carbon increased slowly as the number of culture days increased.After 90 days of culture,the black carbon content of JB,ZB and EB in acid purple soil increased by 25.56%,21.30% and 8.92%,respectively,and increased by 22.56%,21.38% and 11.48% in calcareous purple soil.Both reached a significant level.In general,the application of biochar can increase the total organic carbon content of the soil,but it has a positive stimulating effect in the acid purple soil,which shows that therespiration intensity becomes stronger,the soil mineralization rate is higher than the control,and the excitation effect PE value is positive.Not conducive to the fixation of soil carbon pool.Biochar applied to calcareous purple soil inhibited soil respiration intensity and soil mineralization rate lower than the control in the early stage of culture(1-5d),which produced a negative stimulating effect,which was conducive to the fixation of carbon pool,but in the middle and late stages of culture(7-90d)Soil respiration is strengthened,soil mineralization rate is higher than that of the control,and the positive excitation effect is dominant,which is not conducive to the fixation of soil organic carbon.Biochar application can increase the carbon content of soil humic components.The humus is more stable,showing an increase in the proportion of humic acid,increasing the degree of humification,increasing the hue coefficient,and simplifying the humus structure,which is more conducive to the renewal and activation of humus.The biochar was wrapped in the soil with the filter membrane.The black carbon content of the soil decreased first and then increased with the prolongation of the culture time.The increase of black carbon increased,which was beneficial to the accumulation of organic carbon in the soil and the improvement of purple soil fertility.The carbon sequestration capacity has a promoting effect,but different types of biochar have different growth effects,and there are some differences in the black carbon increase in different types of purple soil. |
