The Effect Of Biochar On Acidic Soil Amelioration And Soil Nitrification

Soil acidification has become a widespread,severe and tough puzzle in the soil management in China.It could result in the poor soil quality,nutrient leaching and heavy metal contamination,which damage the crop production and quality.The overuse of nitrogen fertilizer in production even aggravates this process.So it is urgent to seek a suitable soil amendment to solve this problem.As a popular soil amendment,biochar has been considered as a useful material in ameliorating soil acidity,improving soil fertility,as well as providing good condition for plant growth.To get a better understanding of the effects of biochar on the acidic soil(fertilizer-induced)improvement and nitrification processes,we conducted a series of experiments.We(1)applied different concentrations of biochar in the pot experiment,and characterized soil chemical indexes to explore biochar's effects on soil physico-chemical properties;(2)analyzed nitrogen dynamics in both rhizosphere and bulk soils to discover nitrification processes with biochar additions;(3)studied the effects of biochars on the microbial diversity and community structure,as well as dominant functional microbes in the soil nitrification processes,to explain the biochar's effect on nutrient availability and plant growth,also the mechanisms involved;(4)conducted a field trial to practice biochars in the soil improvement and yield promotion.The main results ark listed as follows,which provide both theoretical reference and practice experience for future application.(1)The effects of biochar on soil chemical properties.We prepared wheat-straw-derived biochar at three concentrations(0,1%and 3%)and applied on urea-treated(0,240 and 480kg N/ha)soils.Then we conducted pot experiments to study biochar's effect on soil chemical properties and barley growth.Results showed that 3%biochar increased soil pH by 0.4-0.9-fold in the first year and 0.2-1.0-fold in the second year.Biochar also increased exchangeable base cations(Ca2+?Mg2+?K+?Na+)and total C.However,urea addition weakened the liming effect of biochar.In brief,the effect of biochar was more significant in the low-dosage(240kg N/ha)urea treated soil than the high-dosage(480kg N/ha)urea treated soil.(2)The effect of biochar on soil microbial abundance and diversity.We collected soil samples from both rhizosphere and bulk soils,and then applied the high-throughput sequencing to observe microbial responses to biochar.Results indicated that biochar had little effect on microbial diversity index,but had significant effects on microbial abundance.In the rhizosphere,Proteobacteria abundance was promoted by biochar,which is involved in nutrient cycling.The responders increased significantly at the beginning and then tended to be stable.In the bulk soils,both Proteobacteria and Actinomycetes abundances were promoted which was related with soil improvement.The responders of bulk soils increased slowly and reached a peak at the later stage.Redundancy analysis and Mantel test manifested that soil properties such as pH,dissolved organic carbon(DOC),exchangeable base cations(EBC)and available N all together influenced microbial community structure.(3)The effects of biochar on soil nitrification.Biochar promoted barley seed biomass,stem biomass and root biomass by 24-46-fold,6-20-fold and 0.7-6-fold.Besides measuring soil total N and available N(NH4+?NO3-),we applied quantitative polymerase chain reaction(qPCR)techniques to analyze variations of ammonia oxidizing bacteria(AOB)and archaea(AOA)amoA gene copies in different periods.Results showed that biochar increased the total N content,however it significantly decreased NH4+ and NO3-concentrations in the rhizosphere but it had little effect on NH4+ or NO3-in the bulk soil.Biochar promoted the abundance of ammonia-oxidizing microbes(p<0.05),among them AOB increased faster than AOA.The AOA/AOB ratio was lowest in the N1C2 treatment.However,the high-dosage urea treatment inhibited biochar's effect,especially in the rhizosphere.Biochar benefited soil N retention as well as increased N availability to plants,which favored plant growth.(4)The effect of biochar on nitrifying community structure.We selected soil nitrification related functional sequences from high-throughput sequencing data,and blast with NCBI database.Then we constructed phylogenetic tree for AOA,AOB and nitrite oxidizing bacteria(NOB).Results indicated that Nitrosospira and Nitrosomonas belonging to AOB accounting for 60-85%of the total nitrifying community at the seedling stage and 61-76%at the mature stage.During the plant growth,the dominant nitrifiers transferred from Nitrosospira to Nitrosomonas,especially in the rhizosphere.During the seedling stage,biochar lowered the Nitrosomonas abundance but highered the Nitrosospira abundance.During the mature stage,biochar inceased the NOB diversity.RDA indicated that in the rhizosphere,variations of soil properties(pH?EBC?NO3-?DOC)were significantly and positively correlated with variations of nitrifying communities(p<0.01)during the seedling stage,but not during the mature' stage.We also observed positive correlations between soil pH or EBC and the nitrifying communities in bulk soils(p<0.05).However,DOC of bulk soils had no obvious correlations with nitrifying communities.(5)The effect of biochar on soil fertility and crop growth.We applied 1%biochar on different nitrogen fertilizer(urea,nitrate potassium,ammonium sulfate)treated soils and to explore the effect of biochar on soil quality and crop growth.Field data showed that biochar had roles in ameliorating soil acidity and promoting crop yield.Among them,biochar worked best at soil improvement in nitrate fertilizer treated soils.Phospholipid fatty acid(PLFA)analysis indicated biochar addition resulted in higher microbial biomass and optimized microbial community structure such as higher Gram-negative(G-)bacteria and arbuscular mycorrhizal fungi(AMF)abundances,as well as lower ratios of G+/G-bacterial PLFAs,Saturated/Monounsaturated PLFAs and Cyclopropyl/Precursor PLFAs.Biochar modified soil environment facilitated plant root growth,the synergy effect of root and microorganisms promoted the available N concentration,which benefited crop growth.