Effect Of Biochar Combined With Organic Acid On Transformation And Bioavailability Of Phosphate Fertilizer In Saline Soil

Salinized soil is widely distributed in China,especially in Northwest China.Affected by salinity,the utilization rate of phosphorus in saline soil is low.In this study,three kinds of activated materials(biochar,biocharcombinedwithoxalic acid,biocharcombinedwithcitric acid)were used in combination with phosphate fertilizer,and each material sets three levels,biochar(TBC1,TBC2,TBC3),biocharcombinedwith oxalic acid(TOA1?TOA2?TOA3),biocharcombinedwithcitric acid(TCA1,TCA2,TCA3),and a control(CK-only added with phosphorus fertilizer).The components of soil available phosphorus,water-soluble phosphorus,Microbial Phosphorus,inorganic phosphorus and organic phosphorus,as well as wheat yield and phosphorus uptake were determined by indoor cultivation and pot experiment.Syudied the effects of different materials combined with P fertilizer on the transformation of P in salinized soil in order to provide scientific basis for the efficient utilization of phosphorus in salinized soil.The main results and progress are as follows:1)Biochar,biochar+oxalic acid,biochar+citric acid combined with phosphorus fertilizer could significantly increase the content of available phosphorus in salinized soil,showed the trend of biochar+oxalic acid>biochar+citric acid>biochar,the content of available phosphorus increased with the amount of activated materials increased.As far as low molecular organic acids are concerned,oxalic acid has a better activation effect on soil available phosphorus than citric acid.The addition of high amount of oxalic acid(TOA3)could significantly increase water-soluble phosphorus in salinized soil.2)Different proportions of biochar,biochar+oxalic acid,biochar+citric acid combined with phosphorus fertilizer could significantly increase the microbial phosphorus content in salinized soil,showed the trend of biochar+oxalic acid=biochar+citric acid>biochar.As far as low molecular organic acids are concerned,medium amount of oxalic acid(TOA2)has the best activation effect.3)Biochar treatment,biochar+oxalic acid treatment(TOA3)and biochar+citric acid treatment could increase the total amount of organic phosphorus in salinized soil,in which the contents oflabile organic P(LOP)and medium-labile organic P(MLOP)were mainly increased,and the order of treatment was biochar>biochar+oxalic acid>biochar+citric acid;As for the proportion of each organic phosphorus component in total organic phosphorus,the proportion of labile organic P(LOP)increased significantly in all treatments,and showed as follows:biochar+citric acid>biochar+oxalic acid>biochar,while the proportion of medium-labileorganic P(MLOP)decreased significantly,the proportion of medium-stable organic P(MROP)increased to a certain extent,and the proportion of high-stable organic P(HROP)changed slightly.Stable organic phosphorus component could transform into the active component.4)Different proportions of biochar,biochar+oxalic acid,biochar+citric acid combined with phosphate fertilizer could affect the proportion of inorganic phosphorus components in soil,and the proportion of Ca₂-P,Ca₈-P and O-Pincreasedwith biochar treatment;The proportion of Ca₂-P,Ca₈-P,Al-P,Fe-P and O-P increased with oxalic acid treatment,and the proportion of medium oxalic acid(TOA2)increased the most,while the proportion of Ca₁₀-P decreased;The proportion of Ca₂-P,Ca₈-P,Al-P and O-P increased with citric acid treatment,and the proportion of medium citric acid(TCA2)increased the most,while the proportion of Ca₁₀-P and Fe-P(TCA1)decreased.The proportion of Ca₈-P,Al-P,O-P and Ca₁₀-P in total inorganic phosphorus varied in the order of biochar+oxalic acid>biochar+citric acid>biochar;Ca₂-P was biochar+citric acid>biochar+oxalic acid>biochar;Fe-P was biochar+oxalic acid>biochar>biochar+citric acid.On the whole,biochar+oxalic acid has a strong ability to activate inorganic phosphorus in salinized soil.5)Biochar,biochar+oxalic acid,biochar+citric acid combined with phosphorus fertilizer and only phosphorus fertilizer could significantly improve the yield,phosphorus uptake and phosphorus fertilizer use efficiency of wheat plants and grains,showing the rule of biochar+oxalic acid>biochar+citric acid>biochar>phosphorus fertilizer(except plant biomass).The plant biomass was biochar+oxalic acid>biochar>biochar+citric acid>phosphorus fertilizer.Oxalic acid treatment had the best effect on improving wheat yield and phosphorus availability in salinized soil,and high amount of oxalic acid(TOA3)was the best ratio.6)Correlation analysis showed that there was a significant positive correlation between available phosphorus and water-soluble phosphorus,total organic phosphorus,Ca₂-P.There was a significant positive correlation between water-soluble P and LOP,Ca₂-P.There was a significant positive correlation between Soil Microbial Phosphorus and total organic P(TOP).Wheat yield was significantly positively correlated with available phosphorus,water-soluble P,Ca₂-P,total organic P(TOP)and labile organic P(LOP).There was a significant positive correlation between P uptake by plant and grain and available P,TOP and Ca₂-P.There was a significant positive correlation between P use efficiency and available P,and between P use efficiency and total organic P(TOP)and Ca₂-P.In conclusion,the combined application of biochar+oxalic acid with phosphate fertilizer has a good effect on the activation of phosphorus in salinized soil,and the addition of activated materials can make the components with high stability of organic and inorganic phosphorus transform into the components with high activity,so as to improve the wheat yield and phosphorus availability.