Study On Application Of Modified Biochar To Improve Phosphorus Availability In Calcareous Soil

After biochar is applied to soil,due to the differences of ecology,environment and soil environment in different regions,the effects on soil nutrient availability,crop growth and yield are also very different.Biochar is mostly alkaline,and the application effect on calcareous soil with pH greater than 7 is not obvious.In this paper,three different types of biochar（corn straw biochar,wheat straw biochar and fruit wood biochar）were modified by three chemical modification methods（KH₂PO₄ modification,citric acid modification and HCl modification）,the isothermal adsorption law of modified biochar was studied,and three different amounts of biochar（0.5%,1%,2%）were explored through soil culture experiments,Effects of different incubation time（7,14,21,40,60 days）on soil available phosphorus content,and effects of modified biochar on wheat growth and phosphorus uptake.The main results of this paper are as follows:（1）After citric acid modification,the pH value of three kinds of biochar decreased to below 2.72.After washing,the pH value of biochar modified by different citric acid and HCl was significantly higher than that of untreated biochar.KH₂PO₄ modification treatment increased the available phosphorus content of the three biochar by 74.5%,105.2%and 3420.3%respectively.The adsorption capacity of phosphate on fruit wood biochar ranged from 500 to800 mg/kg,which was higher than that of the other two biochar.After HCl modification,the maximum adsorption capacity of corn and wheat straw biochar increased by 35.5%and 15.3%respectively,and the maximum adsorption capacity of fruit wood biochar decreased by 25.2%.（2）After the biochar of the three materials modified by KH₂PO₄ was applied to the soil,the content of available phosphorus in the soil could be significantly increased（P<0.05）,with a maximum increase of 394%.With the increase of time,the content of available phosphorus in the soil showed an increasing trend.After washing,citric acid modified corn straw biochar could increase the content of available phosphorus in soil.The three biochar modified by HCl failed to significantly increase the content of available phosphorus in soil.The three kinds of biochar modified by KH₂PO₄ significantly increased（P<0.05）the content of available phosphorus in soil at the dosage of 2.0%.There was no significant difference between the three application rates of citric acid modified and HCl modified corn straw on the content of soil available phosphorus.（3）The application of KH₂PO₄ modified biochar increased wheat biomass by22.6%～17.5%and phosphorus uptake by 15%～145%.The application of citric acid and HCl modified biochar failed to significantly increase wheat biomass and phosphorus uptake.Among the three different application rates,0.5%application rate had the best effect on wheat biomass,and 1.0%application rate had the best effect on wheat phosphorus uptake.The results showed that the pH value and available phosphorus content of biochar modified by citric acid and hydrochloric acid decreased significantly,and the pH value of biochar modified by different citric acid and hydrochloric acid increased significantly after washing;KH₂PO₄ modification significantly increased the content of available phosphorus;The saturated adsorption capacity of fruit wood biochar to phosphorus is the highest,and the adsorption capacity of corn and wheat straw biochar to phosphorus will be further enhanced by HCl modification;After KH₂PO₄ modified corn straw,wheat straw and fruit wood biochar were applied to the soil,the content of available phosphorus in the soil was significantly increased.The washed biochar treatment showed that the content of available phosphorus in the soil increased with time.KH₂PO₄ modified biochar can be used as a slow-release material of soil phosphorus;The application of KH₂PO₄ modified biochar can significantly increase the biomass and phosphorus uptake of wheat.The optimal dosage of corn straw,wheat straw and fruit wood biochar are 0.5%-1%.In conclusion,biochar application after appropriate modification can effectively improve soil pH,increase soil available phosphorus content,and play a positive role in the growth of wheat.Modified biochar can be used as a material for slow-release phosphorus in soil.The research conclusion provides a scientific basis for the rational application of modified biochar.