Effect Of Eucalyptus Waste Biochar On Transformation Of Soil Phosphorus Form In Eucalyptus Plantation

Phosphorus is one of the most important elements for plant growth and development,but most of the phosphorus in the soil exists in the insoluble phosphate which is not easy to be absorbed and utilized by plants,so the utilization efficiency is low.Phosphorus deficiency is common in the soils of Eucalyptus plantations in China.A large amount of phosphate fertilizer has become the main measure to solve the phosphorus deficiency and meet the requirements of forest growth.However,due to the low utilization efficiency of Eucalyptus for phosphorus,most of the phosphorus is fixed by the soil to form insoluble phosphorus or flows into the water with surface runoff,resulting in a series of environmental problems,such as eutrophication.As a new type of environmental material,biochar has attracted extensive attention in soil improvement,efficient utilization of waste,carbon sequestration and emission reduction,and energy application.At present,the research on biochar and its effect on soil phosphorus mainly focuses on the study of total and available phosphorus,and there are few studies on the classification of phosphorus in biochar and the transformation of phosphorus form in soil by biochar.Based on the current reports,this study uses Eucalyptus cutting residues as raw materials to study the effects of different pyrolysis temperatures on the chemical characteristics and phosphorus form distribution of biochar.At the same time,through indoor incubation experiments,the effects of biochar addition on the transformation of soil phosphorus form in Eucalyptus plantation were studied.The main results are as follows:?1?As the pyrolysis temperature increased from 300?to 700?,the conversion rate of biochar decreased from 41.1% to 24.4%,and the pH increased from 5.9 to 10.3.The pyrolysis temperature has a great influence on the total phosphorus content and various phosphorus forms of biochar.The total phosphorus content of biochar is highest at 700 ?.When the pyrolysis temperature below 500 ?,the total phosphorus content of biochar increases with the increase of pyrolysis temperature.In the experiment of phosphorus classification,the content of H₂O-P in biochar changed irregularly,but it decreased suddenly at 600 ?.The content of Na HCO₃-Pi is higher at 500 ? and 700 ?,while the content of NaHCO₃-Po is the highest at 300 ? and shows a tendency to decrease with the increase of pyrolysis temperature.The content of HCl-P is the highest at 700 ?,followed by 500 ? and 400 ?.With the increase of pyrolysis temperature,the adsorption capacity of biochar to phosphorus is gradually enhanced.Therefore,the pyrolysis temperature has a great influence on the yield,total phosphorus content,phosphorus form content distribution and phosphorus adsorption capacity of biochar.?2?The pH value of soil increased with the increase of the proportion of biochar.The pH value of C_1.0 treatment reached the maximum in the first month,and that of C_0.5 and C_2.0 treatment reached the maximum in the second month.In the two previous months,the proportion had insignificant effect on the total phosphorus content.But in the third month,it decreased with the increase of the proportion.The content of H₂O-P changed significantly after the second month,in which the C_1.0 treatment increased significantly,and the C_2.0 treatment also increased significantly at the fifth month.The content of NaHCO₃-Pi and Na HCO₃-Po have opposite rules.The content of NaHCO₃-Po is higher than that of NaHCO₃-Pi.The content of NaOH-Pi and NaOH-Po are also opposite,and the content of NaOH-Po is also higher than that of NaOH-Pi.The content of HCl-P was higher in the control group and C_2.0 treatment in the first month,and then gradually decreased.?3?In the experiment of phosphorus adsorption and desorption,biochar restrained the adsorption of phosphorus by soil,but it improved the buffering capacity and adsorption strength of soil.Among them,the C_0.5 treatment had the best phosphorus adsorption effect and buffer capacity.