Influence Of Biochar Addition On Phosphorus Transformation And Bioavailability In Soils

Phosphorus is one of large amount elements for plants to grow, but most of phosphorus is existed by undissolved form in the soil. So it is difficult to be used by the plant, resulting in phosphorus as the limited factors for plant growth in many areas. Traditional remedy is applying phosphate fertilizer. But use efficiency of phosphorus is very low. Excessive use of phosphate fertilizer could cause the eutrophication of water bodies. In recent years, biochar received much attention, in carbon sequestration and soil improvement. These studies have shown that biochar could amend soil p H and CEC. In addition, biochar contains large amount of phosphorus which can be used forcrops. But most of the research mainly focused on the effect of biochar on total phosphorus and available phosphorus, little is known about the impact of biochar on the transformation of phosphorus forms in the soil. In this study, we combined chemical fractionation and 31 P nuclear magnetic resonance(NMR) method to study and the influence of feedstock(corn, wheat, peanut shells) on the transformation of phosphorus forms at different carbonization temperature. Then we incubated the sampled soil applied with biochar with and without phosphorus fertilizer for one month. And we studied the influence of biochar on the transformation of the forms of phosphorus in the soil at different times. Finally, we planted Suseda salsa to study the effect of biochar on crop yield, the uptake of phosphorus and the transformation of phosphorus between crop and soil. the main conclusions came as follows:(1) The content of total phosphorus(TP) and total inorganic phosphorus(TIP) in biochar increased at first and then decreased as the carbonization temperature rising, while total organic phosphorus(TOP) showed an increasing trend. The water extracted phosphorus(H2O-Pi) increased at first and then decreased with rising temperature. Labile inorganic phosphorus(Na HCO3-Pi) reached the highest content at 300℃ or 400℃, moderately labile inorganic phosphorus(Na OH-Pi), labile organic phosphorus(Na HCO3-Po) and secondary labile organic phosphorus(Na OH-Po) all showed a reducing trend with rising carbonization temperature.By contrast, apatite p(HCl-Pi) increased in this process. The 31 P NMR showed phosphate(Orhto-p) increased first and then decreased, pyrophosphate(Pytho-p) decreased, and organic phosphorus significantly reduced with rising carbonization temperature. The solid state nuclear magnetic results of were relatively complex. The content of organic phosphorus in different extraction methods was inconsistent,In generally, the feedstock and carbonization temperature had significant impact on the TP, TIP, TOP and their forms.(2) Biochar had a positive priming effect on the forms of phosphorus in acid soil at the 4 day. Over the incubation process, the positive priming effect of biochar on H2O-Pi, Na OH-Pi increased, and negative priming effect of biochar on Na HCO3-Pi was observed, suggesting that biochar was favorable for the formation forms of phosphorus. The priming effect of biochar on Na HCO3-Po from positive to negative indicated that biochar could promote soil microbial activity, shift Na HCO3-Po to inorganic phosphorus. The priming effect of biochar on HCl-Pi was reduced, which suggested that the addition of biochar could transfer HCl-Pi to other forms of P.(3)For alkaline soil, biochar had a negative effect on different forms of phosphorus except for Na HCO3-Pi and HCl-Pi. But with increasing incubation time, the priming effect of biochar on H2O-Pi shift from negative to positive effect. The priming effect of biochar of high temperature(400℃-600℃) on Na HCO3–Pi was more pronounced, however the priming effect of 300℃ biochar on Na HCO3-Pi changed from a positive to negative which suggested that the high temperature biochar can increase the content of Na HCO3-Pi in the soil. The negative priming effect of biochar on Na HCO3-Po was observed due to the increase the amount of Na HCO3-Po in the alkaline soil. Biochar enhanced negative priming effect on Na OH-Pi to show biochar can transfer Na OH-Pi to other forms. Biochar priming effect on Na OH-Po from negative to positive effect and positive priming effect on HCl–Pi was less noticeable.(4)In early incubation time, phosphate fertilizer mainly transformed to the inorganic phosphorus while the transformation became complex in the later incubation time. The content of soil available phosphorus decreased with increased incubation time.(5)Based on the two growth seasons of Suseda salsa, biochar significantly(P = 0.05) increased the Suseda salsa biomass, and enhanced plant phosphorus concentration. Biochar produced at low temperature(300℃) showed more beneficial for the growth of Suseda salsa and uptake of phosphorus. The effective use of p with biochar application could be maintained for at least two growth seasons. But biochar amendment combined with phosphate fertilizer, the Suseda salsa biomass change was not significant compared with control. In the first growth season, the uptake of phosphorus of Suseda salsa decreased, and this trend became better in the second growth season. The lack of synergy between biochar and phosphate may be associated with phosphorus content and proportion of biochar, which needs further research.In conclusions, from the plant growth and the phosphorus use efficiency, low temperature(300℃ and 400℃) biochar showed more advantage to increase the available phosphorus in the soil and subsequent plant biomass.