Effects Of Biochar Additions On Soil Phosphorus Storage And Rice Phosphorus Utilization In Acid Paddy Field

Subtropical red paddy soil has strong specific adsorption and fixation of phosphorus,and the utilization of phosphorus in the season is low.The application of biochar in farmland has been regarded as a new way to activate soil accumulated phosphorus and increase the utilization rate of phosphorus fertilizer in the season.However,the potential of biochar in acid red soil rice cultivation system to improve soil phosphorus availability and promote crop phosphorus utilization remains to be further studied.This study took the southern acidic rice fields as the object,and carried out a 5-year field location experiment using a single-factor randomized block design to explore the one-time addition of different levels of biochar（0 t/ha,20 t/ha,40 t/ha,60 t/ha,20 t/ha,40 t/ha,60 t/ha）./ha,80 t/ha and 100 t/ha)long-term effects on soil phosphorus pool and rice phosphorus absorption and utilization;Based on the results of the field experiment,three biochar levels（60 t/ha,80 t/ha,100 t/ha）with better effects on the soil phosphorus pool and rice phosphorus absorption and utilization were selected.A pot experiment of combined application of biochar and fertilizer（30%reduction,15%reduction,normal fertilization）,To evaluate the regulation and control effect of biochar on the soil phosphorus pool of acid paddy fields and rice phosphorus absorption and utilization under the condition of reduced fertilizer application,and provide a scientific basis for improving the availability of phosphorus in acid paddy fields and increasing the efficiency of phosphorus fertilizer use.Results showed that:（1）The application of biochar in acidic paddy fields significantly improved the soil phosphorus supply,and the total phosphorus and available phosphorus content in the soil showed an increasing trend with the increase of the amount of biochar added.（2）The amount of biochar applied at a time of60～100 t/ha and above can significantly increase the different active organic phosphorus（activity,medium activity,medium stability and high stability organic phosphorus）and various components of inorganic phosphorus(Ca₂-P、Ca₈-P、Al-P、Fe-P、O-P and Ca₁₀-P)content,and the effect can last for 5 years.（3）Biochar significantly increased the accumulation of phosphorus in rice grains,and the phosphorus in rice grains treated with biochar was still significantly higher than the control after 5 years of application.（4）Correlation analysis showed that soil p H was significantly positively correlated with the contents of Ca₈-P,O-P and organophosphorus with high stability,while the contents of total phosphorus and available phosphorus were significantly positively correlated with the contents of Ca₂-P,Ca₈-P,Al-P,Fe-P and organophosphorus components.Phosphorus accumulation in rice grains was significantly positively correlated with soil Ca₈-P,Al-P,O-P and high stability organophosphorus contents.（5）The pot experiment showed that compared with the control without adding biochar in normal fertilization,when the application amount of biochar reached 60-100 t/ha,the fertilizer reduced by30%had no significant effect on the contents of total phosphorus and available phosphorus in soil.Biochar combined with fertilizer reduction could significantly improve the contents of soil active organophosphorus,medium stable organophosphorus,Ca₈-P,Al-P,Fe-P,O-P,Ca₁₀-P,and phosphorus accumulation and phosphorus fertilizer utilization rate in different parts of rice were also significantly increased or maintained stable.In conclusion,the addition of biochar is beneficial to accelerate the transformation of phosphorus form in acidic paddy soil,improve the availability of soil phosphorus,promote the absorption of phosphorus in rice,and increase the utilization of phosphorus fertilizer.When the amount of biochar added reaches 60-80t/ha,reducing the fertilizer application by 30%can still ensure the phosphorus supply of the soil to the rice and improve the utilization efficiency of phosphorus fertilizer.