| Soil phosphorus surplus and low availability were problems faced by many farmland soils.In order to explore ways to improve soil phosphorus availability,this paper studied the effects of low molecular weight organic acids on soil phosphorus forms through Meta-analysis method,and analyzed the influencing factors that promote phosphorus availability.Based on this,taking calcareous cinnamon soil as the research object,the dynamic changes of soil available phosphorus and various forms of inorganic phosphorus were determined by adding exogenous low molecular weight organic acids.Meanwhile,through pot experiments,oxalic acid was selected to study the effect of phosphorus activation and its influence on the growth and development of pakchoi.This was to explore the effect and mechanism of low molecular weight organic acids in promoting phosphorus availability in cinnamon soil.The results showed that:（1）The Meta-analysis showed that the low molecular weight organic acids could activate the calcium phosphorus,aluminum phosphorus,iron phosphorus,occluded phosphorus and organic phosphorus in the soil,with the activation amounts of 27.06%,21.34%,15.52%,8.22% and 5.42%,respectively,and the content of available phosphorus increased by 212.6%.In calcareous soils,the activation of low molecular weight organic acids to octacalcium phosphorus and decandin phosphorus was 8.36% and 11.8%,respectively,and the content of labile dicalcium phosphorus increased by 7.90%.The effect of low molecular weight organic acids on phosphorus availability was different under different conditions.The phosphorus promotion effect was better in acidic and neutral soils with low total phosphorus content.When the addition amount was less than 90 mmol·L-1,the phosphorus stimulating effect increased with the increase of the addition amount,and the best effect occurred within 1020 days after the addition.Oxalic acid and citric acid had better effect on promoting phosphorus availability.Under the condition of oscillating culture experiment,the activation of phosphorus was easier.（2）The effect of 10 mmol·kg-1 oxalic acid on the inorganic phosphorus forms was shown as activation of decalcium phosphorus,aluminum phosphorus,iron phosphorus and occluded phosphorus,and increasing the content of dicalcium phosphorus and ocalcium phosphorus.Citric acid of 10 mmol·kg-1 could activate decalcium phosphorus,iron phosphorus and occluded phosphorus,and increase the content of ocalcium phosphorus and aluminum phosphorus.The activation amount of decalcium phosphorus and iron phosphorus by citric acid was significantly correlated with the increment of available phosphorus.The activation amount of aluminum phosphorus by citric acid was significantly correlated with the increment of available phosphorus.When oxalic acid and citric acid dosage were 10 mmol·kg-1 and 100 mmol·kg-1,respectively,the content of available phosphorus in calcareous cinnamon soil could be effectively increased,and the effect lasted for 20 days.On average,the oxalic acid of 10 mmol·kg-1 could increase the available phosphorus by 11.01 mg·kg-1 which had good practical value.（3）When the dosage of oxalic acid was 10 mmol·kg-1,with and without the application of phosphate fertilizer,the treatment with oxalic acid could significantly increase the available phosphorus level in the soil compared with the treatment with no oxalic acid,and had little relationship with the application time of oxalic acid.In the absence of phosphate fertilizer,the application of oxalic acid before sowing reduced the dry weight and phosphorus uptake of pakchoi by 12.13% and 5.47%,respectively;after 20 days of sowing,the dry weight and phosphorus uptake of pakchoi increased by 5.13% and 25.86%,respectively.Under the application of phosphate fertilizer,oxalic acid was applied 20 days after sowing,and the dry weight and phosphorus uptake of pakchoi were 64.13% and 1.25% higher than that of single application of phosphorus fertilizer,respectively. |
