Abstract: To meet the high-throughput detection demand for available phosphorus in neutral and alkaline soils,a combined detection system integrating ultrasonic extraction,centrifugal separation and molybdenum-antimony-ascorbic acid spectrophotometry was established in this study.The key parameters including extractant concentration,ultrasonic extraction temperature,ultrasonic extraction duration and centrifugal separation time were optimized to determine the optimal extraction conditions.Based on the molybdenum-antimony-ascorbic acid chromogenic principle,the calibration curve was established at a wavelength of 880 nm.The linear correlation coefficient of the calibration curve was 0.999 8,and the apparent molar absorptivity was 1.75×10⁴ L·mol^-1·cm^-1.The limit of detection(LOD) and limit of quantification(LOQ) of the method were 0.34 mg/kg and 1.36 mg/kg,respectively.The proposed method was applied for the determination of 4 certified reference materials(CRMs) for available nutrient analysis of soil available phosphorus.The relative standard deviations(RSD,n=6) of determination results ranged from 2.5% to 8.5%.The average values all fell within the uncertainty ranges of certified values,with relative errors(RE) of -4.61%-1.33%.The contents of available phosphorus in two typical soil samples from the Third National Soil Survey were determined according to the experimental method,and the recoveries were between 92% and 105%.Moreover,the available phosphorus contents in typical soil samples from the Third National Soil Survey were determined by the proposed method and the agricultural industry standard NY/T 1121.7-2014(the oscillation extraction is adopted for sample pretreatment),and the results of two methods were consistent.Compared with the standard method,this system presented significantly improved extraction efficiency,which provided efficient technical support for large-scale testing tasks such as national soil surveys.