National estimates of environmental thresholds for upland soil phosphorus in China based on a meta-analysis

Abstract The environmental threshold for upland soil phosphorus (P) content (ETSP, i.e., inflection point of soil P content leading to enhanced P loss) provides an important metric for guiding agricultural nonpoint source P pollution control. This study achieved the first meta-analysis to determine ETSP values for upland soils in China. The estimated national-level ETSP based on 472 field experimental observations of Olsen-P content and P loss rate was 30.1 ±4.0 mg P kg-1, which was lower than the average ETSP value (52.1 ±5.0 mg P kg-1) but higher than the average agronomic threshold values (16.0 ±6.4 mg P kg-1) previously reported. Lower upland ETSP values occurred in acidic soils and soils having higher organic matter content (SOM), precipitation and slope (ETSP: 30.5 for pH 56.4 for SOM 3%; 33 for precipitation 1200 mm yr-1; and 39.8 for slopes