The agronomic and environmental assessment of soil phosphorus levels for crop production: a meta-analysis

As an essential element of crop growth, phosphorus (P) plays an important role in maintaining agricultural sustainability and ecological balance. A quantitative understanding of agronomic and environmental soil P thresholds at the global scale is required to enhance P-use efficiency and crop productivity while preventing environmental P losses. To address this issue, we conducted a meta-analysis with 584 data observations from 175 studies in 326 locations to assess the critical soil P thresholds as related to crop type and soil properties. The results showed that the average agronomic soil P threshold across all crops was 19.36 mg·kg−1 and the threshold was highest for vegetables (mean = 30.04 mg·kg−1), intermediate for cereals (mean = 17.06 mg·kg−1), and lowest for legumes (mean = 9.30 mg·kg−1). In contrast, the mean environmental soil P threshold across soil textures was 48.56 mg·kg−1. The environmental soil P threshold was significantly affected by soil texture and followed the order of clay > loam > sandy soils. Agronomic soil P thresholds correlated negatively with climate variables including mean annual temperature and mean annual precipitation, and positively with soil organic matter content. The environmental P thresholds correlated negatively with soil pH. Gradient-boosted regression tree statistical model analysis suggested that crop type and soil texture were the most important determinants of the variation in agronomic and environmental soil P thresholds, respectively. This study provides a first quantitative assessment of agronomic and environmental soil P thresholds for different crops, climates, and soil textures and should help improve the management of cropland P worldwide.