Dataset for "Precipitation and soil pH thresholds regulate 40-year legacy phosphorus dynamics in cropland soils of the Sichuan Basin, China"

Conventional agricultural nutrient management assumes that fertilizer inputs are the primary driver of soil phosphorus (P) accumulation, and that strongly acidic soils maximize P retention via geochemical fixation. However, the effects of long-term climatic and edaphic factors on soil P dynamics at regional scales remain unclear. Based on 3,623 paired soil samples collected in the 1980s and 2010s across the Sichuan Basin, China, we identified key drivers of soil total P (STP) changes using a random forest model. The results showed that the regional mean STP changed from 0.43 to 0.68 g kg⁻¹, representing a net increase of 58%. Precipitation and soil pH change (ΔpH) were the dominant controls of long-term STP accumulation, with precipitation showing a relative importance of over 20% and a critical threshold at approximately 1,000 mm yr⁻¹. Above this precipitation threshold, hydrological export constrained P accumulation and offset the theoretical P-fixation capacity in strongly acidic soils. A nonlinear pH response pattern was detected, which indicated that net P accumulation was lowest at pH ~5.5 and peaked at 7.0–7.5. STP change was significantly and positively correlated with ΔpH under all initial pH conditions, indicating that soil alkalinization generally favored greater P preservation than acidification. These findings reveal the limitations of conventional P accumulation assumptions, and highlight the importance of spatially explicit nutrient management strategies that incorporate precipitation and pH thresholds to improve P use efficiency, mitigate environmental losses, and sustain cropland soil fertility.