Haiqing Gong

Decades of fertilizer intensification have reshaped phosphorus (P) cycling across China's croplands, driving a widespread transition from P deficiency to enrichment while leaving spatially heterogeneous legacies of accumulated soil P. However, the long‐term trajectories of soil available P, their regional divergence, and the drivers regulating P accumulation or depletion remain poorly resolved at the national scale, limiting the development of sustainable and region‐specific P management strategies. Here, we integrate nearly 190,000 soil samples from harmonized national soil surveys with long‐term fertilization experiments to quantify long‐term soil available P dynamics across China at 1 km resolution and to assess the importance of key environmental and management drivers using an interpretable, spatially explicit machine‐learning framework. Soil available P increased sharply from 1980 to 2018, with an overall increase of 20.6 mg kg ⁻¹ , shifting from widespread deficiency to pronounced enrichment, particularly in eastern croplands. Long‐term experimental evidence demonstrates that sustained fertilizer inputs play a central role in driving soil P accumulation. Interpretable machine learning revealed spatial heterogeneity in the dominant drivers of soil available P change, with management effects strongest in Central China, and climatic and environmental influences more pronounced in the Northwest and Northeast. Sensitivity‐based future projections indicated divergent potential trajectories to 2060, with climatic changes reducing soil available P, whereas management intensification increased soil available P by approximately 13%. These findings show that long‐term soil available P dynamics across China are governed by the combined effects of fertilization legacies, soil‐environmental context, and climate, providing a national basis for region‐specific and sustainable P management.

Soil acid–base status fundamentally regulates biogeochemical cycling and agroecosystem resilience by controlling nutrient solubility, cation exchange, and redox equilibria. However, the long-term evolution of soil pH and its spatial divergence under intensive agricultural expansion remain poorly quantified. Herein, we integrate three nationwide soil surveys (1980, 2012, 2018) encompassing over 190,000 cropland observations into a harmonized 1 km dataset to reconstruct four decades of soil pH change across China. National mean soil pH declined from 7.1 in 1980 to 6.7 in 2012 and 6.6 in 2018, revealing a sustained acidification trend. Nearly one quarter of neutral soils (pH 6.5–7.5) have shifted into acidic classes (<6.5) since 1980, reflecting widespread depletion of soil buffering capacity under intensive fertilization, high rainfall, and carbonate exhaustion. By integrating current pH conditions with standardized pH change rate, we delineate nine bidirectional soil pH risk zones that capture contrasting acidification and alkalization processes along climatic and edaphic gradients. Acidification-prone zones dominate humid southern croplands, whereas alkalization risk prevails in arid northern regions. Our results provide nationally consistent, grid-level evidence of soil acid–base evolution across nearly four decades, offering a quantitative foundation for region-specific soil management to sustain productivity and mitigate environmental risks.

High-concentration phosphorus (P) fertilizers are crucial for crop growth. However, fertilizers with lower P concentrations, such as calcium magnesium phosphate (CMP) and single super phosphate (SSP), can also serve as efficient P sources, especially when blended with high-concentration P fertilizers like diammonium phosphate (DAP) or monoammonium phosphate (MAP). In this study, we conducted a 48-day pot experiment to explore how blending low-P fertilizers could optimize maize P utilization, using CMP to replace DAP in acidic soil, and SSP to replace MAP in alkaline soil, with five SSP+MAP and CMP+DAP mixtures tested. Key metrics such as shoot and root biomass, shoot P uptake, root length, and soil P bioavailability were measured. We found that maize biomass and P uptake with 100% DAP were comparable to those with 50% CMP and 50% DAP in acidic soil. Similar results were observed for 100% MAP compared to 50% SSP and 50% DAP in alkaline soil. Root biomass and length were largest with 100% MAP in acidic soil and at 100% DAP in alkaline soil, with no significant differences at 50% SSP or CMP substitutions for MAP and DAP, respectively. Furthermore, 50% SSP or CMP substitutions for MAP and DAP increased the content and proportion of the labile inorganic P (Pi) pool (H₂O-Pi and NaHCO₃-Pi), had a direct and positive effect on Olsen-P. Our findings reveal that 1:1 blends of SSP and MAP in acidic soil, and CMP and DAP in alkaline soil, effectively meet maize’s P requirements without relying solely on high-concentration P fertilizers. This indicates that strategic blending of fertilizers can optimize P use, which is crucial for sustainable agriculture.