Soil Fertility and Heavy Metal Characteristics under Next Generation Dryland Rice Cultivation at Different Altitudes

Purpose This study aimed to clarify the regulatory effects of altitude heterogeneity on soil fertility and heavy metal distribution characteristics under next generation dryland rice (NGDR) cultivation.

Methods The rice variety Dianheyou 615 was selected as the test material. Two cultivation treatments were established, including high-altitude (DRH) and low-altitude (DRL) dryland rice. Soil physicochemical properties and heavy metal contents were systematically determined. The entropy weight-improved TOPSIS model was used to evaluate the relative proximity of soil fertility and heavy metals. Combined with pollution index method, sensitivity analysis, and correlation analysis, the pollution risk and key influencing factors of soil heavy metals were analyzed, as well as the coupling relationship between soil fertility and heavy metals.

Results The soil pH, soil moisture (SM), soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in DRH treatment were significantly higher than those in DRL treatment, while the contents of nitrate nitrogen (NO₃⁻-N), ammonium nitrogen (NH₄⁺-N), and total potassium (TK) in DRH were significantly lower. The contents of Zn, Cu, Mn, and Cr were higher in DRH soil, while Cd content was higher in DRL soil, and there was no significant difference in Pb content between different altitudes. The relative proximity of soil fertility in DRH was significantly higher than that in DRL, and altitude was the dominant factor regulating soil fertility (η_p²=0.99, P<0.001). The single-factor pollution indices and Nemerow comprehensive pollution indices were all less than 1 and 0.7, respectively, indicating that all the farmland soil was at a clean level overall. Sensitivity analysis showed that TN and TP were the core indicators affecting soil fertility, and Cd was the key factor affecting relative proximity of soil heavy metals. Correlation analysis indicated that SOC, TN, and TP in DRH soil had significant correlations with most heavy metals, whereas NO₃⁻-N and TK were the dominant fertility indicators correlated with heavy metals in DRL soil.

Conclusion The high-altitude dryland cultivation mode for NGDR is more conducive to improving comprehensive soil fertility, and no obvious heavy metal pollution risk exists in soils under both altitude cultivation modes. This research provides a theoretical basis and practical support for the green planting of NGDR, soil fertility improvement and farmland ecological security guarantee in the mountainous areas of southwestern Yunnan.