Soil Factors Exert Larger Independent Explanatory Contributions than Climate to Regional Rubber Yield Variation in Hainan Rubber Plantations, China

Objective: Hainan is an important natural rubber planting area in China. Due to topographical influences, rubber plantations in Hainan exhibit a distinct east–west distribution. The factors driving the differences in latex yield between the eastern and western regions remain unclear. This study aims to quantify the effects of climatic and soil factors on rubber yield in these regions, identify key factors, and provide a scientific basis for developing region-specific rubber plantation management strategies. Method: This study is based on 409 rubber plantation samples collected over a continuous 15-year period in Hainan Province (eastern region (n = 252) and western region (n = 157)). We analyzed regional differences in multiple indicators including soil pH, organic matter (OM), alkali-hydrolyzable nitrogen, available phosphorus, and available potassium, and core climatic variables (mean annual temperature, MAT; mean annual precipitation, MAP) between eastern and western Hainan. We further explored the relationships between these factors and rubber latex yield and identified the key yield-limiting factors for rubber plantations in different regions. Result: The yield per plant in the eastern region (3.38 kg) was significantly higher than that in the western region (3.25 kg). In the eastern region, annual precipitation (1707.78 mm), soil organic matter (24.43 g kg−1), alkali-hydrolyzable nitrogen (73.64 mg kg−1), and available potassium (42.73 mg kg−1) were all significantly higher in the eastern region than in the western region (1604.76 mm, 15.14 g kg−1, 60.75 mg kg−1, and 24.55 mg kg−1, respectively); while the annual mean temperature (24.02 °C) and soil pH were significantly lower than in the western region (24.17 °C, 4.81). Univariate quadratic regression revealed that both soil OM and AP exhibited significant positive correlations with rubber yield in western rubber plantations. However, after simultaneously controlling the joint variation of all climate and soil variables via multivariate stepwise regression, only OM was retained in the final predictive model. Conclusions: The key factors influencing rubber yield vary by region, with soil pH being the primary factor in the eastern region and organic matter in the western region. We explicitly differentiate two effects: short-term regional yield variations are mainly controlled by soil spatial heterogeneity rather than current climate differences, while long-term climate drives spatial divergence in soil fertility via pedogenic processes. The differences in key limiting factors between the eastern and western regions identified in this study provide data support and a scientific basis for formulating precise soil management plans for rubber plantations in Hainan Province, thereby promoting cost savings, efficiency gains, and sustainable development in Hainan’s rubber industry.