Abstract:
Objective This study aimed to investigate the evolution patterns of different forms of potassium (K) and clay mineral composition with plantation age and associated influencing factors in tropical rubber plantation soils, in order to provide a scientific basis for K management and sustainable production in rubber plantations in tropical regions of China.
Method Four rubber plantations with different ages (10 a, 20 a, 30 a and 40 a) were selected from the main rubber producing areas in the west of Hainan Island, and soil samples were collected at depths of 0 ~ 20 cm, 20 ~ 40 cm, 40 ~ 60 cm, 60 ~ 80 cm and 80 ~ 100 cm. Soil physicochemical properties and the contents of different forms of K were analyzed. Clay mineral composition was determined using X-ray diffraction (XRD).
Result Water-soluble K (WSK) and exchangeable K (EK) were both influenced by planting age, soil depth and their interaction. WSK showed an increasing trend with planting age in the 0 ~ 20 cm layer, while EK exhibited a decreasing trend with increasing soil depth. Slow available K (SAK) and total K (TK) were significantly influenced only by planting age, with TK being significantly lower at 10 years compared to 20 ~ 40 years. As planting age increased, the relative content of kaolinite decreased, while that of hydromica increased, indicating a trade-off relationship between the two minerals. Correlation analysis revealed a highly significant positive correlation between EK and soil organic carbon (SOC), total nitrogen (TN), and carbon-to-nitrogen ratio (C/N), while TK showed a highly significant positive correlation with pH and C/N. WSK, SAK and TK contents exhibited a significant negative correlation with kaolinite content and a significant positive correlation with hydromica content.
Conclusion Planting age significantly influenced the different forms of K and clay mineral composition in soil. There was a shift form of kaolinite to hydromica with increasing age, leading to higher levels of different forms of K in soil. Increased SOC positively regulated EK. Therefore, organic matter fertilization should be utilized to enhance K effectiveness. The research findings can guide the scientific management of K in rubber production.