Abstract: Rubber-based agroforestry in the humid tropical region is a strategy to alleviate land degradation and seasonal drought under rubber monoculture plantations. We analyzed the spatial characteristics of saturated hydraulic conductivity (K_s, a measure of soil water availability) under rubber-Alpinia oxyphylla agroforestry in the humid tropical region of Southwest China. The experiment was conducted in the Xishuangbanna Tropical Botanical Garden by establishing a permanent plot (25 m × 11 m) under a rubber-A. oxyphylla agroforestry. A total of 40 quadrats were established for measuring the K_s, soil bulk density, non-capillary porosity, and field water-holding capacity. The ordinary kriging interpolation, path analysis and geostatistics method were used to analyze K_s spatial distribution pattern, variation characteristics and its controlling factors in rubber-A. oxyphylla agroforestry. The K_s was significantly higher (P<0.01) in A. oxyphylla planting zone than in rubber planting zone, and K_s decreased with the increases of the distance from the A. oxyphylla planting zone. Affected by structural factors, both K_s and field water-holding capacity showed a strong positive spatial autocorrelation (nugget coefficient C₀/(C₀+C)≤25%). K_s was significantly negatively correlated with soil bulk density (-0.613, P<0.01), but positively correlated with non-capillary porosity (0.408, P<0.01) and field water-holding capacity (0.352, P<0.01). Results of the multiple linear regression analysis showed that soil bulk density was the main controlling factor for K_s, indicating that intercropping A. oxyphylla with rubber could reduce bulk density, enhance soil porosity, and thus improve soil water infiltration.

Key words: rubber, Alpinia oxyphylla, agroforestry, saturated hydraulic conductivity, spatial pattern, geostatistics.