Soil matrix infiltration characteristics in differently aged eucalyptus plantations in a southern subtropical area in China

In this study, we improved the method for measuring soil matrix infiltration by using a surface-positioned double-ring infiltrometer. The soil matrix infiltration processes of four differently aged (1, 3, 5, and 7 years) eucalyptus plantations were measured in situ in a southern subtropical area in China. Soil matrix infiltration characteristics (SMICs), including initial infiltration rate (IIR), stable infiltration rate (SIR), and cumulative infiltration (CI), were calculated using the experimental data of the soil matrix infiltration process. The physical and chemical properties of layered soil (0–60 cm with an interval of 20 cm), including soil textures, buck density (BD), soil organic matter (SOM), and soil water stable macroaggregate (WSMA) closely related to infiltration, were analyzed. Results showed that the IIR (140.33–233.14 mm h−1), SIR (116.24–194.04 mm h−1), and CI (118.42–217.20 mm) decreased with increasing forest age. In addition, the SIR and CI of the 1-year-old eucalyptus plantation were significantly higher than those of the other plantations. The decrease trend of SMICs with forest age was attributed to the soil properties changing in the eucalyptus plantations. The clay content, BD, SOM, and WSMA increased and sand content decreased with increasing forest age, thus inhibiting the SMICs. The results of stepwise regression analysis showed that the sand content of topsoil (0–20 cm) was the main factor affecting IIR, and the clay content of deep subsoil (40–60 cm) was the dominant factor affecting SIR and CI. The in situ soil matrix infiltration measurement in eucalyptus plantations was achieved with the improved method, and the main influencing factors were clarified. The results enhance understanding of soil matrix infiltration and its effect on precipitation redistribution and are helpful in quantifying the water storage capacity of plantation soil.