短轮伐期桉树人工林土壤入渗过程模拟与变化特征

Simulation and change characteristics of soil infiltration process during the short rotation of eucalyptus plantation

中国南亚热带地区桉树种植面积广且轮伐期短,研究短轮伐期内土壤入渗能力的变化对探究水文循环与水土保持效益具有重要意义。以广西东门国有林场桉树人工林为研究对象,据轮伐期选择4个不同林龄(1、2、3和5 a)的尾巨桉第一代植苗林,测量3个土层(0~20、20~40和40~60 cm)的土壤理化性质和入渗过程。结果表明:1)随林龄的增大,在0~20、20~40 cm土层,入渗能力呈“降低—升高—降低”的规律变化;而在40~60 cm土层呈“升高—降低—升高”的规律变化。2)初始入渗率、稳定入渗率以及累积入渗量均与土层深度、土壤密度呈极显著负相关(P<0.01),与孔隙度和有机质呈极显著正相关(P<0.01)。3)Horton模型和通用经验模型对桉树人工林的土壤入渗过程拟合较好。综上,短轮伐期内尾巨桉人工林土壤孔隙度、密度和有机质含量变化导致浅层土壤(0~20 cm)的入渗能力整体降低,深层土壤(20~40、40~60 cm)的入渗能力整体升高。

[Background]Soil infiltration is an important process of forest water cycle.The plantation is an essential part of forests,and the change of soil infiltration capacity of plantation soil indicates the change of benefits on soil and water conservation.Because of the wide planting areas and short rotation of eucalyptus plantations in the southern subtropical area in China,soil infiltration capacities changing with forest age is meaningful to study the change of benefits on soil and water conservation and the hydrological cycle.[Methods]Our study focused on the plantation(Eucalyptus urophylla×E.grandis)in the State-owned Dongmen Forest Farm in the Guangxi Zhuang Autonomous Region of China.According to the rotation of eucalyptus plantation,four first generation eucalyptus plantations with differently forest ages(1,2,3,and 5 a)were selected for measuring the physical and chemical properties of soil particle size,soil bulk density,soil porosity,soil organic matter,and soil aggregate groups in three soil layers of 0-20,20-40 and 40-60 cm.The soil infiltration rate was measured by the cutting ring method with variable water head and the soil infiltration process was fitted by four common models.[Results]1)As the forest age increasing,the soil bulk density of four eucalyptus plantations ranged from 1.03 to 1.38 g/cm^(3)with a fluctuant increase trend.The soil total porosities of four eucalyptus plantations ranged from 47.84%to 60.96%with a fluctuant decrease trend and the soil organic matter content of foureucalyptus plantations ranged from 8.94 to 29.06 g/kg with a fluctuant increase trend,as the forest age increasing.2)Initial infiltration rate,stable infiltration rate,and cumulative infiltration had the significantly negative correlations with soil depth and soil bulk density(P<0.01),while these parameters had the significantly positive correlations with soil porosity and soil organic matter(P<0.01).Soil infiltration capacity at 0-20 and 20-40 cm soil layer had a changing trend of first rising and then decreasing with the increase of forest age,and soil infiltration capacity at 40-60 cm soil layer had a changing trend of first decreasing and then rising with the increase of forest age.3)Compared with the soil infiltration processes fitted by Kostiakov model and Philip model,the Horton model and the general empirical model were more suitable to well fit the soil infiltration process of eucalyptus plantation.[Conclusions]The soil porosity,soil bulk density,and soil organic matter were significantly affected by forest age during the rotation of eucalyptus plantations.Consequently,the soil infiltration capacity of the shallow soil(0-20 cm)had a whole decrease trend and the soil infiltration capacity of deep soil(20-40 cm and 40-60 cm)had a whole increased trend with the increase of forest age in eucalyptus plantations.Our results may provide a science basis for sustainable management of the eucalyptus plantations.