陕北黄土区人工刺槐林地土壤水势特征

为了研究黄土区人工林地土壤水分特征曲线及土壤水势特征,以陕北黄土区人工刺槐林地为研究对象,利用中子水分仪和中国科学院地理科学与资源研究所设计的负压计,对其2015年4月1日—2015年10月31日0—200cm土层的土壤含水量和土壤水势进行了连续观测,并运用灰关联法分析了表层(0—40cm)、中层(50—120cm)、深层(130—200cm)及4—10月土壤水势灰关联度。结果表明:(1)陕北黄土区人工刺槐林地各土层土壤水分特征曲线可用Gardner模型幂函数方程θ=aS-b进行拟合,拟合参数a值大小为表层土壤(0.103 8)中层土壤(0.094 4)深层土壤(0.086 0);b值大小为表层土壤(0.284)中层土壤(0.291)深层土壤(0.298)。(2)通过土壤水分特征曲线求得人工刺槐林地土壤水分常数,田间持水量和凋萎系数的平均值分别为25.53%和8.42%,最大有效水范围平均达17.11%。通常用土壤水吸力为0.1 MPa时,比水容量值来表征土壤供水能力,人工刺槐林地该值的大小表现为表层土壤(56.73%)中层土壤(53.74%)深层土壤(50.84%)。(3)人工刺槐林地土壤水势垂直空间分布表现为表层土壤水势从-0.21 MPa逐层增加到-0.08 MPa,中层土壤水势动态波动较大,整体呈下降趋势,深层土壤水势稳定在-1.14 MPa附近。灰关联度分析得出R12(0.899 8)R23(0.711 5)R13(0.702 8),人工刺槐林地土壤水势表层与中层关系较为密切,深层与中层关系次之,表层与深层关系最差。(4)人工刺槐林地0—200cm土层土壤水势,4—6月呈下降趋势,7—8月显著上升,9—10月再次下降。从各月土壤水势灰关联度来看,R_(10)(0.868 9)R_(05)(0.806 7)R_(09)(0.780 4)R_(07)(0.676 3)R_(06)(0.654 8)R_(08)(0.611 4),人工刺槐林地土壤水势10月,5月,9月变化态势与4月关联度较高;土壤水势7月,6月,8月与4月关联度较差。

A Study on Soil Water Potential Characteristics of Robinia pseudoacacia in North Shaanxi Loess Region

Soil water content and potential of the 0-200 cm soil profile in Robinia pseudoacacia forest land were observed continuously with a neutron moisture meter and a negative pressure meter to study the soil water characteristic curve (SWCC) and soil water potential characteristics in the Loess Hilly Region from April 1,2015 to October 31,2015,and the gray relational grade of soil water potential in different soil depths and months were analyzed by gray relational analysis.The results showed that:(1) Soil water characteristic curve (SWCC) at different soil depths could be well described by the Gardner power function.The fitting parameter a was in the order of the surface layer (0.1038) ＞ the middle layer (0.0944) ＞ the deep layer (0.0860),while parameter b followed the order of the surface layer (0.284) ＜ the middle layer (0.291) ＜ the deep layer (0.298).(2) According to the SWCC,soil water constant of the artificial R.pseudoacacia forest land was as follows:average field capacity and wilting coefficient was 25.53％ and 8.42％,respectively,and the maximum effective water range was 17.11％.Normally,when the soil water suction was 0.1 MPa,soil water supply capacity was characterized by the specific water capacity.The value was in the order of surface layer (56.73％) ＞ middle layer (53.74％) ＞ deep layer (50.84％) in the artificial R.pseudoacacia forest land.(3) The vertical spatial distribution of soil water potential of the artificial R.pseudoacacia showed that the water potential of the surface soil layer increased from-0.21 MPa to-0.08 MPa,the middle layer soil water potential fluctuated greatly,and the deep layer soil water potential was stable,being around-1.14 MPa.The grey relational grade analysis showed the order of R12 (0.899 8) ＞ R23 (0.711 5) ＞R13(0.702 8).The results showed that the relationship between the surface layer and the middle layer of the artificial R.pseudoacacia forest land was close,the relationship between the deep layer and the middle layer was the second,and the relationship between the surface layer and the deep layer was the worst.(4) Soil water potential of the 0-200 cm soil layers in the artificial R.pseudoacacia forest land decreased from April to June,then increased significantly from July to August,and decreased again from September to October.Thegrey relational grade of soil water potential in each month showed the order of R10 (0.868 9) ＞ R05 (0.806 7) ＞R09(0.780 4) ＞ R07 (0.676 3) ＞ R06 (0.654 8) ＞ R08 (0.611 4).The soil water potential variation trends in May,September,and October were similar to that in April.In contrast,the soil water potential variation trends in June,July,and August were different from that in April.