宁夏黄土区稀疏带状山杏人工林土壤湿度动态与影响因素

Soil Moisture Dynamics and the Influencing Factors in the Sparse Strip-Planted Prunus sibirica Plantation in the Loess Region of Ningxia

【目的】以宁夏南部黄土丘陵区带状山杏人工林为例,揭示林带内与带间的不同深度处土壤湿度的时空变化及其关键环境影响因素,为半干旱区林草植被科学管理及雨水资源高效利用提供依据。【方法】2020—2022年,在宁夏彭阳县山杏人工林带内和带间各布设1套200 cm测深的智墒传感器,分层逐时监测土壤体积含水量和土壤温度变化,同时布设1台气象站连续监测近地面降水、气温、空气湿度等气象条件,采用相关分析探究土壤湿度对前1日土壤湿度、土壤温度和气象因子的响应规律。【结果】2020年和2021年为平水年,降水量分别为467.4和440.8 mm;2022年为枯水年,降水量为354.8 mm;土壤体积含水量平均值为平水年(2021年,17.0%)显著高于枯水年(2022年,14.3%)。土壤体积含水量随土层加深呈近线性增加,其斜率表现为林带间高于林带内,平水年高于枯水年。在0~120 cm土层的土壤体积含水量为林带内(15.3%)高于林带间(14.0%),但在120~200 cm土层为林带间(17.6%)高于林带内(16.8%)。在0~60 cm土层的土壤体积含水量变异系数为林带间(42.9%)高于林带内(37.8%),但在60~200 cm土层为林带内(23.2%)高于林带间(19.1%)。土壤湿度变化的季节格局为:相对稳定期(3—4月)、耗损期(5—8月)、恢复期(9—11月)和衰退期(12月—次年2月),最大值多出现在4月,最小值出现在8月(平水年)和12月(枯水年);土壤湿度变化的垂直空间格局为:速变层(0~50 cm)、活跃层(50~90 cm)、次活跃层(90~170 cm)、相对稳定层(170~200 cm)。相关分析发现,土壤湿度日变化相关性最强的环境因子为正相关的前1日土壤湿度和负相关的土壤温度,月变化相关性最强的环境因子为负相关的土壤温度。【结论】宁夏黄土区稀疏带状山杏人工林林带内和林带间土壤湿度在季节和剖面上均表现出较大波动,枯水年比平水年波动的层次更深。综合分析发现前1日土壤湿度、土壤温度、气象因子均是影响枯水年和平水年日及月尺度各剖面层次土壤湿度变化的要素。其中,前1日土壤湿度和土壤温度为主要影响因子;在0~120 cm土层内的土壤湿度为林带内高于林带间。本研究结果对宁夏半干旱黄土区水平沟整地后退化植被科学恢复及土壤水分高效利用有很好的指导意义。

【Objective】With the sparse strip-planted Prunus sibirica plantation in the loess hilly region of southern Ningxia as an example,this study aims to reveal the spatio-temporal dynamics of soil moisture in different depths inside the forest belt(IFB)and between the forest belts(BFB)and the key environmental factors in order to provide a scientific basis for the restoration of forest-grass vegetation and efficient utilization of rainfall resources in the semi-arid area.【Method】From 2020 to 2022, two sets of 200 cm-depth soil moisture sensors were respectively installed at sites of IFB and BFB in Pengyang County, Ningxia, to monitor the changes of volumetric soil moisture and soil temperature by stratified hourly method. At the same time, a meteorological station was set up to continuously monitor the meteorological conditions, such as near-surface precipitation, air temperature, and air relative humidity. Correlation analysis was applied to explore the response of soil moisture to the previous day's soil moisture, soil temperature and meteorological factors. 【Result】Both 2020 and 2021 were ordinary years, with precipitation of 467.4 mm and 440.8 mm, respectively, while 2022 was a dry year with precipitation of 354.8 mm. The mean volumetric soil moisture in ordinary year (2021, 17.0%) was significantly (P<0.05) higher than that in dry year (2022, 14.3%). Volumetric soil moisture increased linearly with soil depth, and its slope in BFB was higher than that in IFB, and the slope in ordinary year was higher than that in dry year. Volumetric soil moisture in 0-120 cm soil layer was higher in IFB (15.3%) than that in BFB (14.0%), while that in 120-200 cm soil layer was higher in BFB (17.6%) than that in IFB (16.8%). The coefficient of variation (CV) of volumetric soil moisture in 0-60 cm soil layer was higher in BFB (42.9%) than tht in IFB (37.8%), while that in 60~200 cm soil layer was higher in IFB (23.2%) than that in BFB (19.1%). The seasonal patterns of soil moisture variation were able to be divided into the relative stable period (from March to April), the depletion period (from May to August), the recovery period (from September to November) and the decline period (from December to February of the next year). The maximum value of soil moisture mostly appeared in April, and the minimum value appeared in August (the ordinary year) and December (the dry year). The vertical patterns of soil moisture variation in the soil profile were divided into the rapidly changing layer (0-50 cm), the active layer (50-90 cm), the sub-active layer (90-170 cm) and the relatively stable layer (170-200 cm). The correlation analysis showed that the daily soil moisture was most correlated with the soil moisture at the previous day (positively) and the soil temperature (negatively). The monthly soil moisture was most correlated with the soil temperature (negatively). 【Conclusion】The soil moisture IFB or BFB of the sparse banded A. sibirica plantation in the loess area of Ningxia fluctuates strongly in seasons and profiles. The fluctuation in the dry year is deeper than that in the ordinary year. The previous day's soil moisture, soil temperature and meteorological factors are the key factors affecting soil moisture in each profile level on a daily and monthly scale in low-flow and ordinary-flow years. Among them, the previous day's soil moisture and soil temperature are the main factors, and soil moisture in 120 cm depth is higher in IFB than that in BFB. The results of this study have a great guiding significance for scientific restoration of degraded vegetation and efficient utilization of soil moisture after horizontal ditch soil preparation in the semi-arid loess area of Ningxia.