黄土塬区不同土地利用方式下深层土壤水分变化特征

Soil water in deep layers under different land use patterns on the Loess Tableland

利用长期定位监测数据,对陕西省长武黄土塬区裸地、高产农田、苜蓿草地和苹果林地下0—15 m黄土剖面土壤水分环境进行了研究。结果表明,不同土地利用方式下,干湿交替层内土壤水分具有明显季节性波动变化特征,但其深度范围有别。裸地、高产农田、苜蓿草地和苹果林地分别约为0—5 m,0—4 m,0—2 m和0—3.5 m。干湿交替层以下深层土壤水分状况主要受土地利用方式的影响,其影响大小依次为苜蓿草地>苹果林地>高产农田>裸地,各土地利用方式下表现出不同的时间变化特征。黄土塬区土壤水量平衡计算中土层厚度大小的确定非常重要,这不仅与土地利用方式相关,也与林草植被的生长阶段相联。裸地和高产农田土层厚度选择不宜小于5 m和4 m;未形成深厚稳定土壤干层的苜蓿草地和苹果林地,土层厚度选择不宜小于15 m和10 m;对于已经形成稳定土壤干层的林草地来说,进行年尺度的水量平衡分析时,其计算深度可取降水入渗深度。研究可从土壤水资源的保持及利用的角度上服务于黄土塬区旱作农业的持续发展和土地利用方式的优化配置。

Soil water environment of 0--15 m loess profiles in bare land, high-yield farmland, alfalfa grassland and apple orchard on the Changwu Loess Tableland are investigated based on the data of long term experiments in situ. Results show that the seasonal variations of soil water were obvious in the layers of dry-wet alternation and the depths that the layers appeared were different under different land use patterns. The depths for bare land, high-yield farmland, alfalfa grassland and apple orchard were 0--5 m, 0--4 m, 0--2 m and 0--3.5 m, respectively. Soil water in deep soil layers below the layers of dry-wet alternation was mainly affected by land use patterns. In terms of the magnitudes of the effect, it showed in the order of alfalfa grassland〉apple orchard〉high-yield farmland〉bare land. And the temporal variations of soil water in deep soil layers were different under the different land use patterns. The determination of soil thicknesses is very important to the calculation of soil water balance on the Loess Tableland, depending on the land uses and the growth stages of the vegetations. The calculated soil thicknesses should be 5 m and 4 m at least in bare land and high-yield farmland, respectively and be 15 and 10 m at least alfalfa grassland and apple orchard, respectively when the stable dry soil layer has not yet formed in soil profile. However, when the layer has formed in planted woodland and grassland, the calculated thickness can take the depth of precipitation infiltration in the analysis of soil water balance at annual scale. This study can improve the sustainable development of rain-fed agriculture and the the conservation and utilization of soil water resources for the Loess optimal allocation of landuse patterns in the aspects of Tableland.