低丘红壤坡耕地的水分状况变化及其调控

红壤坡耕地水分状况随年降水周期、利用类型和坡位高低而变化。0~150cm土壤贮水量大致分为盈余期、消耗期和恢复期3个阶段。土壤水势变化与贮水量3阶段相对应,总体由大变小再回升,只是土壤剖面从上而下,水势值增大,变幅减小,100cm土层以下近乎常年稳定;在不同利用方式之间,土壤水势也有较大时空差异,花生地年际变化大,坡位上下差异小;板粟园恰好相反。在4个水势段出现频率中,水势高的水势段出现频率越高,顺序为饱和>湿润>亏缺>干旱;且饱和、湿润段出现频率比例总体上是板栗园>花生地,底土>心土>表土,坡下>坡上、坡中;低水势干旱段主要出现在坡上、土壤上层和伏秋干旱季节,出现频率比例依然是板粟园>花生地,尤其是中、下坡40~85cm心土层。由此,红壤坡耕地水分状况应因地制宜从工程、生物和农艺3方面予以调控。

WATER REGIME OF DRYLAND ON SLOPE OF RED SOIL LOW HILL AND ITS MANAGEMENT

Water regime in the 0 ~ 150 cm soil profile of farmland on slopes of red soil low hills changes along with cycle of precipitation of the year, type of landuse and position on the slope, forming into three stages, i.e. surplus period, depletion period and recovery period. The change in soil water potential coincides with that in soil water storage, showing the curve of a valley. Within the soil profile, soil water potential increases with depth, but decreases in variation amplitude. It remains almost unchanged throughout the year in the soil layer below 100 cm. Difference in landuse leads to sharp temporal and spatial difference in soil water potential. In peanut field, it varies greatly from year to year, but not much with position on the slope, while in chestnut garden it goes just the other way round. Of the four phases of soil water potential, i.e. saturation, wetness, deficiency and dryness, saturation is the highest in occurring frequency and they are often in the order of saturation > wetness > deficiency > dryness. On the whole, decreasing orders, like chestnut garden > peanut field, bottom soil > subsoil > surface soil, down-slope > upper slope and mid-slope, are observed in occurring frequency of the phases of saturation and wetness. The phase of dryness appears mainly in the upper slope, surface layer, summer and fall, but still shows a decreasing order of chestnut garden > peanut field, especially in subsoil, (40 ~ 85 cm deep) in the profile in the mid- and lower-slopes. Therefore, site-specific measures from the engineering, biological and agronomic aspects should be taken to manage soil moisture regime of the farmland on slopes of red soil hills.