宁南旱区紫花苜蓿土壤干层水分特征及时空动态

Moisture Distribution Characteristics and the Time-space Dynamics of the Soil Dry Layer in Alfalfa Farmlands in Arid Regions of Southern Ningxia

通过连续两年对宁南山区不同生长年限的苜蓿土壤深层水分进行测定，结果表明：①随着苜蓿生长年限的增加，土壤整体上干燥化程度加剧。2004年测定的4、7和12年生苜蓿地0～700cm土层平均含水率分别为5．30％、5．22％和5．01％，2005年测定的3、6和10年生苜蓿地0—800cm平均含水率分别为6．26％、5．60％和5．27％。3年生以后，苜蓿根系已达300cm以下，对300～800cm土层水分消耗强烈，而对300cm以上土层水分消耗减缓。②根据不同生长年限苜蓿土壤深层水分分布和动态分析，可将土壤剖面分为4个层次：降水蒸发易变层（0～100cm）、降水继续扩散层（100～300cm）、根系耗水干燥层（300～800cm）和深层储水调节层（800—1000cm以下）。③苜蓿在6年生前，耗水深度和干层厚度逐年迅速增加；6年生时耗水深度和干层厚度均超过1000cm，0～1000cm平均含水率仅5．73％，土壤水分亏缺严重；7—12年生苜蓿生长衰退，耗水深度和干层厚度有所减小，300—700cm干层湿度仅维持在4．00％左右，而800—1000cm水分有回升现象。

In two consecutive years, the study measured the deep layer soil moisture content of farmland on which alfalfa had grown for different periods. The study indicated that while alfalfa growth was prolonged the soil desiccation degree increased on the whole. In 2004, the average soil moisture content was measured to be 5.30% , 5.22% and 5.01% in 0 -700 cm soil of the farmlands with alfalfa growing for 4, 7 and 12 years respectively. In 2005, the soil moisture was measured to be 6.26% ,5.60% and 5. 27% in 0 - 800 em soil of farmlands with alfalfa growing for 3, 6 and 10 years respectively. After alfalfa growing for 3 years, alfalfa taproot has reached a depth below 300 era. So soil moisture at 300 - 800 cm deep was consumed intensely and 0 - 300 cm soil moisture increased than before. According to moisture distribution and dynamic characteristics analysis on deeper soil profile of alfalfa fields with different growth age, the soil profile can be divided into four layers： soil layer with moisture easy to be changed by precipitation and evaporation（0- 100 cm）, soil layer with precipitation continuing to seep （100 cm to 300 cm）, dry soil layer having water exhausted by alfalfa root system （300 - 800 cm） and regulated deep soil layer storing water（800 -below 1000 cm）. Before alfalfa growing for 6 years, its soil moisture consumption depth and thickness are increasing quickly each year. And while it is 6 - year- old, both items exceed 1000 cm, and water contained in soil severely decreases, and in 0 - 1000 cm soil layer the average moisture is only 5.73%. Alfalfa growth declines at its 7 - 12 growth age, soil moisture＇ s consumption depth and thickness are decreasing slightly, while moisture contained in 300 - 700 cm dry soil layer only maintain 4.00% level, and in 800 - 1000 cm deep layer soil moisture has increased.