Abstract: The growth characteristics of 20-year-old alfalfa (Medicago sativa L. L.) and soil water consumption and recovery process at various eco-sites in semiarid Loess Plateau were systematically studied.Results show that alfalfa productivity varies with growth stages.Alfalfas have higher aboveground biomass from June to August,which is the vigorous growth period of a year under synchronous conditions of both temperature and precipitation.However,the soil water is excessively consumed to its bottom point.Alfalfa annual yield has significant difference.Alfalfa grows vigorously during 4 to 8 years in all tested ecosites.In the 10th year,soil water drops to the minimum level and reaches a severe deficit.Dry soil layer reaches 300～720 cm.After 10th year,soil water begins to recover slowly with alfalfa growth declining.Soil moisture above 500 cm soil layer recovers the same level as before planting in 15^th to 20^th years.However,the soil below 500 cm is seriously dry,and soil water recovery is extremely slow and hard.Overall,alfalfa production reaches peak during 4～8 years after planting,and alfalfa should be replanted at 8 to 10 years after planting in semiarid Loess Plateau.

Key words: Alfalfa, Aboveground biomass, Soil water, Dry soil layer, Semiarid region

摘要： 本文系统研究了黄土高原半干旱地区不同立地条件下,20年生紫花苜蓿(Meducagi sativa L.)生长变化特征与土壤水分的消耗与恢复过程。结果表明:紫花苜蓿不同生长阶段生产力差异较大,年生长的6-8月份,即在水热同步条件下,紫花苜蓿形成较高地上生物量,为年生长的盛期,但土壤水分消耗过度,降至年最低点;紫花苜蓿产草量不同生长年限均达极显著差异,在山地、塬地和川地3种立地条件下均呈规律性变化特征,即在生长的4～8年间,3种立地条件下紫花苜蓿均为旺盛生长阶段,第10年土壤含水量降到最低,土壤干层厚度高达300～720 cm,土壤水分严重亏缺;10年后随紫花苜蓿的基本衰败,土壤水分开始缓慢恢复;第15～20年,3种立地类型500 cm土层以上土壤水分可恢复到接近种植前的土壤含水量,而500 cm以下土壤通体干燥化严重,水分恢复极为缓慢,且恢复难度较大。因而,在黄土高原半干旱区紫花苜蓿适宜生长年限应为8～10年,第4～8年为苜蓿生长的高峰期。

关键词: 紫花苜蓿, 地上生物量, 土壤水分, 土壤干层, 半干旱区