This paper selects the Dingxi specific semiarid hilly areas in the middle of the Loess Plateau．Based on the former experiment practice，study on conservation tillage on soil water dynamic，crop dry matter and yields，water use efficiency etc，of 2 phase rotation systems with spring wheat and field pea，by the field experiments in dryland in 2002-2004．The results show： 1 The season and vertical dynamic ofwater storage in 2m soil profile are similar under ．conservation tillage and traditional tillage． 2 No-tillage with straw mulch enables to increase moisture retention．According to this paper,water storage normally increased by 7．02％一24．29％． 3 No—tillage with straw mulch enables to increase soil moisture by 0．53％-11．26％． 4 Different rotation sequences have different effects on water storage and soil moisture．Water storage increased by 2 1．72％-30．36％and 20．1 3％-30．92％respectively under 2 phases rotation systems．All of soil moisture of crops for rotation with field pea is higher than crop lower limit(CLL)． 5 Conservation tillage and rotation system are able to enhance soil porosity and infiltration rate． 6 Dry matter in later phase．Crop dry matter is increased by 7．1 6％一54．05％under crops for rotationwithfieldpeathanthatwith springwheat． 7 No-tillage with straw mulch Can increase the crop yield and water use efficiency．Compared with traditional tillage，they increased bY 30．28％and 40．08％respectively．

本文选择黄土高原陇中丘陵半干旱典型地区——定西地区，在前期试验研究的基础 上，2002年至2004年通过对保护性耕作条件下早地春小麦—豌豆双序列轮作试验农田土 壤水分动态、产量及水分利用效率等方面的试验研究，结果表明： 1、保护f生耕作与传统耕作0—2m土层贮水量的季节性变化及垂直变化趋势基本一致。 2、保护性耕作不翻耕土壤，利用免耕秸秆覆盖增加土壤的蓄水保墒能力，提高0—30cm 土层的贮水量7．02％一24．29％。