Abstract: Precipitation in the semiarid area of the Loess Plateau has a large inter-annual variety,and is also unevenly distributed every year.Improvement of forage grass covering pattern could not only reduce the water consumption in drought season,but also promote the ecological conservation benefits.The present work was conducted to investigate the effects of different grass species on soil water distribution in apple orchard.The field experiment was carried out at Qingyang Grassland Agriculture Experiment Station of Lanzhou University under four treatments of different grass species,i.e.Dactylis glomerata,Trifolium repens and mixed planting of these two species.Results showed that to plant orchard grass and the mixture could reduce soil moisture content in different layers in orchard under slight drought in spring,but the effect of planting T.repens on soil moisture content was not significant.During the period with moderate or severe drought in summer,the soil moisture content under forage grass mulching treatment was significantly lower compared with that in the clear tilled orchard.The values of evapotranspiration of the planted D.glomerata,mixed planting and T.repens orchard were 45.3,55.4 and 0.7 mm higher respectively than that of the clean tilled plots in growing season,but the effect of planted T.repens on evapotranspiration in growing season was not significant.Therefore,it is practical to plant the species with low water consumption (such as T.repens) for improving the orchard environment instead of the species with high water consumption (such as D.glomerata) on the semiarid Loess Plateau.

Key words: apple orchard, grass planting, soil moisture content, evapotranspiration, the Loess Plateau