Abstract: Based on the  phenological observation data of apple trees from Tianshui Agro-meteorological Experiment Station in 2003-2009,  meteorological data from Maiji National Basic Meteorological Station in 1971-2009, and the apple’s yield data from Tianshui City in 1991-2009, a model of water suitability and water sufficient rate degree for apple trees was established to calculate the water requirement and water suitability degree of apple trees in their whole growth period, evaluate the water suitability for apple trees in the city, and analyze the correlations between the water suitability degree and apple yield in the city. The results showed that the water supply for apple trees in the city was under good condition, with the annual mean water suitability and water sufficient rate degree being 0.52 and 0.61, respectively. The water suitability degree in apple trees whole growth period decreased with time, being worse at vigorous growth stage but good at late growth stage. The water suitability degree decreased with ages at initial growth stage, varied little at vigorous growth stage, and increased at late growth stage. The correlation between the water suitability degree at initial and vigorous growth stages and apple yield was remarkable, but the correlation between the water suitability degree at late growth stage and apple yield was not significant. Using our established model could better evaluate the water suitability for apple trees in dry-farming areas of Northwest China, and provide scientific bases for zoning apple planting and irrigation.

Key words: Changbai Mountain, Co-occurrence of species, Soil fauna community, Altitude gradient