Abstract: "Slope-wall effect" has a significant role in diminishing snowfall freeze injury of Citrus sinensis var. sekkan planted on terraced mountainous fields with a definite degree of slope-wall.Investigations show that freeze injury starts to be diminished on fields with a 53.8皁f slope-waIl and is diminished signifi-cantly on those with a 80.6皁f slope-wall. Minimum freeze injury can be found on fields with a 86.1? of sIope-wall,but on fields with a 35.6皁f slope-wall,the freeze injury is nearly the same as control. Understanding and applying "slope-waIl effect" theory has a positive meaning in defensing and fighting freeze injury of Citrus planted On mountainous fields.

Key words: Heihe River Basin, land use, management measure, soil animal community, soil salinization, ecological threshold.