Abstract: In order to explore the changes of exchangeable Ca（ECa）and exchangeable Mg（EMg）in soils under greenhouse vegetable cultivations,a comparative study was carried out with 43 pairs of soil samples gathered from greenhouse vegetable fields and their adjacent upland fields in Shenyang suburbs of China.The results showed that compared with upland soils the average content of ECa and Ca/Mg ratio in greenhouse vegetable soils decreased by 6.38% and 10.34%, respectively,while EMg increased by 4.74%.The Ca/Mg ratios in both soils were significantly correlated with soil ECa（（r=）0.721 and 0.757,respectively,n=43,P<0.01） , but not with EMg（r=-0.065 and -0.117,respectively,n=43）.The decrease of ECa in greenhouse soils may be attributed to the comparatively higher output of Ca from the greenhouse vegetable system,inadequate Ca supply in fertilization,and lowered soil pH,whereas the increase of EMg may be resulted from the pH value range（（5.0）—6.5）that suits the existence of Mg in exchangeable form in the soil,and the high concentrations of Ca²⁺,K⁺ and NH⁺4 that inhabit the selective absorption of Mg²⁺ by vegetables.

Key words: soil, exchangeable calcium, exchangeable magnesium, Ca/Mg ratio, greenhouse vegetable field