The aim of this study is to investigate the activity of alkaline phosphatase (extracellular enzyme) in vertical and horizontal developing direc tions of rhizosphere (0-5 and 5-10) cm . The plots experiment is performed in College of Agriculture / University of Al-Qadissiya for the spring season 2013 ,the sandy loam soil is used to cultivate Tomato (Lycopersicon Esculentum mill) and Bean (Phaseolus Vulgaris L.) plants under salinity levels (without salinity , 6 , 8 and 10) dS.m-1 and compost levels (0,10 and 20)T.h-1 , their interactions completely randomized design (CRD) is used with six replicates, and the means of treatments are compared by L.S.D test 5% level .
The results are summarized as :
1- The enzyme activity are increased with increasing of the adding compost level 20Ton.h-1 and its interactions with salinity levels .
2- The enzymes activity are varied in rhizosphere development directions and the plants are differ in the site of highest activity , the enzyme activity in horizontal rhizosphere development direction is higher than the vertical direction .
3- The enzyme activity in bean rhizosphere is higher than in Tomato rhizosphere in activity except of the alkaline phosphatase at all rhizoshere vertical and horizontal directions .
4- The high inhibitor percentage of enzyme activity is at the level of 10 dS.m-1 salinity and the lowest is at the 6 dS.m-1 . The inhibition percentage are increased in vertical direction of rhizosphere developing (5-10)cm in tomato plant. The adding compost levels are varied by increasing or decreasing of enzyme activity according to rhizosphere development and it sites ..