ROLE OF Gliricidia sepium ON PHYSICAL IMPROVEMENT OF GRAVELLY SOIL

The Andigama soil series, which is widespread in coconut lands, is known to havepoor physical characters restricting palm growth and yield in die intermediate zoneof Sri Lanka. This study was carried out to investigate the possibility of improvingdegraded soil conditions of Andigama series by intercropping with Gliricidiasepium under coconut. Gliricidia sepium was established in a 45 year old coconutplantation in double rows of 2 m x 1 m and arranged in a Randomized Block Designwith four replicates. The effect on soil physical characters such as texture, bulkdensity, aeration capacity, moisture retention and root distribution pattern ofGliricidia sepium were studied.Results revealed that clay fraction cemented with gravel significantly increased( P < 0 . 0 5 ) bulk density (1.62 ± 0.07). It acts as a physical barrier and reducedreadily available water fraction in B horizon. The available water fraction in A, ABand B horizons decreased by 66% before reaching 1 bar (100 kPa) suction in 7, 9and 11 days respectively during the dry period. Root proliferation of Gliricidiasepium through hard layers significantly reduced the bulk density (P