ROLE OF Gliricidia sepium ON PHYSICAL IMPROVEMENT OF GRAVELLY SOIL

The Andigama soil series, which is widespread in coconut lands, is known to have poor physical characters restricting palm growth and yield in die intermediate zone of Sri Lanka. This study was carried out to investigate the possibility of improving degraded soil conditions of Andigama series by intercropping with Gliricidia sepium under coconut. Gliricidia sepium was established in a 45 year old coconut plantation in double rows of 2 m x 1 m and arranged in a Randomized Block Design with four replicates. The effect on soil physical characters such as texture, bulk density, aeration capacity, moisture retention and root distribution pattern of Gliricidia sepium were studied. Results revealed that clay fraction cemented with gravel significantly increased ( P readily available water fraction in B horizon. The available water fraction in A, AB and B horizons decreased by 66% before reaching 1 bar (100 kPa) suction in 7, 9 and 11 days respectively during the dry period. Root proliferation of Gliricidia sepium through hard layers significantly reduced the bulk density (P resulted in improving aeration capacity, total and readily available water. Moreover, results showed that with the improved soil conditions by Gliricidia sepium, coconut root growth also increased by 5.3%, 9 1% and 2 1% in A, AB and B horizons respectively. These studies strongly suggested that Gliricidia sepium plays a major role in improving physical characters of infertile gravelly soils.