Effect of deep ploughing on the water status of highly and less compacted soils for coconut ( Cocos nucifera L.) production in Sri Lanka

Abstract

Soil compaction limits soil water availability which adversely affects coconut production in Sri Lanka. Field experiments were conducted in coconut ( Cocos nucifera L.) plantations with highly and less compacted soils in the intermediate climatic zone of Sri Lanka. Soil physical properties of sixteen major soil series planted with coconut were evaluated to select the most suitable soil series to investigate the effect of deep ploughing on soil water conservation. Soil compaction and soil water retention with respect to deep ploughing were monitored during the dry and rainy seasons using cone penetrometer and neutron scattering techniques, respectively. Evaluation of soil physical properties showed that the range of mean values of bulk density (BD) and soil penetration resistance (SPR) in the surface soil (0–10 cm depth) of major soil series in coconut lands was from 1.38 ± 0.02 to 1.57 ± 0.07 g/cm 3 and 55 ± 10 to 315 ± 16.4 N/cm 2 respectively. The total available water fraction increased with clay content of soil as a result of high micropores. However, due to soil compaction, ability of soils to conserve water and to remain aerated was low for those series. Deep ploughing during the rainy and dry periods in highly compacted soils (BD > 1.5 g/cm 3 and SPR > 250 N/cm 2) greatly increased conserved soil water in the profile, while in less compacted soils (BD < 1.5 g/cm 3 and SPR < 250 N/cm 2) conserved water content was adversely affected. Soil water retention in bare soils of both highly and less compacted soil series was higher than that of live grass-covered soil. Amount of water conserved in ploughed Andigama series with respect to bare soils and grass-covered treatments during the severe dry period was 10.4 and 16.9 cm/m, while water storage reduction in the same treatments with ploughed Madampe series was 6.55 and 5.45 cm/m respectively. In addition, deep ploughing even in the effective root zone with live grass-covered highly compacted soils around coconut tree was favorable for soil water retention compared to that of live grass-covered less compacted soils.