Evaluation of Coconut Based Gliricidia sepium Agroforestry Systems to Improve the Soil Properties of Intermediate and Dry Zone Coconut Growing Areas.

This study was intended to assess the potential of using coconut based G. sepium agroforestry systems to improve soil fertility of degraded coconut lands in intermediate and dry zones of Sri Lanka. Study locations were Rathmalagara Estate and Pallama Estate of Coconut Research Institute of Sri Lanka, which belong to Andigama soil series in low country intermediate zone (IL1) and Ambakele soil series in the low country dry zone (DL3) respectively. Experiment was conducted in a randomized complete block design with five treatments and three replicates. Main treatments were coconut based agroforestry systems intercropped with G. sepium, and sole coconut. A fallowed land and a sole G. sepium land were used as benchmarks. Soils from three depths i.e. 0-15 cm, 15-30 cm and 30-45 cm were analysed for its’ chemical, physical and biological properties. Results showed a significant (p < 0.05) accumulation of soil organic matter (SOM) due to incorporation of G. sepium. Mean SOM in top soil of G. sepium intercropped fields were 0.87% compared 0.49% in sole coconut, however values were quantitatively low compared to typical fertile soils. Higher soil total nitrogen (TN) was observed in G. sepium intercropped lands in both estates compared to sole coconut in same climatic zone, however quantity varied on degree of management of G. sepium such as lopping frequency. Exchangeable potassium (K) and magnesium (Mg) were observed in significantly high quantities in G. sepium intercropped fields than sole coconut. Significantly higher soil microbial activity (SMA) was observed in G. sepium managed and unmanaged conditions in both estates in contrast to sole coconut. This study reconfirms the promising results of integrating G. sepium for replenishing soil fertility of degraded coconut growing soils in intermediate and dry zone.