Effect of short term agroforestry systems on soil quality in marginal coconut lands in Sri Lanka

A study was conducted to assess the potential of using coconut based agroforestry systems to improve soil quality of marginal coconut lands and to screen out the efective perennial forest species in revitalizing the soil properties in intermediate of Sri Lanka. Experiments were conducted on Andigama soils in Rathmalagara estate of Sri Lanka to assess the infuence of short rotation forestry-based agroforestry production systems on the soil properties at marginal upland condition using eight forest plant species (Acacia auriculiformis, Calophyllum elatum, Macaranga paltata, Acacia mangium, Gliricidia sepium, Swietenia macrohylla, Bridelia moonii and Tectonia grandis). The highest value of soil organic matter (SOM) was observed in G. sepium planted plots (1.86%) followed by A. mangium (1.69%), while the lowest value was obtained for control plots (0.21%). Plots with N-fxing tree species had 30–50% higher total nitrogen concentration in the 0–40 cm soil than plots with non-N-fxing tree species. The highest value of total nitrogen (TN) was observed in A. auriculiformis plots (1.48 mg kg⁻¹) while the lowest was recorded in control plots (0.92 mg kg⁻¹). Exchangeable potassium was signifcantly higher in G. sepium planted plots (0.48 cmol kg⁻¹) as compared to other plots. The highest microbial activity (128.5 CO₂ µg g⁻¹ soil day⁻¹) was observed in A. auriculiformis plots, followed by M. paltata (102 CO₂ µg g⁻¹ soil day⁻¹), while the lowest activity was recorded in the control plots (65.56 CO₂ µg g⁻¹ soil day⁻¹). Signifcantly higher microbiological activities confrmed the symbiotic association of the studied tree species with soil microbes. These fndings provide preliminary evidence on the efectiveness of A. auriculiformis and G. sepium in revitalizing the soil properties of degraded coconut lands using short term agroforestry.