Analysis of spatial and temporal variabilities in soil properties under an oil palm cultivated land in Dodangoda, Sri Lanka

Abstract

The impacts of oil palm plantations on soil properties were not exclusively studied in Sri Lanka. Therefore, the oil palm cultivation at Culloden estate in Dodangoda in Kaluthara district was selected as a suitable study area to evaluate the variability of selected soil physical and chemical properties. The main objectives of this study were to evaluate the impacts of oil palm cultivation on selected physical and chemical properties of soil and to analyze whether there is a significant difference between soil properties in the oil palm site and a reference site. The selected plantation was divided into 3 zones to study the variability in soil parameters within the oil palm land. Three representative sampling points from each zone were selected. A composite sample was prepared mixing the soil from each sampling point in a particular zone. Three reference samples were taken from an abandoned grassland, located 600 m distance from the oil palm land. Monthly sampling was done for six months. Oil palm cultivation had silty clay soil, and the reference land had silty clay loam soil. Soil pH, electrical conductivity, bulk density, organic matter content, nitrogen and phosphorus levels of the study site indicated a significant difference compared to the reference site (p<0.05, Generalized Linear model, followed by the Tukey’s pairwise comparison as a post-hoc analysis at 95% level of confidence). The highest mean pH level was observed from the reference site as 5.58, while the lowest pH value was reported from the oil palm cultivation as 5.46. Soil pH was statistically significantly lower in the study site than in the reference site. Electrical conductivity was statistically significantly lower in the study site than the reference site. Also, organic matter content was statistically significantly higher in the reference site than the study site. Regarding the soil nitrogen content (%), the reference site reported the highest mean value as 0.28%, which was statistically significantly higher than that of the study site. Phosphorus content was statistically significantly lower in the reference site than the study site. Also, soil bulk density was statistically significantly higher in the study site than in the reference site. Even within the study site, the soil physicochemical parameters varied significantly, however, a general trend of an increase or decrease can be seen depending on the type of physicochemical characteristics considered. Organic matter content in the oil palm site increased in August due to harvesting practices and fertilization practices. A significant increase in soil nitrogen content was identified in September, due to the addition of nitrogen-containing fertilizer. Higher Soil bulk density in oil palm land indicated a significant impact on the soil compaction in oil palm cultivations. In conclusion, the soil properties in the oil palm cultivation land were significantly different from those at the reference site. To minimize negative impacts and promote long-term sustainability, the implementation of sustainable agricultural practices is recommended.