Relationships between pH, electrical conductivity, and organic matter content of paddy cultivated soils in Sri Lanka

Abstract

Rice (Oryza sativa L.) is widely cultivated as a low-land crop in most of the Asian countries. To cater the increasing demand for food, large extent of paddy lands is being cultivated using external inputs, such as crop residues, organic matter, and inorganic fertilizers. In order to improve and/or maintain higher crop productivity, soil conditions need to be maintained at favorable range required by the crops. Some of the key soil factors determining the productivity are soil organic matter content (OMC), soil pH, and electrical conductivity (EC). Therefore, the objectives of this study were to determine soil OMC, pH, and EC of selected Sri Lankan paddy soil samples and to develop relationships between those variables. A total of 35 soil samples representing paddy fields in Gampaha (20), Rajanganaya (7), and Polonnaruwa (8) areas were collected. The pH and EC of each soil sample were measured using pH and EC meter using 1:5 soil: water ratio. The OMC was determined using Walkley--Black method. Regression and correlation analyses were performed to study the relationships between these variables. There was a moderate negative relationship between soil pH and organic matter content (R2=0.130 p<0.05), and a moderate positive relationship between EC and organic matter content (R2=0.361p<0.05). With the increase of OMC soil pH was reduced due to the release of organic acids, and EC was increased due to the increased cation pool. These relationships between soil pH, EC and OMC need to be considered in sustainable soil management.