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.
