Abstract:
Rice (Oryza sativa L.) is cultivated largely using external inputs such as inorganic fertilizers and
pesticides. Apart from that, the addition of crop residues, organic matter, organic fertilizers, or soil
amendments are also required to enhance the productivity of rice farming. Usually, organic matter
content in soil is determined by Walkley and Black method which is costly and uses carcinogenic
chemicals such as potassium dichromate. In order to avoid these disadvantages, soil organic matter
content can be determined by obtaining the weight loss through ignition of soil samples using muffle
furnace. Therefore, this study was conducted to determine the fidelity of ignition method compared
to the chemical method for the determination of soil organic matter of selected paddy soil samples
in Sri Lanka. A total of 35 soil samples were collected representing paddy lands in Gampaha (20),
Rajanganaya (7) and Polonnaruwa (8) areas. Then the organic matter content of each soil sample
was tested using both Walkley and Black method and ignition method. In the Walkley and Black
method, organic matter content was determined by the oxidation of soil using potassium dichromate.
In the ignition method, soil samples were heated to 375 °C for 3 hours using muffle furnace.
Regression and correlation analysis were performed to study the relationship between two methods.
According to the results both methods made close estimations of the organic matter content i.e.
regression coefficient of 0.95 with a R2 of 0.89. Moreover, ignition method slightly underestimated
(6%) the organic matter percentage compared to the chemical method. As the soil organic matter
content determined using both methods were in good agreement, ignition method can be used as an
alternative method for the testing of organic matter in paddy soil samples.
