Determination of the relationship between organic carbon and environmental factors in agricultural Saraburi soils by comparative analysis of methods

Abstract

Soil organic carbon content was important for soil properties, and processes include the accumulation of carbon affected by climate change. SOC was commonly measured by dry combustion with automated analyzers or a wet chemical oxidation method such as Walkley & Black method. The dry combustion technique was accurate and uncomplicated, but the cost was high. On the other hand, the Walkley & Black method was less expensive than dry combustion but needed a correction factor because of its underestimation of SOC content. However, correction factors had variability across study areas depend on soil type, management practices, and environmental parameters. This study aims to i) measure SOC stocks and investigate the associations between Walkley & Black and dry combustion methods ii) determine the relationship between SOC derived by both Walkley & Black and the dry combustion method and environmental factors such as pH, electrical conductivity (EC), nitrogen (N), and available phosphorus (P) in the agricultural soil of Saraburi. To compared different methods, we used 30 soil samples from the cropland area in Saraburi Province. The techniques used to measure SOC were the Walkley & Black and dry combustion method. The results showed mean±SD concentration values were 1.55±0.51% for the Walkley & Black method and 2.03±1.08% for the dry combustion technique. The percentage recovery (R) of SOC by the Walkley & Black method to the dry combustion technique varied between 44.4% to 114.6%. The correction factor (100/R) ranged between 0.87 and 2.25. In addition, there was a strong linear relationship for SOC content between the Walkley & Black method and dry combustion technique (r2 = 0.675, p < 0.001). The SOC exerted a significantly positive effective effect on the pH and EC value, but negative relationship on available P content (p < 0.01). The multiple regression equations were presented to predict SOC analyzed by Walkley & Black method and dry combustion technique from pH, EC, and available P values in agricultural Saraburi soils. The results of this study indicated that the choice of assessment methodology is a critical decision for the suitable quantification of SOC content. This work has established equations between SOC content and pH, EC, and available P values in agricultural Saraburi soil for the SOC estimation.