Dependence of Soil Organic Carbon on available Iron and Manganese Concentrations in Submerged Rice Soils

Dependence of Soil Organic Carbon on available Iron and Manganese Concentrations in Submerged Rice Soils

Effect of soil submergence on changes in soil organic C (SOC) and DTPA-extractable Fe and Mn and their interrelationship was studied in three texturally-different soils viz. loamy sand, clay loam and silty clay traditionally grown to rice-wheat system. Laboratory incubation experiments were conducted for 120 d under controlled temperature and moisture conditions. Soil organic C increased with incubation period up to 30-45 d and declined sharply thereafter. Similarly, concentration of DTPA-Fe was highest at 30 d and decreased sharply thereafter. However, DTPA-Mn concentration was the highest at 15 and 30 d of incubation, under submerged and field capacity moisture regimes, respectively. Soils incubated under submerged conditions exhibited higher SOC, DTPA-Fe, and DTPAMn than those incubated at field capacity moisture. In all the three soils under submerged conditions SOC, DTPA-Fe and Mn were higher at 40o C followed by 30o C and 20o C temperature. Irrespective of soil and incubation temperature, values of these variables did not change with incubation of air dry soil. The concentration of DTPAFe and Mn showed positive relationship with SOC concentration at submerged and field capacity moisture regimes. Increase in SOC with submergence was considered to be due to an increase in DTPA-Fe and Mn suggesting the need for using some chelating agents to remove their interference in SOC determination by wet digestion method..