Estimating permanganate-oxidizable active carbon as quick indicator for assessing soil quality under different land-use system of rainfed Alfisols

Abstract

The labile fractions of soil carbon, often termed as active carbon pool serve as sensitive indicators of initial changes in soils due to management practices. A simplified method in which dilute, slightly alkaline KMnO4 reacts with the most readily oxidizable (active) forms of soil C was used to measure the labile fraction. The present investigation was undertaken in long-term experimental plots in Alfisols soil at Hyderabad. The different land-use systems evaluated were Leucaena (L. leucocephala) plantation, sorghum (Sorghum bicolor)–castor (Ricinus communis) rotation in cultivated land, Cenchrus ciliaris grassland and an undisturbed bare soil as benchmark. Shaking of air-dry soil in 0.01M KMnO4 solution for 5 min. and addition of 0.1 M CaCl2 for enhanced settling of the soil after shaking produced consistent and management sensitive results. Significantly higher active carbon content was noticed under Leucaena plantation, followed by grassland, undisturbed bare soil and cultivated land and the values varied from only 2.7 to 3.4% of organic carbon. Higher infiltration rate, lower bulk density, higher water stable mean weight diameter (MWD) of soil aggregates and higher organic carbon content were recorded under plantation and grassland soil compared to the cultivated and undisturbed bare soils. The active soil C measured by this procedure was closely related to other soil properties, such as infiltration (r2 = 0.71), MWD (r2 = 0.60), bulk density (r2 = 0.76), dehydrogenase activity (r2 = 0.62), microbial biomass carbon (r2 = 0.66) and organic carbon (r2 = 0.53). This procedure has a scope for developing a user-friendly field kit to measure active soil carbon, which would serve as a sensitive indicator for management-induced soil quality