Abstract

Soil organic matter (SOM) in any agro-ecosystem is regulated by interaction of factors that determine its formation and promote decomposition, with a relative importance as: management > climate > biota > topography = parent material > time. Different land use practices under diverse climatic conditions in Hassan district (Karnataka) were selected for the study. Land use systems receiving frequent biomass additions through litter viz., Forest systems (both natural and manmade) and coffee plantations were observed with surface organic layer with higher SOC (10.6-13.2) content (g kg -1 soil). Agricultural systems mainly paddy, potato, vegetable, coconut and mulberry systems sparse OM additions were observed with reduced and lower SOC status (4.6-6.6). Humic acid (HA) and fulvic acid (FA) under these land use systems were dependent on land management i.e. source, form, amount, rate of organic materials added to soil. The HA fraction ranged from 0.2 g 100 g-1 soil in soils of coconut and paddy systems to 0.4 g 100 g-1 soil in natural forests. Quantitatively higher HA in forest and coffee systems was observed than agricultural systems. Proportionately to total SOM content (%), the HA was higher in agricultural soils (24.4-28.0) than coffee and forest soils (19.6-20.7). The systems with tree vegetations (forests and coffee) recorded higher proportions of FA (29.4-30.5) than agricultural systems like potato (26.5) and paddy (27.4). Forest systems with litter biomass additions (fresh organic materials) were with higher FA content while, agricultural systems receiving with almost decomposed OM (FYM) indicated higher HA than FA.

Keywords: Land use system, soil organic matter, humic acid, fulvic acid.