Soil Humic and Fulvic Acid Fractions Under Different Land Use Systems

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.

Impact of Diverse Agricultural Land Uses on Soil Organic Matter Fractions: A Comprehensive Evaluation

“…This is primarily attributed to the high plant density and dense vegetation canopy in rubber plantations, contributing to the elevated levels of these organic matter fractions. The SOM content tends to be higher in tree-based land use systems which in turn contributes to the increased concentration of SOM fractions [5]. This is confirmed from the positive correlation obtained between SOM and its fractions such as humic acid (r= 0.97***), fulvic acid (r = 0.97***) and humin (0.96***) as shown in Fig.…”

“…The humic substances present in any soil system is influenced by a multitude of factors, including its input from various sources and the subsequent loss due to decomposition. Despite their inherent resistance to biological degradation, changes in land use types and management practices have the potential to alter the chemical composition of humic substances [5].…”