Comparative study of soil aggregation, carbon and microbial dynamics under agro-forestry, grasslands, orchard and cultivated land use systems

Abstract

Land use has a profound impact on soil aggregate stability, carbon (C) sequestration and soil microbial activities. This study tried to explore the dynamics of soil C pools, aggregation, aggregate occluded C, microbial biomass and enzymatic activities within soil aggregates under four types of land uses viz. cultivated land, orchard, social/agro-forestry and grasslands. Outcomes indicated the maximum presence of total C in undisturbed soils of natural ecosystems like social/agro-forestry system (6.35 g kg-1), followed by orchard (4.05 g kg-1), grassland (4.03 g kg-1) and cultivated lands (3.07 g kg-1). Nevertheless, the proportion of water extractable C (WEC) + hot water extractable C (HWEC) per unit total C in soil was highest in tilled arable lands (0.128) and orchard (0.113) followed by social/agro-forestry (0.104) and grasslands (0.048). Although, land use showed no significant impact on soil microaggregates, macroaggregate quantity followed the order: social/agro-forestry (523.8 g kg-1 of total aggregate amount)> grassland (469.9 g kg-1)> orchard (454.1 g kg1 )> cultivated lands (332.7 g kg-1). Macroaggregate associated C was also found highest in soils of social/ agro-forestry (61.5 g C kg 1of macroaggregate), followed by grasslands (50.8 g kg 1), orchard (49.5 g kg-1) and cultivated lands (37.1 g kg-1). Analysis of microbial biomass C, present within the water stable aggregates, showed the same trend of macroaggregate quantity with land use change, while it was not so for the soil enzymatic activities. Analysis of both the dehydrogenase and βglucosidase enzymes showed their presence in the following order: cultivated soils> orchard> social/agroforestry> grasslands. It was postulated that these enzymatic activities were controlled by the proportionate presence of labile C (WEC and HWEC) in soils.