Land use change: A key ecological disturbance declines soil microbial biomass in dry tropical uplands

Land use changes such as transformation of natural landscapes, forest degradation and increase in croplands due to human activities are considered amongst the most influential ecological disturbances affecting soil, ecosystems and environmental sustainability. The previous works from India are limited to show that soil disturbances influence abiotic and biotic factors along a rural-urban gradient. However, variations in soil microbial biomass (SMB) -C, -N and -P quantity due to land use changes at different soil depths across different land use types remain poorly understood on comparative ground. We investigated the impact of land use types on soil properties and SMB -C, -N and -P levels across different soil depths (0-10, 10-20 and 20-30 cm) in dry tropical uplands. Four land use types/covers (natural forest, mixed forest, savanna and agriculture land) were selected. The present study is based on two hypotheses: i) different land use types affect SMB levels in top surface soil (0-10 cm), but have less effects in deeper soil profiles (20-30 cm); and ii) SMB levels in top surface soil are highest in natural forest, followed by mixed forest and then savanna and agriculture lands. ANOVA showed significant differences in SMB values due to land use covers (P < 0.001), soil depths (P < 0.001) and land use types × soil depths interaction (P < 0.001). Although, there had no effect of land use types on SMB levels in deeper soil profiles (20-30 cm) but soil parameters (soil pH, soil moisture, soil temperature, total-N, C/N ratio and organic-C) significantly affect SMB levels in top surface (0-10 cm) soil. The study suggests that SMB may be considered as a key indicator of soil fertility index, while land use practices are a major cause for loss of microbial community composition/biomass in dry tropical upland soil.