Are soil-adjusted vegetation indices better than soil-unadjusted vegetation indices for above-ground green biomass estimation in arid and semi-arid grasslands?

Accurate estimation of grassland biomass has been a central focus due to its importance in ecosystem processes and carbon cycles. This study aimed to examine whether the performance of soil-adjusted vegetation indices for estimating above-ground green biomass was better than that of soil-unadjusted vegetation indices in arid and semi-arid grasslands. Above-ground green biomass in desert steppe of Inner Mongolia and corresponding moderate-resolution imaging spectroradiometer (MODIS) surface reflectance 8-day composite MOD09Q1 data were collected during late September of 2013. Results showed that soil-adjusted SAVI (soil-adjusted vegetation index), MSAVI (modified soil-adjusted vegetation index), OSAVI (optimized soil-adjusted vegetation index), TSAVI (transformed soil-adjusted vegetation index), ATSAVI (adjusted transformed soil-adjusted vegetation index) and PVI (perpendicular vegetation index) did not improve estimation accuracy over soil-unadjusted simple ratio (SR) and normalized difference vegetation index (NDVI), due to low green vegetation cover (<30%) in the study area. Our results suggest that these soil-adjusted vegetation indices may be not suitable for describing green vegetation information in arid and semi-arid grasslands with low green vegetation cover (<30%).