COMPOSITION, DIVERSITY, AND BIOMASS OF HERBACEOUS SPECIES AND FUNCTIONAL GROUPS IN A GRADIENT OF NITROGEN AMENDMENT IN A DRY TROPICAL ENVIRONMENT OF INDIA

Nitrogen depositions due to anthropogenically induced disturbances are adding more reduced N to the biosphere, and have had considerable impacts on soil and vegetation. The objectives of the present study were to investigate the effects of N application on the diversity and biomass of herbaceous functional groups in a dry tropical environment of India. For this, a total of 135 1-m(2) plots distributed in five locations were established in the year 2007 on the campus of Banaras Hindu University, Varanasi, India. Each plot received a randomly chosen dose of N (0 kg N ha(-1) yr(-1) [control], 60 kg N ha(-1) yr(-1), or 120 kg N ha(-1) yr(-1)). Vegetation samples were collected in 2009 and 2010. The species diversity of each functional group in each 1-m(2) plot was calculated using the Shannon-Wiener index, and peak shoot biomass of the same was established by harvesting. The data were subjected to appropriate statistical analyses. NMS ordination suggested that soil moisture and N amendment caused changes in species and functional group composition and diversity. Location, year, and N amendment all contributed to significant differences in species diversity and biomass. Species diversity was maximum in the 60 kg N ha(-1) yr(-1) treated plots, while herbaceous above-ground biomass further increased due to the increase in N dose. The increase in total herbaceous biomass along the N amendment was mainly due to an increase in the biomass of grasses as there was a decline in forbs and legumes.