Variations in N mineralization and herbaceous species diversity due to sites, seasons, and N treatments in a seasonally dry tropical environment of India

Nitrogen (N) is an essential element for plant growth, however enriched N deposition may have seriously impacts on air, water, soil and vegetations. In this reference, we assessed the impacts of N applications on the rates of N-mineralization and their counter effects on the composition and diversity of herbaceous vegetation in a seasonally dry tropical environment of India. For this; 135, 1 × 1 m plots distributed in 15 locations were established at the Banaras Hindu University, India. Since 1st January 2007, within each location, equal numbers of 1 × 1 m plots were treated with three doses of N (0 kg N ha−1 yr−1/control, 60 kg N ha−1 yr−1 and 120 kg N ha−1 yr−1). Soil and vegetation samples were collected in year 2010. The data on soil N mineralization, rainfall and species numbers were collected monthly and the data on Shannon diversity index were collected seasonally. The data were subjected to appropriate statistical analyses. The NMS ordination suggested that the sites, N levels and seasons caused substantial differences in the rate of soil N-mineralization, species composition and diversity of herbaceous species. Results showed that moderate levels of rainfall and N applications (60 kg N ha−1 yr−1) facilitated the accumulation of herbaceous species diversity by accelerating the process of soil N-mineralization due to increased availability of soil–N and decreased C:N ratio of the soil. The study did not support the N-saturation theory for the N-mineralization rates as well as species diversity possibly due to loss of added N through the process of volatization, denitrification and consumed by the nitrophilic species, which warrants in-depth study of microbial dynamics to explore the mechanisms associated with N mineralization in N perturbed ecosystems, particularly from dry tropical environments of India which are nutrient and moisture limited.

► Soil moisture and N treatments changed the herbaceous species composition.
► Moderate level of fertilization enhanced the N mineralization and species diversity.
► Study did not support the N saturation hypothesis.