• # question_answer Nitrogen is available for plants in the form of: A)  Nitrogen gas  B)  Nitrogen dioxideC)  Nitrate           D)  Nitric acid

Nitrogen is present in the environment as organic nitrogen, ammonium, nitrite, nitrate, nitrous oxide, nitric oxide or inorganic nitrogen gas. Nitrogen is available to plants as either ammonium $(N{{H}_{4}}^{+})$ or nitrate $(N{{O}_{3}}^{-})$. Chemical processing or natural fixation (bacterial conversion) is necessary to convert gaseous nitrogen into compounds such as nitrate or ammonia which can be used by plants.