What form of nitrogen do plants require?

Plants primarily require nitrogen in its inorganic form to support their growth and development. The most common inorganic forms of nitrogen that plants utilize are ammonium (NH4+) and nitrate (NO3-). These forms are readily absorbed by plant roots and are crucial for synthesizing amino acids, proteins, nucleic acids, and chlorophyll.

In contrast, organic nitrogen, which is found in decaying plant and animal matter, must first be converted into inorganic forms by soil microorganisms before it can be taken up by plants. Gaseous nitrogen, while abundant in the atmosphere, is not usable by plants in its diatomic form (N2) without first undergoing a process like nitrogen fixation, which some bacteria facilitate. Liquid nitrogen is not a viable source for plants as it is extremely cold and can cause harm to biological tissue.

By understanding that plants require inorganic nitrogen, it becomes clear why this is the correct answer. Inorganic nitrogen is essential for their nutritional needs and overall health.