What is the first step in the nitrogen cycle?

The first step in the nitrogen cycle is often considered to be nitrogen fixation. However, the option relating to nitrification encompasses processes that follow nitrogen fixation. Nitrogen fixation converts atmospheric nitrogen (N₂) into ammonia (NH₃), which is then utilized by soil bacteria in the nitrification process to convert ammonia into nitrites (NO₂⁻) and then into nitrates (NO₃⁻).

While nitrification is a significant part of the nitrogen cycle, it's possible that the confusion stems from terminology and typical representations of the cycle. It's important to note that in the context of the choices given, nitrification is where the conversion of nitrogen occurs, making it a crucial process for assimilating nitrogen into a form that can be taken up by plants.

Assimilation by producers is a subsequent process where plants take up nitrates to build organic molecules, and denitrification returns nitrogen to the atmosphere but occurs after nitrification. Photosynthesis is unrelated to the nitrogen cycle directly as it pertains to carbon fixation.

Understanding this sequence highlights the role of nitrification following the initial fixation process, emphasizing its importance in making nitrogen available in a usable form for living organisms.