# Chapter 3:1 Nitrogen The complexity of the nitrogen cycle and nitrogen’s importance in plant growth have made this element the subject of much research. The nitrogen cycle is a dynamic system that includes the water, atmosphere and soil. Plants require nitrogen more than any other essential element, excluding carbon, oxygen and hydrogen. Nitrogen is modeled by SWAT+ in the soil profile and in the shallow aquifer. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://swatplus.gitbook.io/io-docs/theoretical-documentation/section-3-nutrients-pesticides/chapter-3-1-nitrogen.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.