plant nitrogen cycle

Understanding Nitrogen Cycles For Healthy Crop Growth

plant nitrogen cycle hydroponic

A key component of fertilizers and heck, all of life, is nitrogen. It is a key building block of DNA for all living organisms. Without it, crops will struggle to remain healthy. Nitrogen develops tissue and cell growth within plants, forms chlrophyll by aiding plants to receive energy from light, and also helps plants create protein. A lack of nitrogen in a plant is usually shown by the following:

  • Stunted root systems and plant growth
  • Older leaves turn yellow
  • Low crude protein

However, farms have to be careful to not overcompensate and add too much nitrogen as this could have detrimental effects. Understanding the nitrogen cycle will help farms achieve their goal of accurate nitrogen usage.

The Different Stages of A Nitrogen Cycle

plant nitrogen cycle

1. Fixation

This involves the conversion of atmospheric nitrogen to a plant available form that is digestible by plants. This occurs either through an industrial process, as in the production of synthetic mineral salts, or a biological process, as with legumes such as alfalfa and clover, or in the case of soilless farming, through the usage of organic hydroponic nutrients.  Plant available nutrients, as nitrogen, phosphorous or other nutrient types, are so important because if the plant cannot absorb them through its roots it requires additional time and energy spent by microbes often to make it plant available by decomposing and mineralizing the organic matter (e.g. manure, compost, etc.) as you will learn about in the next section. We’ve mastered how to skip this process, turning organic hydroponic nutrients into fast release, so that the farm doesn’t have an abundance of nutrients that need to be flushed or at risk of sodium toxicity.

2. Mineralization

Microbes decompose organic nitrogen from manure, organic matter and crop residues to ammonium. The mineralization of microbes by nitrogen depends on how much nitrogen is present in the residues that they are decomposing. For many organic hydroponic nutrients, microbes are incorporated into the product, allowing this process to take place. Through the decomposition of the residue, the excess nitrogen is released as ammonium, one of the forms that is available for plant uptake.

3. Nitrification

In a non-chemical process, microorganisms would be put to work converting ammonium to nitrate to obtain energy. Nitrate is the most plant available form of nitrogen, but is also highly susceptible to leaching when over applied in soil.

4. Denitrification

This is what you would like to avoid. Nitrate is converted to nitrogen gas, thus removing bioavailable nitrogen and returning it to the atmosphere. This process only occurs where there is little to no oxygen, and the loss of nitrates in nutrients can prove to be detrimental and costly. In a soilless farm, one can spot when denitrification may be occurring when the pH of the water is highly acidic (less than 4). This will often indicate that your system, generally found within your water reservoir, growing media, and surfaces of your plants’ roots have anaerobic zones allowing microbes to compete, quite ruthlessly, for oxygen.

5. Volatilization

The loss of nitrogen through the conversion of ammonium to ammonia gas, which is released to the atmosphere. Volatilization losses are higher for manures and urea fertilizers that are surface applied and not incorporated (by tillage or by rain) into the soil. How this affects soilless farms remains to be largely measured. What we do know is that the nitrogen and ammonia losses caused by volatilization in soil farms would not be the same, we infer to be substantially less, given that there is increase efficiency with the mobilization of nutrients to the plants when water is the medium. Know more about this and would like to share? Can you reach us? 

6. Immobilization

This is the reverse of mineralization. If the carbon to nitrogen ratio of a residue material is higher than approximately 25 to one, the amount of nitrogen in the ratio is less than what the microbes need to build their biomass as they decompose in the residues.

7. Leaching

A pathway of nitrogen loss which is very problematic for water quality. Soil particles do not retain nitrate very well because both are negatively charged. As a result, nitrate easily moves with water in the soil, causing severe environmental impacts. For soilless farms that use a heavy amount of synthetic mineral salts, the inability to for the crops to fully retain the nitrate also means that it flows into the sewage systems when flushed. The frequency of flushing a soilless farm’s water reservoir to rid of any unused nutrients varies by farm size and best practices of each farm.

8. Crop Uptake

Achieving optimum nitrogen usage is about applying sufficient nitrogen at a time when the crop is needs it, dictated by the specific growth state and respective nutrient requirements of each crop type.

By growing an understanding of the nitrogen cycle that allows it to become available to crops, farm can be better stewards of its usage and see better ROI from their nutrient usage, while also lowering the carbon footprint as a result of using synthetic mineral salts. For soilless farms in particular, understanding how the nitrogen cycle applies to a growing method is key. We’re here to help.



Cornell University Cooperative Extension

Fondriest Environmental Monitor

Green As It Gets

The Nature Education

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