In modern day agriculture, nitrogen (N) fertilizers are almost a necessity to aid plants in reaching their full potential for growth, however issues and challenges are currently found when practicing this technique.

This article focuses on the types of nitrogen fertilizers, on the ways N is lost and on the different methods this chemical element is managed by farmers.

N is of great importance for agriculture since it forms a major part of a plant’s structure and it is essential for the growth of chlorophyll, a chemical substance used in plants to absorb sunlight and provide energy for all the biological and chemical reactions happening within. Nitrogen, one of the primary plant nutrients, is absorbed by plants in the form of nitrates (NO3-), mostly because nitrates are highly soluble in water, which allows plants to easily absorb the mineral. 

Nitrogen fertilizers became very popular after the invention of the Haber-Bosch process. Nowadays, over half the food produced across the globe requires nitrogen fertilizers, according to ‘Crop Nutrition, Mosaic’. Therefore, the efficient use of nitrogen is not only important to prevent contamination of groundwater but also to maximise yields.

Nitrogen fertilizers are split into two kinds: ammonium fertilizers and manure-based fertilizers. Ammonium fertilizers can be applied directly onto plants, whereas manure-based fertilizers need to be mixed with upper soil layers as they volatize more easily if applied directly. If N were to stay in ammonium form, there would be no loss as they can attach to the soil and remain immobile, however nitrification is a natural process that causes ammonium to convert into nitrate, which is good for plant absorption, but also means the nitrogen can be easily washed out of the soil by leaching.

Other ways that nitrogen loss can occur is through denitrification and volatilization. In order to choose the correct N management method, it is essential to understand the soil type, as each type endures loses differently.

Denitrification is when nitrates are converted into nitrogen (N₂) compounds, which cannot be absorbed by plants. This process occurs in fine-textured or highly saturated soil, with high temperatures. Volatilization is when the ammonium converts into nitrogen gas and is lost to the atmosphere; this usually occurs in manure-based fertilizers, as mentioned above, and in very moist and warm soils when the fertilizers are applied on the surface rather than mixed in the soil.

One of the first steps in nitrogen management is to ensure that farmers use natural nitrogen found in manure from livestock. By storing the manure produced by livestock and applying it to the soil at the appropriate time, saves the expenses from purchasing nitrogen off farm.

Moreover, it is important to know the requirements of the crop before applying fertilizers since too much can lead to run off and too little will not have any effect on the plants.

To prevent leaching, fertilizers must not be applied near the surface or on sloping land as this leads to run off. Application rates must also be low enough and manure must be mixed into the soil almost immediately after applying. Buffer strips can be used to filter nitrates before entering surface water.

Furthermore, ensuring that soil temperatures are below 10 degrees Celsius prevents denitrification and volatilization. Nitrification inhibitors can also be used to slow down the nitrification process, allowing N to stay in ammonium form long enough to prevent leaching and to give plants enough time to absorb the required nitrogen.  

In summary, the practice of efficient nitrogen management is key to avoid eutrophication and reduce costs for the farmer as well as being environmentally-friendly, and to do this, a thorough knowledge of the soil type and the crop requirement is necessary.

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