Introduction
Urea fertilizer, an industrial compound that is a principal source of nitrogen for crops in modern agriculture, is composed almost entirely of nitrogen, carbon and oxygen – the atoms needed to make plants. It’s made from carbon dioxide and ammonia under high pressure, a process first invented in the first half of the 20th century.
The story of urea fertilizer starts in agriculture with its first industrial production via the Haber process in 1828 by Friedrich Wöhler, which is also sometimes seen as a watershed moment for agricultural science. I always found it remarkable that, despite its discovery, for some time people used urea only in small quantities in agriculture. This was due to its high cost – improvements in the Haber process, notably expanding ammonia production, which then could be used to make urea, in the early 1900s made urea fertilizer cheaper and more widely available for farmers all over the world.
The scale on which urea fertilizer helped to increase crop yields was truly revolutionary and helped drive the agricultural boom of the 20th century.
It’s indubitable that without it, the global food need couldn’t be covered completely. Despite its importance, the link between the chemical characteristic or its history of biological science and its actual function or practicing in modern farming systems might not be clear.
Advantages of Using Urea Fertilizer
The first asset of urea as a fertilizer is the high proportion of nitrogen contained in it. Nitrogen is an important ingredient of the chlorophyll compound that allows plants to convert solar energy into chemical energy. As chlorophyll is the ‘soup’ from which plants grow leaves and develop, it is a crucial factor of agricultural productivity. Urea weighs around 46 per cent nitrogen, making it one of the most concentrated nitrogenous fertilizers commercially available. As a result, with an equal application of urea fertilizer, less product is applied to the land compared with other nitrogenous compounds.
Moreover, urea fertilizer is an inexpensive option. It is less costly to make and buy than most other nitrogen sources largely because of its high nitrogen content and the efficiency of the production process. As a result, it is an economical choice for the farmer desiring the highest yield for the money being invested. Helen S Hamilton, an agricultural economist, says: ‘Globally, urea remains the fertilizer of choice in terms of profitability and the biggest cost advantage, and particularly agronomic efficiency.
Furthermore, the form and flowability of urea fertilizer makes it simple to handle and apply. It typically comes in granular form, which is easier to store and spread over large agricultural fields than liquid fertilizers. When stored, urea fertilizer does not carry the risk of combustion or decay that some other fertilizers do. The solid form might be easier to spread mechanically, making it easier to integrate into modern farming operations and thereby saving valuable time and resources.
Disadvantages of Using Urea Fertilizer
However, urea has several disadvantages besides potential for increased production, such as increased efficiency and improved soil health. One of the major disadvantages is that there is volatilisation (improper use of nitrogen), which leads to loss of nitrogen. When urea is applied in the soil, it gets converted to ammonia gas, which is catalysed by an enzyme called urease found in the soil. This gas evaporates to the atmosphere if not retained quickly by soil moisture, which results in a loss of N in the atmosphere and lowises the efficacy of the fertilizer.
Another is the risk of over-application and its environmental consequences. Because of its high nitrogen content, overuse of urea has the risk of intensifying nitrogen leaching into waterways, contributing to water pollution and potentially eutrophication. These environmental consequences disturb local ecosystems and can contaminate drinking-water supplies – health risks for human populations. ‘Overuse of urea runs the risk of intense nitrogen runoff, which can disrupt aquatic ecosystems – sometimes this leads to algal blooms that can oxygenate water bodies,’ warns Emily F Stone, a soil scientist.
Furthermore, as urea fertilizer changes soil pH and the activity of microbes, it can lead to an erosion of soil health in the long run. While the breakdown of urea releases ammonia, this process increases soil alkalinity over time. As soil pH changes, it can affect the availability of other soil nutrients and restrict the growth of many important soil microorganisms. These shifts made to microbial communities can affect soil life and structure, leading to reductions in soil fertility and soil structure over time, which will in turn reduce plant growth and agricultural yields.
Urea Fertilizer and Environmental Concerns
The influence of urea fertilizer on the environment is not confined to the immediate vicinity of application, but can effect broader-scale ecological systems in a number of different ways. Most pressing is the impact on water bodies via runoff and leaching. Excessive or poorly managed applications of urea leads to nitrogen moving via leaching, into groundwater, and via runoff, into surface water.
This deposition of nitrogen into water bodies leads to the pollution of water systems, the primary causative agent of eutrophication in lakes and rivers due to the process of enhanced algal and aquatic plant growth, and the subsequent starvation of oxygen for aquatic life from the decomposition of material.
Another big transparency issue is the accounting for urea fertilizer in terms of greenhouse gas emissions as it degrades in soil to release nitrous oxide, an extremely potent greenhouse gas. It has a global warming potential almost 298 times that of carbon dioxide in a 100-year window.
Urea production also creates sodium hydroxide, a form of lime that is mixed with urea in the final production process. This waste byproduct is often dumped, leaks into rivers and contaminates water, polluting the landscape. Together with oil byproducts and carbon emissions from transport, these factors threaten the sustainability of urea fertilizer.
In response to these challenges, numerous regulations and environmental guidelines have been put to address challenges and promote safe use of urea fertilizer, which include minimising nitrogen loss and environmental pollution. Environmental guidelines and best practices recommend application of nitrification inhibitors with urea application to reduce nitrous oxide emission to the atmosphere and improve nitrogen use efficiency.
‘Regulatory regimes and best practice guidelines are critical tools where there is inherent tension between crop productivity and ecological stewardship,’ Mark A Bradley, a global expert in environmental policy, says. ‘Farmers must become equipped with the requisite knowledge and tools to apply urea responsibly.’ These measures would ensure that the enormous benefits conferred by urea fertilizer is harnessed without any adverse consequences for the environment.
Best Practices for Using Urea Fertilizer
To reduce urea fertilizer’s negative effects while maximising its benefits, best practices should be used. Volatilisation should be minimised through better nitrogen efficiency. For example, if urea is applied during cooler temperatures with higher humidity, less ammonia gas is formed. If urea is worked into the soil instead of left on the surface, urea volatilisation is reduced, and more nitrogen will be available for plants.
Other fertilisation practices for balanced nutrition that feed the soil are also important. Combining urea with organic fertilizers, or other mineral nutrients, improves the health and nutrient status of soils, increasing the effectiveness of urea and enhancing sustainable soil-management by boosting microbial diversity and soil structural quality.
The importance of technology in precision agriculture is the final pillar of best practices. Modern technologies include controlled-release fertilizers and precision-application equipment that help to spread urea in a more targeted way, ensuring that the right amount of fertilizer is applied at the right time and in the right place. Less fertilizer will be lost and more harvested. This will improve yield and preserve the environment.
‘The way farmers use nitrogen and their yields can change dramatically if they integrate precision agriculture tools to their systems,’ says John K Harrison, an agricultural technology specialist at the International Center for Tropical Agriculture’s Africa hub in Nairobi, Kenya.
If farmers take measures to accomplish this, then they’ll get the best out of urea fertilizer, boosting their crop productivity and doing so in a way that supports overall protection of the environment.
Conclusion
To summarise, urea fertilizer is the most widely used N fertilizer in the world. The very high N content and good price performance make it an essential part of modern agriculture. Nevertheless, there are also shortcomings and some negative consequences for the environment, if excessive concentrations of urea get to the soil and water bodies. The necessary innovations in the future to overcome these problems will lead to N‐use efficiencies and a reduction in environmental risks in agriculture.
The path forward for sustainable agriculture includes adopting more ecologically friendly practices for applying urea fertilizer. Current efforts to use precision agriculture technologies, including smartphone apps and satellite imagery, will help to reduce overestimation of nitrogen needs by farmers and the consequent wasted applications of excess fertilizer. In addition, the development of new highly stabilised urea formulations offers more opportunities for calibrating the flow of nitrogen release to meet the actual field needs of plants.
This delicate balancing act can’t be achieved if urea fertilizer is mismanaged and mishandled, and instead becomes a tool of environmental destruction. The future of farming begins with our recognition that we can no longer continue farming without making crucial changes to our farming practices. The very life of our planet depends on it.
Here’s a list of references that discuss the advantages and disadvantages of urea fertilizer：
- Trenkel, M. E. (2010). Improving Fertilizer Use Efficiency: Controlled-Release and Stabilized Fertilizers in Agriculture. Paris: International Fertilizer Industry Association. This reference discusses methods to enhance the efficiency of fertilizers like urea and includes sections on environmental impacts.
- Fageria, N. K., & Baligar, V. C. (2005). Enhancing Nitrogen Use Efficiency in Crop Plants. Advances in Agronomy, 88, 97-185. This article provides detailed insights into nitrogen use efficiency in crops, particularly focusing on urea.
- Sutton, M. A., Oenema, O., Erisman, J. W., Leip, A., van Grinsven, H., & Winiwarter, W. (2011). Too much of a good thing. Nature, 472(7342), 159-161. This publication discusses the challenges of nitrogen as a pollutant, particularly from agricultural sources like urea.
- Food and Agriculture Organization of the United Nations (FAO). (2020). Fertilizers as water pollutants. This FAO document outlines the pollution potential of fertilizers including urea and the regulatory measures to control their environmental impact.
