Fertilizer Research: Slow-Release Nitrogen Benefits Plant Growth

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New research combines nanotechnology with urea fertilizers to improve results. Copyright image by Decoded Science, all rights reserved.

Urea, a component of urine, makes a great fertilizer – but it takes a lot to cover a field, and needs to be reapplied often. There’s a new study out that uses nanotechnology to reduce the amount of urea needed to fertilize a field, without reducing crop yields. This technology will benefit developing countries, which need to cut the cost of fertilizers while raising enough food to feed their people.

Nitrogen Fertilizer History

Ever since 1913, when the Haber-Bosch process made the commercial production of ammonia possible, production of nitrogen (N) fertilizers has been a part of modern agriculture. Since then, urea has become a common fertilizer, one that contains 46% nitrogen.

But urea disintegrates very quickly. Farmers must hurry to blend the urea (usually in granular form) into the field’s soil, or else ammonia gets released as gas into the air instead of breaking down as the nitrates the plants actually need. The farmers usually do this via a little irrigation water, but a new study has found that it’s possible to even further control the decomposition of urea in the soil. This new technique combines urea with a hydroxyapatite (HA) nano-particle (NP) matrix, which slows down the urea’s volatility, so that it is available to the plants for a longer time.

The new study targets HA NPs to carry urea because they have a high surface-area-to-volume ratio. Naturally occurring rockphosphate, which is used as a phosphorus fertilizer, happens to be an HA, and exhibits low solubility, so this study experimented with a nitrogen-phosphorus setup that could allow slow release of nitrogen along with Phosphorus.

Plants Need Phosphorus and Nitrogen

Nature maintains balance via many cycles that exist on Earth. We call these cycles, “ecological cycles” and it is because of these cycles that materials necessary for life keep circulating in the environment. A few examples of such necessary materials are nitrogen, phosphorus, sulfur and water.

Here we discuss the importance of nitrogen and phosphorus only, but all of the above-mentioned materials are important for the existence of life.

Nitrogen and phosphorus, in particular, are constituents of the building blocks of life; the amino acids. Plants, as primary producers of energy, are the ones who build essential proteins (that are made of amino acids) that are then consumed by the chain of consumers, to make the food chains.

Nitrogen is critical for plant growth. Image by Atanamir.

The Nitrogen Cycle

In order to understand how plants use nitrogen and phosphorus, we must first take a look at the nitrogen cycle. This will help us understand that making nitrogen a component of fertilizers is not a mere human solution to promote plant growth, but it already existed in nature. Finding clever solutions to incorporate more nitrogen in the soil is an effort to make the most of the nitrogen cycle.

In an ecosystem, nitrates are found in the soil and are used up by the plants to build proteins. Herbivores then eat those plants. The digested and excreted waste matter from the animal releases nitrogen. When those animals die and decompose, more nitrogen from the proteins returns to the environment as ammonia.

Bacteria decompose the waste material or dead bodies, but there are also “nitrifying bacteria” that convert ammonia to nitrate. Nitrate is the form of nitrogen which plants use. Free nitrogen and ammonia aren’t usable forms of nitrogen for plants.

Nitrogen for Plants

Nitrogen is strongly associated with plant growth. Not only it is a constituent of the green pigment of plants; chlorophyll, but also nitrogen is an important part of organic molecules essential to life such as protein and nucleic acid. Even some sugars (carbohydrates) contain forms of nitrogen known as amino sugars. These amino sugars combined with polysaccharides (un-sweet, insoluble carbohydrate) make muco-polysaccharides that can be found in epithelia and chitin.

To synthesize molecules essential to life, plants need to obtain certain materials, such as nitrogen. Nitrogen is a material that is greatly involved in protein synthesis; a process where amino acids join, one after the other to give rise to a poly-peptide chain. (Nitrogen is a constituent of amino acids, and proteins are made of polypeptide chains.)

Phosphorus and Plants

Let’s get back to the importance of one other component we discussed in the beginning of the article; phosphorus. Phosphorus has a nitrogenous base, and is a basic structural unit of nucleic acids like DNA. So, phosphorus is yet another basic molecule for life. It plays an important role in protein synthesis and cell division, and is an important part of the “energy currency” of cells; the ATP molecules. Phosphorus is taken up by the plants from soil in the form of an orthophosphate ion: either HPO4-2 or H2PO4.

New Methods to Create Better Fertilizers

Nitrifying bacteria exist naturally in soil to supply plants with required nitrogen (or nitrates), but with an increasing world population, hunger and nutrition issues are also on the rise. To cope with food scarcity, scientists keep working on coming up with better fertilizers so that agriculture is not just dependent on bacteria or other natural processes for getting nitrates in the soil.

The formation of urea fertilizer brings science closer to the solution and this study takes those efforts one step further. Optimizing the amount of urea so plants can consume essential nitrates even more efficiently, and preventing unnecessary loss of ammonia (and hence nitrogen) significantly improves fertilizer benefits for plants.

Additionally, this study aided the supply of another important nutrient for plants; phosphorus, by combining urea at the micro level with a hydroxyapatite. The HA of choice in this study also happens to be naturally occurring rockphosphate that already has an application of phosphorus fertilizer, creating a win-win situation with both constituents of hybrid nano-materials.

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