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Researchers have now developed a new time-released fertilizer that slowly discharges its cargo. When applied to rice fields in Sri Lanka, crop yields increased, even when only half the typical amount of nutrients was added.

[...] A popular fertilizer is urea, a nitrogen-rich organic compound found in human urine. Urea is water soluble and volatile, which means that irrigation or a rain squall often sweeps it away in surface run-off or it escapes as a gas before it can be absorbed by plants. "Up to 70% of urea is lost to the environment,"

[...] The researchers attached urea molecules to hydroxyapatite—a constituent of human bones and teeth—in a six-to-one ratio by weight. The chemical bonds between the urea and hydroxyapatite molecules prevent the urea from decomposing too quickly. Yet, they do break down over time, which results in a controlled release of nitrogen at a rate that plants can absorb. Hydroxyapatite, which also slowly degrades, has the added benefit of being rich in phosphorus and calcium, elements that plants also need to thrive.

[...] The researchers then tested their fertilizer on a rice field in eastern Sri Lanka. They measured rice yields in three sections of a field: one that received no fertilizer, one fertilized with 100 kilograms of nitrogen per hectare of pure urea, and one fertilized with 50 kilograms of nitrogen per hectare from the urea-hydroxyapatite combo. The rows fertilized with the urea-hydroxyapatite duo yielded roughly 10% more rice than those fertilized with only pure urea, the team reports in ACS Nano.

This new fertilizer is made in a one-step process with inexpensive chemicals, unlike other controlled-release fertilizers on the market, such as polymer-coated urea. It's approximately 20% more expensive than pure urea, the researchers estimate. But it still may wind up saving farmers money, the authors contend, because it also delivers phosphorus and calcium, nutrients that normally have to be delivered by yet another set of fertilizers. "We believe that this novel formulation will be economically viable," Kottegoda says.

Source: http://www.sciencemag.org/news/2017/02/slow-release-fertilizer-boosts-crop-yields-reduces-environmental-damage
Full paper: http://pubs.acs.org/doi/full/10.1021/acsnano.6b07781

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