Sustainability-minded processes of fertilizer nutrient recovery and more sustainable forms of fertilizer, such as the use of nanoparticles is being studied. For example, a "green" fertilizer production method that uses less harsh polar organic acids, such as citric acid, and mechanical size reduction of rock phosphate in wet slurries to produce a sustained-release nano-fertilizer formulation was recently patented. The fertilizer may be modified with urea to provide both phosphorus and nitrogen in slow release and soluble forms. The described nano-formulation provided performance in corn equivalent to commercial fertilizers but with a 50% reduction in dose. The "green" production process avoided the use of strong mineral acids, minimized water and energy use, and reduced waste. This provides evidence that, even using rock phosphate as a phosphorus source, sustainable manufacturing process can reduce fertilizer use and thus extend the useful life of phosphorus reserves. This is one type of solution to making rock phosphate supplies go further. The authors also claim the process can be used with other phosphorus sources such as hydroxyapatite or fluorapatite, while added nitrogen sources include urea, ammonium nitrate, ammonium sulfate, calcium nitrate, monoammonium phosphate, diammonium phosphate and potassium nitrate as possibilities to be incorporated into nanocomposites with phosphorus sources.