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Abstract

A two stage method for preparing clear, storage stable, controlled release polymethylene urea nitrogen fertilizer solution. In the first stage, urea is reacted with a molar excess of formaldehyde, with temperatures of 75.degree. to 100.degree. C., at near-neutral pHs provided by buffers such as sodium bicarbonate, in the presence of ammonium compounds, until the formaldehyde is substantially converted to methylene moeities. In the second stage, the methylene moeities are reacted with additional urea and ammonium compounds, with temperatures of 75.degree. to 100.degree. C., in a near-neutral buffered solution at a pH of between 6.9 and 8.5, until the added urea is substantially converted to water soluble branched chain polymethylene ureas. Optimum urea to formaldehyde mol ratio in the first stage is between 0.483 and 0.518 to 1 and in the second stage optimum ratio is between 1.3 and 1.5 mols urea per mol of formaldehyde. The polymethylene ureas comprise a number of water soluble chemical compounds containing 2 to 4 methylene moeities, 2 to 5 urea moeities and 0 to 2 ammonia moeities including the different structural isomers for several of the same empirical formulae. The product formed by the two stage process contains little methylolurea and methylene diurea which are associated with reduced storage stability. Because of the two step process which provides low urea, ammonia and methylolurea concentrations, the product exhibits controlled nitrogen nutrient release to plants.

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