Urea solutions have been extensively investigated for foliar fertilization and have found significant commercial application in many uses. However, their acceptance has been limited by the risks of crop damage and loss due to unpredictable phytotoxicity. Many crops are unacceptable for prime markets if the foilage or fruit is marked or disfigured. Foliar fertilizers can cause such results. The phytotoxicity of urea solutions is notably random in that identical dosage rates (pounds of nitrogen per acre) of identical solutions often exhibit substantially different toxicity levels. One solution may cause no damage whatever and serve the grower's purpose admirably, while another may cause significant damage and economic loss.
Even with these drawbacks there is considerable interest in foliar fertilization with urea. The method allows rapid assimilation of the major and minor nutrients, antibiotics or other plant-treating agents. Assimilation through the foliage is more rapid than is root assimilation from soil applied nutrients. It is not uncommon that minor deficiencies of micronutrients or major nutrients require rapid correction. Soil application is often unable to satisfy these needs. Some micro- and major nutrients, and other agents such as insecticides, etc., are customarily applied to foliage. It would be convenient and less expensive to apply nitrogen in the same step and avoid duplication of effort, schedule conflicts and the cost of multiple crop treatments.
It is therefore one object of this invention to provide an improved foliar nitrogen source. Another objective is the provision of aqueous urea solutions of lower phytotoxicity, corrosivity, and increased storage stability. Another objective is the provision of aqueous urea solutions which can be foliarly applied with little or no phytotoxic effects. Another objective is the provision of an improved method of supplementing nitrogen by foliar fertilization.