Urea-formaldehyde solution for foliar fertilization

Abstract

A clear, storable, aqueous solution of partially condensed urea and formaldehyde substantially free of formic acid supplies non-burning and slow-releasing plant food nitrogen when applied directly to the foliage of living grasses, and agricultural and ornamental plants or to soils having neutral or acid surfaces. The substantially ammonia free solution has a pH between 7.5 and 9.8 and contains added buffering agents so that between 0.05 and 0.30 milliequivalents of phosphoric acid are required to reduce pH of one gram to 7.0; and is prepared by the partial condensation of from 1.5 to 2.0 mols urea with 1.0 mol formaldehyde for 20 to 300 minutes at temperatures between 75° and 90° C. with between 0.05 and 0.3 milliequivalents of alkali hydroxide per gram of solution as catalyst.

I claim: 
     
       1. A process for preparing a storage-stable aqueous solution of a urea-formaldehyde partial condensation product adapted for the foliar feeding of plants which consists of: providing an aqueous solution of an alkali metal hydroxide, urea and formaldehyde substantially free of formic acid, said solution having a urea to formaldehyde ratio of from 1.5 to 2.0, a nitrogen content between 10 and 30% and a pH between 8.5 and 9.8;   heating said aqueous solution at a temperature of from 75° C. to 90° C. for 20 to 300 minutes while continuously maintaining the pH thereof between 8.5 and 9.8 by the incremental addition of an alkali metal hydroxide until the reaction mixture exhibits a viscosity of from 10 to 60 centipose at 25° C.; and   cooling said reaction mixture to ambient temperature and adjusting the pH to between 7.5 and 9.8 by the addition of a water soluble buffering agent in an amount to provide a buffering capacity requiring between 0.05 and 0.30 milliequivalents of phosphoric acid to lower the pH of one gram of the reaction mixture to 7.0.   
     
     
       2. The process in accordance with claim 1 wherein said alkali metal hydroxide is sodium hydroxide or potassium hydroxide. 
     
     
       3. The process in accordance with claim 2 wherein said buffering agent is selected from the group consisting of sodium phosphate, potassium phosphate, potassium formate, ammonium phosphate, ammonium formate, triethanolamine formate, ammonium carbonate, sodium bicarbonate, and triethanolamine phosphate. 
     
     
       4. The process in accordance with claim 3 wherein said reaction mixture is heated at a temperature of from 80°-87° C. and wherein the pH of the reaction mixture is maintained between 9.0 and 9.7. 
     
     
       5. The process in accordance with claim 4 wherein the pH of said cooled reaction mixture is adjusted to between 8.0 and 9.0 by the addition of ammonium phosphate in an amount to provide a buffering capacity requiring between about 0.1-0.2 milliequivalents of phosphoric acid to lower the pH one gram of the reaction mixture to 7.0. 
     
     
       6. The aqueous fertilizer composition prepared by the process of claim 1. .Iadd. 
     
     
       7.  A process for preparing a storage-stable aqueous plant food adapted for the foliar feeding of plants, consisting essentially of forming a solution of partially reacted urea-formaldehyde that is primarily methylol ureas by heating a reaction mixture of water, alkali metal hydroxide, urea and formaldehyde substantially free of formic acid to a temperature of from 75° C. to 90° C. and maintaining the temperature for 20 to 300 minutes while maintaining the pH of the reaction mixture between 8.5 and 9.8 and until the reaction mixture exhibits a viscosity of from 10 to 60 centipoise at 25° C., the amount of urea and formaldehyde in said solution being selected to provide a urea to formaldehyde ratio of from 1.5 to 2.0 and a nitrogen content not less than 10% and not appreciably more than 30% by weight, said solution being buffered to a pH between 7.5 and 9.8 by the addition of one or more water soluble buffering agents in an amount to provide a buffering capacity requiring between 0.05 and 0.30 milliequivalents of phosphoric acid to lower the pH of 1 gram of the solution to 7 and being sufficiently reactive to allow further urea-formaldehyde reaction to form effective amounts of slow-releasing water-insoluble plant food nitrogen, without requiring addition of any materials, when the solution is cooled to ambient temperature and is applied to the foliage of plants or to soil having a pH ranging from about 5.0 to 7.5. .Iaddend. .Iadd. 
     
     
       8.  A process in accordance with claim 7, wherein the amount of alkali metal hydroxide in the solution is between 0.1 and 0.3 milliequivalents of alkali metal hydroxide per gram of solution. .Iaddend. .Iadd.9. A process in accordance with claim 8, wherein the reaction mixture is initially provided with between 0.05 and 0.15 milliequivalents of alkali metal hydroxide per gram of solution and said maintaining of the pH of the reaction mixture is accomplished by adding 0.15 or less additional milliequivalents of alkali metal hydroxide. .Iaddend. .Iadd.10. A process in accordance with claim 9, wherein said adding of alkali metal hydroxide is accomplished incrementally. .Iadd.11. A process in accordance with claim 7, wherein the reaction mixture is heated to a temperature of from 80° to 87° C. and the pH is maintained between 9.0 and 9.7 during the maintenance of said temperature. .Iaddend. .Iadd.12. A process in accordance with claim 7, wherein said buffering capacity is between about 0.1 and 0.2 milliequivalents of phosphoric acid required to lower 
     
     
        the pH of 1 gram of the solution to 7. .Iadd.13.  A clear, storage-stable, aqueous plant food solution comprising partially reacted urea and formaldehyde primarily as methylol ureas and with a ratio of between 1.5 and 2.0 mols urea per mol of formaldehyde, said solution having a nitrogen content not less than 10% and not appreciably more than 30% by weight and having a viscosity between 10 and 60 centipoise at 25° C., said solution being buffered to a pH between 7.5 and 9.8 by one or more buffering agents having a buffer capacity controlled so that between about 0.05 and 0.30 milliequivalents of phosphoric acid are required to decrease the pH of one gram of the solution to 7, and said solution being sufficiently reactive to allow further urea-formaldehyde reaction to form effective amounts of slow-releasing water-insoluble plant food nitrogen, without requiring addition of any materials, when the solution is applied to the foliage of plants or to soil having a pH ranging from about 5.0 to 7.5. .Iaddend. .Iadd.14. A plant food solution in accordance with claim 13, wherein said buffering agents are selected from the group consisting of sodium phosphate, potassium phosphate, potassium formate, ammonium phosphate, ammonium formate, triethanolamine formate, ammonium carbonate, sodium bicarbonate, and triethanolamine phosphate. .Iaddend. .Iadd.15. A plant food solution in accordance with claim 13, further comprising effective amounts of plant food potassium and phosphate. .Iaddend. 
     
     
        .Iadd.  .  An improved method for supplying nutrients to plants, said method comprising applying a plant food solution in accordance with claim 13 to the foliage of plants in concentrations and amounts required to produce desired plant growth rates. .Iaddend.