Urea fertilizer packs a powerful, nitrogen-filled punch into a small package. Urea granules are 46 percent nitrogen, one of the highest concentrations of nitrogen available in a fertilizer. It is also relatively inexpensive, making urea fertilizer a valuable resource for farming and gardening. However, overuse of nitrogen-rich fertilizers can contaminate waterways. Proper application of urea fertilizer is a necessity to prevent environmental problems. The amount of urea applied depends on the types of soil, the application method and the crop being fertilized.
Urea is 46 percent nitrogen. However, that nitrogen is not usable by plants immediately upon application. The urea must convert to ammonium, a plant-friendly form of nitrogen, through a series of reactions in the soil. Water and urease, a soil enzyme, break down the urea into usable ammonium. Depending on the soil temperature, the pH level and the amount of moisture in the soil, the reactions could be completed within a couple of days or take weeks to provide usable nitrogen to a crop.
Urea granules can be broadcast or applied with a seed drill in the seed row. Broadcasting scatters granules across the surface of the field quickly, but urea must be incorporated into the soil immediately to prevent nitrogen loss from runoff or through evaporation as the urea begins to break down. A seed drill drops granules into the soil along the seed row. As the urea begins to convert into ammonium, the soil near the fertilizer becomes toxic for a short time and may kill seeds and young seedlings. Keep granules away from seeds and seedling to prevent damaging plants. Additionally, urea can be dissolved in water and applied as a foliar spray on crops such as wheat, vegetables and potatoes. Dissolve one pound of urea per one gallon of water.
Before applying urea fertilizer, test the soil for nutrient content, pH level and moisture content. If the soil already has an adequate supply of nitrogen, adding more nitrogen will not improve your crop's growing conditions. Also, urea temporarily increases the soil's pH level but ultimately decreases it, making highly acidic soil more acidic. Many crops like more acidic soil, but check on your crop's favorite pH level before adding urea to the soil. Additionally, the moisture content of the soil affects the speed of the urea reaction. Dry soil slows the reaction, while moist soil speeds up the reaction.
Specialists at the University of Minnesota recommend applying urea at a rate of 10 pounds per acre at planting time when conditions are moist and at a rate of 20 pounds per acre when conditions are dry. Research from North Dakota State University suggests that applying urea at a rate higher than 20 pounds per acre at seeding time significantly reduces crop yield instead of increasing it. However, a study from the University of Minnesota showed that applying 160 pounds of urea per acre during the fall plow down produced about a 20 percent increase in crop yield the following growing season.