Urea, however, a synthetic organic fertilizer that is 45 percent N, is available at a low cost. In moist media at a temperature above 60 degrees F, it takes only about three to five days for the complete conversion of urea to ammonium. Another organic fertilizer that may soon be used in greater quantities is sewage sludge. Plants have been shown to respond favorably when sewage sludge was applied to the soil. Further research is needed before specific recommendations will be made.
Chemical fertilizers are either mixed or manufactured and have the advantage of low cost.
Consequently, most fertilizers used today are from chemical sources. They are characterized by a slow rate of release, long residual, low burn potential and low water solubility, and they cost more than water-soluble fertilizer. The most common element in a slow-release fertilizer is nitrogen. Released by soil moisture and particle size. . Release dependent on temperature and coating thickness. .