Organic and Inorganic Sources
Organic and Inorganic Sources
Fertilizers may be divided into two broad groups: organic and inorganic, or chemical. An organic fertilizer is derived from a living plant or animal source. Nitrogen in an organic fertilizer is slow in becoming available for plant use because the organic nitrogen (NH2) must be reduced by micro-organisms to ammonium (NH4) or nitrate (NO3). Generally, home gardeners tend to use organic fertilizers more than commercial producers do because of their high cost per pound of actual nutrient element. 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 degree 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. High analysis, water soluble, chemical fertilizers will injury plants if not washed or brushed off the foliage.
Slow Release Fertilizers
Slow release fertilizers may be either inorganic or organic. They are characterized by a slow rate of release, long residual, low burn potential, low water solubility and they cost more than water soluble fertilizer.
The most common element in a slow release fertilizer is nitrogen. Several categories of slow release nitrogen fertilizers are commercially available, including:
--Urea-formaldehyde (UF) (38-0-0). Released by microbial degradation.
--Isobutylidene diurea (IBDU) (31-0-0). Released by soil moisture and particle size.
--Sulfur coated urea (SCU) (36-0-0). Release rate controlled by coating thickness.
--Plastic coated fertilizers (various formulations). Release dependent on temperature and coating thickness.
--Natural organics--sewage sludge, process tankage and fish scrap.
Unlike most granular inorganic fertilizers, which contain water soluble nitrogen (WSN), these slow release fertilizers are primarily composed of water insoluble nitrogen (WIN), which is released slowly. The majority of the slow release fertilizers offer both rapid initial release and long term release of nitrogen.
Soluble fertilizers have gained importance over the years in landscape management and nursery production. They are widely used to prevent and correct minor nutrient deficiencies. Soluble fertilizers are applied either on the foliage or on the soil.
Liquid fertilizers are important in production of nursery stock, particularly as additives in spray operations. Landscape and grounds personnel use liquid fertilizers extensively for deep root feeding of trees and shrubs.