Plants require suitable pH, nitrogen, phosphorus, potassium and micronutrients to maintain vigorous growth. Oklahoma soils tend to be acidic in the east and north central parts of the state, and alkaline in the west and southwest parts of the state. The state's soils are mostly low in nitrogen and phosphorus, and especially low in potassium in the east. In winter before you begin planting, test the soil to determine the pH and nutrient content, then apply fertilizer based on the soil test recommendations. Fertilizers are categorized by chemical make-up and the amount of nutrients they make available to plants.
Organic fertilizers consist of dried or composted plant and animal waste. Examples include cotton seed, sewage sledge, manure, blood meal and bone meal. These materials are often mixed or ground to a powder during the manufacturing process. Organic fertilizers provide nutrients to plants slowly as microbes in the soil break down the organic nitrogen. Organic fertilizers cost more because larger quantities are needed to achieve the same effects as conventional fertilizers.
Non-synthetic fertilizers contain inorganic materials that do not undergo chemical processing. Limestone, rock phosphate and potassium chloride serve as examples of non-synthetic fertilizers because they are mined and marketed as is. Like organic fertilizers, non-synthetic fertilizers depend on microbial activity for the slow release of nutrients. Non-synthetic fertilizers also have lower concentrations of nutrients, which means nutrient-deficient soils require larger quantities of fertilizer.
Synthetic fertilizers consist of organic and inorganic materials. Examples include ammonium nitrate, sulfate and urea. Some formulas are called complete or balanced formulas because they contain all three of the main nutrients -- nitrogen, phosphorus and potassium. For example, a 10-20-10 formula contains 10 percent water soluble nitrogen, 20 percent available phosphate and 10 percent potash. Other formulas are called incomplete formulas because they contain a greater concentration of only one nutrient. For instance, a 0-20-0 formula contains a greater concentration of phosphorus. Synthetic materials are manufactured to dissolve in water and make nutrients available to plants quickly. They also draw water out of the plants and cause fertilizer burn.
Slow-release fertilizers, also called timed-release fertilizers, release nutrients to the soil at a predictable rate. Urea formaldehyde serves as an example of a slow-release fertilizer that requires microbes to break down complex nitrogen compounds before any nitrogen becomes available to the plant. Isobutylidene diurea serves as an example of a slow-release fertilizer that contains water insoluble nitrogen that breaks down at temperatures above 75 degrees F. Sulfur-coated urea is a type of slow-release fertilizer that leaches small amounts of nitrogen when the fertilizer pellets are wet.