Soil Fertility

Soil Fertility and Nutrient Management

Soil fertility explains the soil’s ability to supply plants essential nutrients (PEN). Nutrient Management is the practice of applying commercial and organic sources of plant essential nutrients to the soil. There are 16 PEN which are divided into four categories. To be considered a PEN the nutrient must fulfill one of two criteria: 1) in its absence the plant is unable to complete a normal life cycle or 2) the element plays a role in the plant metabolism. Finally PENs cannot be replaced by another element. For example, correcting a Nitrogen deficiency by adding Sodium nor are elements that only impact soil properties, i.e lime or organic matter, considered plant essential. The only method of knowing the nutrient need of the crop is through soil testing.

Oklahoma Soil Fertility and Nutrient Management Facts

  • The most limiting nutrient in Oklahoma crop production is N.
  • For every 1 percent OM there is approximately 1000 lbs of N.
  • Each year 1-2 percent of the OM breaks down releasing nutrients.
  • Banding P and K is the most efficient method of application.
  • In most crops split application of N is the best management practice.
  • Nitrogen use efficiency in cereal crops is about 33 percent.
  • Availability of all nutrients is impacted by soil pH.
  • Some nutrients are supplied to some degree through rainfall and irrigation (N, S, Cl)
  • Applied P is only available for 1 to 1.5 yrs. (exception Large P additions or Alfalfa)
  • There is strong support for good practices available through NRCS.

Why manage nutrients from a land-owner’s point of view?

  • Maximize yields with optimum fertility maximizes return and soil quality.
  • Proper fertility ensures quality product, i.e. grain and forage.
  • Economical losses occur with both over and under application of nutrients.


OSU Soil Testing
International Plant Nutrition 4 Rs
Nutrient Stewardship
Down and Dirty with NPK
Click on the following links to view PDF files.

How to Get a Good Soil Sample
Understanding Your Soil Test Report
OSU Soil Test Interpretations
Procedures Used by OSU Soil, Water, and Forage Analytical Laboratory
Oklahoma Soil Fertility Handbook