Nutrient Needs & Availability | Oklahoma State University

Crop Nutrient Needs

There are more than 100 chemical elements known today. Only 16 of them have been identified to be essential to plant growth:

Basic Nutrients: C, H, and O mainly supplied by air and water.
Primary Nutrients: N, P, K
Secondary Nutrients: Ca, Mg, S
Micronutrients: Zn, Fe, Cu, Mn, B, Mo, Cl

Soil, water and air can provide part of the nutrient plants need. The rest need to be supplied through other sources. The amount of each nutrient needs to be supplied through commercial fertilizers or animal manure depends on the type of crop, yield goal and soil available nutrient contents. Soil test is the first right step to obtain information of crop nutrient needs. Soil Test Interpretations lists nutrients requirement for common crops grown in Oklahoma.

You can also obtain recommendation by using this interactive program for a particular crop: Soil Test Interpretation and Fertilizer Decision Support.

Nutrient Availability

Nutrients in animal manure cannot be substituted for those in commercial fertilizers on a pound-for-pound basis because not all the nutrients reported on a manure analysis are readily available to a crop in the year of application.

Availability of Nitrogen

Nitrogen in the organic form must be converted (mineralized) into inorganic forms (ammonium and nitrate) before it can be taken up by roots. In general, about 50% of the organic N may become available the year of application. Organic N released during the 2nd and 3rd cropping years after application is usually about 15% and 6% of the original N content, respectively. Nitrogen availability may be higher if the manure is incorporated shortly after application, e.g., 65%. Nitrogen availability varies with the type of manure, read the following publications for more information on different types of manure:

Availability of Phosphorus and Potassium

Nearly all of the P and K in manure are available for plant use the year of application compared with commercial P and K fertilizers. In general, a 90% availability factor is used for K and P in the manure.