Soils - Part 6: Phosphorus and Potassium in the Soil Glossary

anhydrous ammonia

A gaseous material that is compressed and stored as a liquid. At 60oF, a gallon of anhydrous ammonia weighs 5.15 pounds. Due to the fact anhydrous ammonia needs to go through the nitrification process, it is more resistant to losses from the soil by leaching or denitrification because it is converted by bacterial action to the nitrate form more slowly than are other nitrogen sources.


The temporary tying up of inorganic nitrogen by soil microorganisms that are decomposing plant residues. Immobilized nitrogen is unavailable to plants for a time, but eventually becomes available as the decomposition of residues proceeds and populations of microorganisms decline.

labile phosphorus

Intermediate form of phosphorus that is rather weakly adsorbed or bound to various compounds and clay in the soil.


Elements needed in relatively large amounts for plant growth. Macronutrients include carbon, hydrogen, sulfur, nitrogen, phosphorus, potassium, calcium, magnesium, and oxygen.


Element needed in large amounts for plant development; found naturally and in applied fertilizers.

non-labile phosphorus

A slowly available form of phosphorus.

organic matter

Material that contains carbon and is found in the soil. Most soil organic matter comes from previously living organisms.  Temperature and moisture are the two main factors affecting its development.


The measurement of an aqueous solution’s acidity and alkalinity; measured on a scale of 1 to 14. Pure water has a pH of 7.0 and is neutral. Different crops grow best at different pH levels; pH influences herbicide activity and nutrient uptake.


A key element in the complex nucleic acid structure of plants which regulates protein synthesis; important in cell division and development of new tissues.  Next to nitrogen, the most limiting nutrient in Nebraska crop production; naturally found in sufficient amounts in many Nebraska soils.


An essential plant nutrient needed in large amounts.  Postassium is vital to plant nutrient absorption, respiration, transpiration and enzyme activity. The major portion of potassium is contained in minerals such as feldspar and mica, and clays such as montmorillonite, vermiculite and illite.

soil sample

A collection of individual cores from a known area.

soil test

Chemical analysis of soil samples to assess soil nutrient levels and determine how fertilizer use can be improved.