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Competency Area 4: Nutrient Sources, Analyses, Application Methods

PO 30. Define the following commercial fertilizer terms.

  1. Nutrient use efficiency
  2. Total availability
  3. Water solubility
  4. Guaranteed analysis
  5. Salt effect

Nutrient use efficiency is the yield output per unit input (e.g. bushels of corn per lb of applied N).

Total availability is the total amount of a nutrient that is eventually expected to become plant available.  It should be noted that this could be extended over many years.

Water solubility reflects the portion of the fertilizer that dissolves in water (and is thus more immediately available).

Guaranteed analysis is the minimum amount of N, P2O5, K2O, etc. in the fertilizer material.  The Association of American Plant Food Control Officials (AAPFCO) writes rules, definitions, and labeling standards for fertilizer industry.  States then have laws for guaranteed analysis, sales and distribution.  In New York, see Section 10 of Ag and Markets Law.

The salt effect of a fertilizer reflects the amount of soluble salts in the soil solution, in direct contact with roots.  High soluble salt content (which can result from high applications of N as ammonium salts, K sources, etc.) can cause seedling damage through dehydration.