Accurate indexes of the availability to plants of nutrients in soils are needed for comparisons of different chemical tests to determine which tests should be used in the laboratory for any given group of soils. This study was conducted to develop and improve techniques for obtaining such standard indexes of nutrient availability to plants. Emphasis was placed on: (a) treating the soil similarly (or uniformly) before testing in the greenhouse and laboratory and (b) avoiding treatments during the greenhouse cropping that might influence the availability of the soil nutrient being tested.
The greenhouse technique involved growing plants on undried samples of 24 different soils. Water was added directly to the soils during plant growth, but nutrients other than the one being tested were added by a method which minimized contact with the soil.
Hanway, John J. and Ozus, Turgut
"Comparisons of laboratory and greenhouse indexes of nutrient availability in soils,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 35
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol35/iss544/1