In view of the fact that no data had ever been obtained on the quantitative relationships of the organic material in the soil by such methods as would preclude a chemical transformation, two things seemed desirable, in continuing the humus investigations at the Iowa Agricultural Experiment Station. First, to attempt the analysis of the organic material of the soil without subjecting it to hydrolysis or other chemical change, and second, to correlate the proportionate quantities of the compounds or classes of compounds found with the kind of soil, its history, treatment, fertility, etc.
Potter, R. S. and Snyder, R. S.
"Determination of amino acids and nitrates in soils: amino acids, ammonia and nitrates in manured and limed soil,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 2
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol2/iss24/1