Colorimetrie methods for measurement of ammonium, nitrite and nitrate were modified (a) for application to small samples of nitrogen-poor soils, (b) by centrifugation of extracts to avoid contamination from filter papers and (c) to economize on apparatus and reagents. Estimates by modified methods on thirty soils chosen for their large differences in ammonium and nitrate concentrations were close to estimates on larger samples by a standard method. Ammonium nitrate added to five of the soils was recovered satisfactorily.