FRACTIONATION OF SOIL ORGANIC NITROGEN BY MEANS OF SUCCESSIVE IIYDROLYSIS

Abstract

This study was conducted with the objective of identifying the main forros by which the organic N occur in ten soils of Rio Grande do Sul-Brazil as determined by two methods of successive hydrolysis. Among the methods the fractions was extracted from soils by applying different acid concentration and hydrolysis periods, to obtain hydrolyzed of IN HC1/3h (H1), 3N HC 1/3h (112), 6N HC1/4h (113) and 6N HCl/20h (I14). For methods differentiation, a second hydrolysis was performed in these hydrolyzed with propionic and perchloric concentrated acids for the estimation of the a-anino-N fraction. The method with only one hydrolysis was inefficient for characterizing the a-amino-N fraction, whereas the method modification proposes by the same authors enhances the extraction of thus fraction with a consequent decrease of the nonidentified-N fraction. A methodological simplification was applied in the foir described hidrolyzate stages with the objective of reducing then to half, obtaining, in this way, only Hl and H2 data, and estimating by equations the total of four stages. This simplification underestimated the values of the N-organic fractions. As a result new equations were adjusted, showing a better estimation of the different fractions. About 63% of the hydrolyzed-N was recovered during the first two stages of the successive hydrolysis (H1 and 112), the remaining being a more recalcitrant fraction present in the last two stages (113 and 114).