Nitrogen—Total

The determination of total nitrogen (N) in soils and other complex heterogeneous materials containing several forms of N presents many difficulties. Total N analysis of soils is further complicated by the inadequacy of knowledge concerning the forms of N present and by the low N content of the material under analysis. The Kjeldahl procedures generally employed for determination of total N involve two steps: digestion of the sample to convert organic N to NH4 +-N and determination of NH4 +-N in the digest. Soil samples to be analyzed for total N are usually dried, ground, and sieved before analysis, and they are often stored for analysis in paper bags or other containers that are not airtight. Although various methods have been proposed for direct determination of NH4 + in Kjeldahl digests, this determination is usually performed by estimation of the NH3 liberated by distillation of the digest with strong alkali.