Ninhydrin-reactive nitrogen measurements of microbial biomass in 0.5 m K2SO4 soil extracts

✍ Scribed by R.G. Joergensen; P.C. Brookes

• Book ID: 118976588
• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 528 KB
• Volume: 22
• Category: Article
• ISSN: 0038-0717
• DOI: 10.1016/0038-0717(90)90027-w

✦ Synopsis

Amato and Ladd showed that the amount of ninhydrin-reactive nitrogen (ninhydrin-N) extracted from soil by 2 M KCI following CHCI, fumigation is a reliable and sensitive indicator of the amount of soil microbial biomass. However, when we attempted the assay in 0.5 M K,SO, soil extracts, serious analytical problems (e.g. precipitation of CaSO, and KrSO,) occurred. which invalidated the ninhydrin-N determinations. As measurement of biomass C (and probably biomass N) in soils by fumigation-extraction is more reliable when KrSO,. rather than KCI, is used as the extractant, we modified the ninhydrin-N assay procedure to permit measurements in 0.5~ K,SO,. Our modified procedure is described. A strong relationship (r = 0.99) between ninhydrin-N measured in KCI and KrSO, soil extracts was obtained (KCI-ninhydrin-N = 0.90 K,SO,-ninhydrin-N). There were also strong linear relationships (r = 0.91-95) between biomass C, biomass N and biomass ninhydrin-N (all extracted with 0.5 M K,SO,). We conclude that reliable ninhydrin-N measurements are obtained in 0.5 M K,SO, soil extracts by our modified procedure. lNTRODUCXlON