Fixation and defixation of ammonium in soils: a review

• Published in: Biology and fertility of soils Vol. 47; no. 1; pp. 1 - 14
• Main Authors: Nieder, Rolf, Benbi, Dinesh K., Scherer, Heinrich W.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.01.2011; Springer Nature B.V
• Subjects: Agriculture; Ammonia; Ammonium; Basalt; Biomedical and Life Sciences; clay; clay fraction; Clay minerals; Climatic conditions; fertilizers; granite; Growing season; Life Sciences; Limestone; loess; marshes; Mineral composition; mineral content; nutrient use efficiency; Oxidizing agents; potassium; Review; sand; Sandstone; soil microorganisms; Soil Science & Conservation; Soil texture; Soil types; Soils; texture; N dynamics; Fixed NH; availability to plants and microflora; ); NH; Recently fixed NH; Native NH
• ISSN: 0178-2762; 1432-0789
• DOI: 10.1007/s00374-010-0506-4

Fixed NH 4 + (NH 4 + f ) and fixation and defixation of NH 4 + in soils have been the subject of a number of investigations with conflicting results. The results vary because of differences in methodology, soil type, mineralogical composition, and agro-climatic conditions. Most investigators have determined NH 4 + f using strong oxidizing agents (KOBr or KOH) to remove organic N and the remaining NH 4 + f does not necessarily reflect the fraction that is truly available to plants. The content of native NH 4 + f in different soils is related to parent material, texture, clay content, clay mineral composition, potassium status of the soil and K saturation of the interlayers of 2:1 clay minerals, and moisture conditions. Evaluation of the literature shows that the NH 4 + f -N content amounts to 10–90 mg kg −1 in coarse-textured soils (e.g., diluvial sand, red sandstone, granite), 60–270 mg kg −1 in medium-textured soils (loess, marsh, alluvial sediment, basalt) and 90–460 mg kg −1 in fine-textured soils (limestone, clay stone). Variable results on plant availability of NH 4 + f are mainly due to the fact that some investigators distinguished between native and recently fixed NH 4 + while others did not. Recently fixed NH 4 + is available to plants to a greater degree than the native NH 4 + f , and soil microflora play an important role in the defixation process. The temporal changes in the content of recently fixed NH 4 + suggest that it is actively involved in N dynamics during a crop growth season. The amounts of NH 4 + defixed during a growing season varied greatly within the groups of silty (20–200 kg NH 4 + -N ha −1  30 cm −1 ) as well as clayey (40–188 kg NH 4 + -N ha −1  30 cm −1 ) soils. The pool of recently fixed NH 4 + may therefore be considered in fertilizer management programs for increasing N use efficiency and reducing N losses from soils.