Ammonium fixation and availability of fixed ammonium In some Dutch loam and clay soils.

Abstract

Samples of loam and clay soils containing young common (Fithian) illite recently reclaimed from Lake IJssel and samples of old river clays (fertilized with 0, 250, 450, 650 and 1000 kg/ha/yr of K₂SO₄) and containing old open (Ammersooite) illite were treated with 100 ppm N applied as (NH₄)₂SO₄ to determine ammonium fixation, the effect of K on ammonium fixation and the availability of fixed ammonium to nitrifying bacteria. The young polder soils fixed 3-10% of the added ammonium N and fixation was completed within 24 hours. Old river clay with no history of K fertilization fixed 87 % of the added ammonium-N in 72 hours. In old river clays the total amount of fixed ammonium and the fixation period both decreased as rate of K fertilization increased. None of the ammonium fixed by a young polder soil was nitrified during four months' incubation. 70% of the ammonium fixed by an old river clay was nitrified within two months but no nitrification occurred during a further two months' incubation. The addition of K prevented nitrification of fixed ammonium in old river clay. (Abstract retrieved from CAB Abstracts by CABI’s permission)