Depletion of non-exchangeable NH 4-N in the soil—root interface in relation to clay mineral composition and plant species

Abstract

Experiments were carried out with 10 soils with different clay contents and different clay composition to investigate the dynamics of non-exchangeable NH + 4 and 1 M HCl extractable NH + 4, respectively, in the vicinity of the roots. The experimental plant was rape ( Brassica napus). In addition the influence of plant species on the mobilization of non-exchangeable NH + 4 was investigated with ryegrass ( Lolium multiforum) and red clover ( Trifolium pratense) on a soil with a higher proportion of smectites and vermiculite. The depletion zone of non-exchangeable NH + 4 as well as 1 M HCl extractable NH + 4 extended to about 3 mm from the root zone in soils with a higher proportion of smectites and vermiculite, while in soils with mainly illites the depletion of both N fractions in the root vicinity was negligible. The depletion was less pronounced for red clover. It is suggested that the release of ammonium from the interlayers depends on clay mineral characteristics as well as on plant species.