Influence of pre-crop and root architecture on the mobilization of non-exchangeable NH4+

Abstract

It is well established that non-exchangeable NH4+ is an important N source for plants. However, release from clay minerals only occurs when the NH4+ concentration of the mineral environment declines below a certain level. This may be conditioned by the growing plant. Although root development differs depending on plant species, the influence of root architecture on the mobilization of non-exchangeable NH4+ is still open to question. We found that mobilization of non-exchangeable NH4+ was higher under oilseed rape as compared to barley; oilseed rape even has allorhize and fescue homorhize roots. This observation could be proved by labeling soil samples with 15NH4+, which were incubated in soil holders under oilseed rape and barley. The higher mobilization of non-exchangeable NH4+ by oilseed rape is therefore assumed to be caused by higher release of H+, displacing interlayer NH4+. Although allorhize roots from pre-crops create more stable biopores with an increasing diameter and living roots of the subsequent crop enter these biopores, we could not find an influence of the pre-crop on the mobilization of non-exchangeable NH4+.

Keywords

• ammonium
• fixation
• availability
• roots
• biopores