Non-exchangeable NH4-N in the subsoil:Significance for the N nutrition of plants (NitroNex)

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The project is dealing with the contribution of non-exchangeable NH4-N in the subsoil for the N nutrition of plants. It is divided into two main parts: In part 1 the content of nonexchangeable NH4-N in the subsoil of the Central field experiment (CeFiT) under different crops and influencing factors will be investigated. Special consideration will be given to the drilosphere, where easily mineralizable organic material is translocated into deeper soil layers and NH4+-ions, formed after mineralization may be specifically bound in interlayers of 2:1 clay minerals in the vicinity of biopores. Furthermore attention will be given to the reduction of NO3-, translocated into the subsoil, to NH4+ as a source for NH4+-fixation. In part 2 the amounts of non-exchangeable NH4-N released from subsoils throughout the growing season will be quantified. Special attention will be given to the influence of the root system on the mobilization of NH4+-ions from the interlayers of clay minerals. Partially interlayers of clay minerals will be labelled with 15NH4+. Under field conditions, in the Central microcosm experiment (CeMiX) as well as in model experiments with special containers, that allow to take soil samples from defined distances from the root system, depletion curves of nonexchangeable NH4-N will be created.