Zeller


Die Bodenkultur - Journal for Land Management, Food and Environment

V. Zeller, E. Kandeler and V. Trockner:

Measurement of net nitrogen mineralization in grassland - a comparison of methods

Summary

Three in situ methods to measure net nitrogen mineralization (NNM) were compared. The NNM (0-20 cm) was measured after plant removal as accumulated ammonium and nitrate N according to the following methods:

a) in open cores with an anion exchange resin layer (resin core method),

b) in closed polyethylene hags (buried bag method) and

c) in covered fallow plots.

For the resin core method, the influence of exposure time on the NNM, as well as changes in water content and microbial biomass N during the exposure were investigated. In the fallow plots, either nitrate leaching, denitrification or microbial immobilization led to unreliable results. Compared to the resin core method, the buried bag method showed higher NNM values. The resin core method gave similar results for exposure times of 3 and 6 weeks. Compared with the undisturbed soil, the water content in cores after 6 weeks of exposure was higher in dry grassland, whereas the microbial biomass N remained constant. In contrast, the irrigated plot showed no differences in water content, but a biomass N loss of about 26-45 %. For further in situ measurements of NNM the use of the resin core method is recommended with exposure times of 6 weeks. Changes in water content and microbial biomass should be determined as well.

Key words:  Buried bag method, grassland, microbial biomass N, net nitrogen mineralization, resin core method.