Die Bodenkultur - Journal for Land Management, Food and Environment

G. Dersch, M. Pfeffer und O. H. Danneberg:

Determination of the N mineralization potential of different soils by anaerobic incubation as calibrated in a pot-experiment


In a pot experiment with Italian raygrass as testplant and at optimal conditions for N mineralization from the organic N pool (adequate water supply, no relevant mineral N content in the soil/sand substrate) about 70 % of the N uptake variation from the above ground grass vegetation could be explained by the biological parameter “anaerobic incubation from dried soil samples“. Thereby a method is available now, which renders a more accurate quantification of the N mineralization potential of soils compared with humus or total N content.

Since the different soil types behave similarly, there is no need for differentiation in the interpretation of the anaerobic incubation result on arable land with conventional tillage treatment. A restriction should be stressed for sites with higher humus (> 6 %) and total N content (> 0,6 %), as then the actual net N mineralization may be underestimated.

The anaerobic incubation is conducted within the ordinary course of soil testing on air dried samples. Due to this soil pretreatment these values exceed the results obtained from original moist samples, but a strong correlation exists between both soil pretreatment procedures. To some extent the higher values may be caused by the lysis of microbial cells during soil drying.

Without N fertilization the N mineralization potential as indicated by the incubation method is reduced within one vegetative period. Therefore it is assumed, that N fertilizer recommendations based on these results may not be adjustable for a period of about six years as it is possible for P and K soil tests.

These results strongly confirm the present interpretation of anaerobic incubation: At low levels in general a small 10% increase of the usual N fertilizer rate is recommended, at high levels reductions between 15 and 50 % of the normal N dose depending on the particular N uptake pattern of the crops is intended.

Key words: N mineralization potential, N fertilization, anaerobic incubation, soil types, pot experiment.