Long-term net N mineralization potential as an indicator for soil fertility: chances and constraints

Abstract

The soil capacity to supply nitrogen (N) to crops through decomposition of soil organic matter (SOM) is a main indicator for soil fertility. Assessment of a soil net N mineralization potential via long-term laboratory incubations accounts for many of the influencing factors as it integrates the activity of soil micro-organisms and to some extent, the physical accessibility of SOM. A two-pool first-order kinetic equation was used to fit cumulative net N mineralization data from incubations. It allowed the identification of a fast mineralizable N pool, N_fast (N in fresh residues), and a slow mineralizable N pool, N_slow, which mainly consists of humified SOM. Since the latter represents long-term soil N supply and is a mostly inherent soil property, it could be used as an indicator for soil fertility. We will present results from different studies:

• A watershed study (NW-Germany), where reliable pedotransfer functions for site-specific estimates of pool size N_slow were derived.

• A study in the Kalahari region, where the approach helped to understand the relevance of the soil net N mineralization potential for groundwater pollution with nitrate.

• A study aiming to develop an internet-service for field-specific simulations of current net N mineralization (NW-Germany).

Keywords:

• long-term soil N supply
• laboratory incubations
• biological method
• digital soil maps