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Biochar as a boon for soil fertility in the tropics still has to show that it is able to provide the same benefits to soils in temperate regions. Here an Austrian study with the objective to analyze the extent of benefits that biochar application offers to agricultural soils in Europe beyond its role as a carbon sequestration strategy is presented. Based on hypothesis testing, several potential benefits of biochar were examined in a series of lab analyses, greenhouse and field experiments. Three hypotheses could be confirmed: biochar can protect groundwater by reducing the nitrate migration in seepage water; biochar can mitigate atmospheric greenhouse gas accumulation by reducing soil N2O emissions; and biochar can improve soil physical properties by increasing water storage capacity. One hypothesis was only partly confirmed: biochar supports the thriving of soil microorganisms only in specific soil and climate settings. Two hypotheses were refuted: biochar does not generally provide nutrients to plants except when produced from specific feedstocks or by combining it with mineral or organic fertilizers; the cost-effectiveness of biochar application is not given under current production costs if the existing benefits of biochar are not transferable to financial value.
Nitrogen cycling in terrestrial ecosystems is complex and includes microbial processes such as mineralization, nitrification and denitrification, plant physiological processes (e.g. nitrogen uptake and assimilation) and physicochemical processes (leaching, volatilization). In order to understand the challenges nitrogen puts to the environment, a thorough understanding of all these processes is needed.
This chapter provides an overview about processes relating to ecosystem nitrogen input and output and turnover. On the basis of examples and literature reviews, current knowledge on the effects of nitrogen on ecosystem functions is summarized, including plant and microbial processes, nitrate leaching and trace gas emissions.
Key findings/state of knowledge
Nitrogen cycling and nitrogen stocks in terrestrial ecosystems significantly differ between different ecosystem types (arable, grassland, shrubland, forests).
Nitrogen stocks of managed systems are increased by fertilization and N retention processes are negatively affected.
It is also obvious that nitrogen processes in natural and semi-natural ecosystems have already been affected by atmospheric Nr input.
Following perturbations of the N cycle, terrestrial ecosystems are increasingly losing N via nitrate leaching and gaseous losses (N2O, NO, N2 and in agricultural systems also NH3) to the environment.
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