Tropentag, September 17 - 19, 2014 in Prague, Czech Republic "Bridging the gap between increasing knowledge and decreasing resources"

Impact of “Biological Nitrification Inhibition” on N Recovery Efficiency, N Leaching and N₂O Emissions Using the Example of Brachiaria humidicola

¹University of Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics, Germany
²International Center For Tropical Agriculture (CIAT), Colombia

Abstract

Biological Nitrification Inhibition (BNI) has been reported for several plant species. Amongst these the tropical forage grass Brachiaria humidicola has gained major attention due to its high BNI-activity. An increased N-recovery efficiency (reduced N-leaching) and reduced N₂O-emissions are proposed for B. humidicola based pastures.
Breeding programs targeting on BNI-activity currently lack indicators suitable for large scale field evaluation. A promising approach could be the link between the plant ¹⁵N-signature and its N-nutrition (ammonium versus nitrate). As both pools usually possess different isotopic signatures, the nutritional contribution of each N-pool should be reflected in the plant, thus indicating the magnitude of nitrification inhibition (BNI-activity).
Objectives of the present study are the evaluation of selected B. humidicola-hybrids regarding their BNI-activity; the assessment of BNI's impact on N recovery efficiency, N-leaching and N₂O-emissions; and a correlation analysis on the relation between the plant's BNI-activity and its ¹⁵N-signature.
The study was designed as a two phased greenhouse trial. In a first phase the plant ¹⁵N-signatures were analysed and assessed in relation to the ¹⁵N background signal of soil and fertiliser. In a second phase the fertilisation regime was switched to ¹⁵N-labeled ammonium sulfate. This enabled tracing of N-fluxes, estimation of the hybrid's BNI-activity (via the nitrification rates) and determination of overall N recovery efficiency. N-leaching and N2O-emissions were assessed in relation to the estimated BNI-activity.
Plants were cultivated in PVC-tubes (Ø12cm * 100cm) on a ferralitic substrate. Nitrification rates and nitrate dislocation were derived on the basis of soil nitrate levels determined by regular sampling of soil solution through suction tubes installed at different depths within the soil column. Anion exchange resin bags were installed at the bottom of the column to quantify cumulative N-leaching. N₂O-emissions were quantified after irrigation inducing reducing conditions.

Keywords: Brachiaria, denitrification, N use efficiency, N₂O emissions, nitrification, nitrification inhibition

Contact Address: Konrad Egenolf, University of Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics, Neuhauser Straße 23, 70599  Plieningen, Germany, e-mail: konrad.egenolfuni-hohenheim.de