Tropentag, September 19 - 21, 2016 in Vienna, Austria "Solidarity in a competing world - fair use of resources"

Brachiaria humidicola Grass Reduces Soil Nitrous Oxide Emissions from Bovine Urine Patches under Tropical Conditions

¹International Center for Tropical Agriculture (CIAT), Colombia
²University of California, Dept. of Land, Air and Water Resources, United States of America
³INTA EEA, Argentina

Abstract

The generally high levels of nitrogen (N) in bovine urine result in the formation of soil nitrous oxide (N₂O) emission hotpots when bovine urine is deposited in grazed pastures. High spatial variability in the distribution of urine patches makes mitigation of N₂O emission challenging. Previous studies have reported that the roots of tropical forages such as Brachiaria humidicola (Bh) exude organic molecules that can inhibit the activity of soil microbial nitrifiers (biological nitrification inhibition-BNI), thus reducing ammonia oxidation and, consequently, nitrate and N₂O production. We hypothesised that N₂O emissions from soils under forages with BNI capacity are lower than from soils under forage species without BNI capacity. To test this hypothesis, field plots with two forage cultivars, Brachiaria Hybrid Mulato (BHM) and Bh 679 which, correspondingly, have low and high BNI capacity, were selected from a long-term field experiment (10 years) at the International Center for Tropical Agriculture in Colombia. Soil nitrification rates and denitrification potential were evaluated through laboratory assays conducted using soils from the selected field plots. Soil N₂O emissions from simulated urine and water patches were monitored using the static chamber technique over a 30 day period. Concurrently, soil variables such as mineral N and moisture were monitored. Results from the laboratory assays show a suppression of both nitrification and denitrification in soils from plots with Bh 679 than those BHM. Cumulative N₂O fluxes were higher from soils under BHM (155 mg N₂O-N per m²) compared to those under Bh 679 (60 mg N₂O-N per m²). N₂O emissions were not related to N input. We conclude that tropical forages with BNI capacity can play a key role in mitigating N₂O emissions from bovine urine deposited on grazing pastures.

Keywords: Biological nitrification inhibition, climatic change mitigation, denitrification, nitrification, nitrous oxide, urine patches

Contact Address: Jacobo Arango, International Center for Tropical Agriculture (CIAT), Tropical Forages, A A 6713, NA Cali, Colombia, e-mail: j.arangocgiar.org