Castaldi et al. 2013. Nitrous oxide emissions from soil of an African rain forest in Ghana

Castaldi, S., Bertolini, T., Valente, A., Chiti, T., and Valentini, R.:2013. Nitrous oxide emissions from soil of an African rain forest in Ghana, Biogeosciences, 10, 4179-4187

Abstract
Recent atmospheric studies have evidenced the imprint of large N₂O sources in tropical/subtropical lands. This source might be attributed to agricultural areas as well as to natural humid ecosystems. The uncertainty related to both sources is very high, due to the scarcity of data and low frequency of sampling in tropical studies, especially for the African continent. The principal objective of this work was to quantify the annual budget of N₂O emissions in an African tropical rain forest. Soil N₂O emissions were measured over 19 months in Ghana, National Park of Ankasa, in uphill and downhill areas, for a total of 119 days of observation. The calculated annual average emission was 2.33 ± 0.20 kg N-N₂O ha⁻¹ yr⁻¹, taking into account the proportion of uphill vs. downhill areas, the latter being characterized by lower N₂O emissions. N₂O fluxes peaked between June and August and were significantly correlated with soil respiration on a daily and monthly basis. No clear correlation was found in the uphill area between N₂O fluxes and soil water content or rain, whereas in the downhill area soil water content concurred with soil respiration in determining N₂O flux variability. The N₂O source strength calculated in this study is very close to those reported for the other two available studies in African rain forests and to the estimated mean derived from worldwide studies in humid tropical forests (2.81 ± 2.02 kg N-N₂O ha⁻¹ yr⁻¹).

Lompo et al. 2012. Gaseous emissions of nitrogen and carbon from urban vegetable gardens in Bobo-Dioulasso, Burkina Faso. Journal of Plant Nutrition and Soil Science 175, 846-853

Lompo, D.J.-P., Sangaré, S.A.K., Compaoré, E., Papoada Sedogo, M., Predotova, M., Schlecht, E., Buerkert, A., 2012. Gaseous emissions of nitrogen and carbon from urban vegetable gardens in Bobo-Dioulasso, Burkina Faso. Journal of Plant Nutrition and Soil Science 175, 846-853 

 

Abstract

Urban and peri-urban agriculture (UPA) is an important livelihood strategy for the urban poor in sub-Saharan Africa and contributes to meeting increasing food demands in the rapidly growing cities. Although in recent years many research activities have been geared towards enhancing the productivity of this land-use system, little is known about turnover processes and nutrient efficiency of UPA. The aim of our study therefore was to determine horizontal fluxes of N, P, K, and C as well as gaseous N and C emissions in urban vegetable gardens of Bobo-Dioulasso, Burkina Faso. Two gardens referred to as “Kodéni” and “Kuinima” were selected as representative for urban and peri-urban systems classified as: (1) “commercial gardening + field crops and livestock system” and (2) “commercial gardening and semicommercial field crop system”, respectively. A nutrient-balance approach was used to monitor matter fluxes from March 2008 to March 2009 in both gardens. Ammonia (NH₃), nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from the respective soils were measured during the coolest and the hottest period of the day using a closed-chamber system. Annual partial balances amounted to 2056 kg N ha^–1, 615 kg P ha^–1, 1864 kg K ha^–1, and 33 893 kg C ha^–1 at Kodéni and to 1752 kg N ha^–1, 446 kg P ha^–1, 1643 kg K ha^–1, and 21 021 kg C ha^–1 at Kuinima. Emission rates were highest during the hot midday hours with peaks after fertilizer applications when fluxes of up to 1140 g NH₃-N ha^–1 h^–1, 154 g N₂O-N ha^–1 h^–1, 12 993 g CO₂-C ha^–1 h^–1 were recorded for Kodéni and Kuinima. Estimated annual gaseous N (NH₃-N + N₂O-N) and C (CO₂-C + CH₄-C) losses reached 419 kg N ha^–1 and 35 862 kg C ha^–1 at Kodéni and 347 kg N ha^–1 and 22 364 kg C ha^–1 at Kuinima. For both gardens, this represented 20% and 106% of the N and C surpluses, respectively. Emissions of NH₃, largely emitted after surface application of manure and mineral fertilizers, accounted for 73% and 77% of total estimated N losses for Kodéni and Kuinima. To mitigate N losses nutrient-management practices in UPA vegetable production of Bobo-Dioulasso would greatly benefit from better synchronizing nutrient-input rates with crop demands.