Gaseous emissions of nitrogen and carbon from urban vegetable gardens in Bobo‐Dioulasso, Burkina Faso

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 (NH 3 ), nitrous oxide (N 2 O) and carbon dioxide (CO 2 ) 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 NH 3 -N ha -1 h -1 , 154 g N 2 O-N ha -1 h -1 , 12 993 g CO 2 -C ha -1 h -1 were recorded for Kodéni and Kuinima. Estimated annual gaseous N (NH 3 -N + N 2 O-N) and C (CO 2 -C + CH 4 -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 NH 3 , 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.

High environmental risk and low yield of urban tomato gardens in Benin

“…The "Tomato scenario" corresponds to the average of six tomato cropping systems from urban gardens in West Africa for which no field emissions data were available. The "Rotation scenario" corresponds to 25 % of the average of four annual rotations from urban gardens in West Africa (Predotova et al 2010(Predotova et al , 2011Lompo et al 2012). Our study shows large surplus comparable to the literature.…”

“…Regarding fertilizers, large quantities of nutrients in the form of chemical fertilizers and livestock manure are applied to urban gardens Sangare et al 2012). Due to low yields, an important part of nutrient input is lost to the environment (Predotova et al 2010(Predotova et al , 2011Lompo et al 2012). Nutrient emissions such as NH 3 , N 2 O, NO 3 , and phosphorus often contribute considerably to the environmental risk associated to urban cropping systems.…”

Effect of Salinity on Soil Respiration and Nitrogen Dynamics

“…Greenhouse gas emissions are the main reasons of global warming, which caused extreme weather disasters happened frequently all over the world in the past 10 years [1,2]. Previous studies have shown that agricultural-source greenhouse gas emissions account for about 14% of the global greenhouse gas emissions caused by human activities.…”

“…Previous studies have shown that agricultural-source greenhouse gas emissions account for about 14% of the global greenhouse gas emissions caused by human activities. Furthermore, the ratio shows an increasing trend and N 2 O (one of the greenhouse gas) released into atmosphere from soil might increase 26% from 2011 to 2020 [2].…”

“…This is because 520 nitrogen mineralization, as one of the most important soil nitrogen processes, is the process by which organic nitrogen is converted to plant-available inorganic forms by soil animals and microorganisms with N 2 O released through nitrification and denitrification [5,6]. Therefore, the process of soil nitrogen mineralization is closely associated with soil nitrogen-supplying capacities, nitrogen loss and greenhouse gas emissions, which has the important ecological meanings to maintain agricultural ecosystem health and protection [2,7]. Meanwhile, soil respiration is another factor of greenhouse gas emissions due to the CO 2 released [8,9].…”