Pflanzlich-tierische Stoffflüsse und Produktionseffizienzen in der urbanen und peri-urbanen Landwirtschaft einer westafrikanischen Stadt
Zusammenfassung der Projektergebnisse
Urban and peri-urban agriculture (UPA) is increasingly important to secure the livelihoods of urban populations in Sudano-Sahelian West Africa. However, until now little was known about matter fluxes as indicators of bio-physical sustainability in UPA’s plant and animal production systems or negative externalities such as N leaching and volatilisation as well as food contamination, particularly when using untreated municipal wastes and sewage as inputs to crop production. Taking Niamey (Niger, West Africa) as a case study, we determined large annual surpluses of C, N, P and K in vegetable gardens of high and low intensity. In high input millet fields, annual surpluses were only a fraction of those in vegetable gardens, and deficits of -3 kg P and -3 kg K were determined for low input fields. In vegetable gardens, mineral fertilizers accounted for 34 - 48% of N, 15 - 80% of P and 2 - 12% of K inputs. Animal manure contributed 69 - 79% to the C input, 44 - 68% to N, 61 - 73% to P and 48 - 75% to K. In millet fields, manure contributed 13 - 76% of N, 79 - 91% of P and 17 - 65% of K inputs. Mean annual gaseous N emissions (NH3-N and N2O-N) from soils of two gardens using river water for irrigation reached 53 and 48 kg N ha-1 yr-1, respectively, while 25 and 20 Mg C ha-1 yr-1 was lost as CO2-C. Under sewage water irrigation N2O was the main contributor to N losses (68%) which together with NH3 reached 92 kg N ha-1 yr-1 and CO2-C emissions amounted to 26 Mg ha-1 yr-1. 28% of total gaseous C emissions and 30 - 40% of N emissions occurred during the hot dry season from March to May and another 20 - 25% and 10 - 20% during the early rainy season from June to July. Nitrogen and P leaching was remarkably small, partly reflecting extraordinarily low rainfall in the year of measurement. Counts of colony forming units (CFU) of Salmonella spp. and Escherichia coli indicated above threshold contamination levels of 7.2 x 104 CFU 25 g-1 and 3.9 x 104 CFU g-1 in fresh matter of lettuce irrigated with river water and fertilized with animal manure. Salmonella counts averaged 9.8 x 104 CFU 25 g-1 and E. coli counts 0.6 x 104 CFU g-1 for lettuce irrigated with wastewater, while such pathogens were absent on vegetables irrigated with pond water. Overall, vegetable and millet production in Niamey are characterized by poor nutrient use and management, leading to large surpluses of N, P and K in vegetable gardens of low and high input intensity, while C balances remain critical and require recycling of manure to maintain soil C levels. This suggests scope for improved nutrient use efficiency and management in Niamey’s UPA systems such as split application of mineral N and coverage of compost heaps with simple plastic roofs to decrease C and N losses. At the household level nutrient balances (mg kg0.75 d-1) in high-input (HI) sheep/goat enterprises were with 11760 mg N, 1130 mg P, and 11360 mg K much higher than those in low-input (LI) units (170 mg N, 300 mg P, and 120 mg K). In HI cattle enterprises, daily balances were substantially smaller. All animal production systems were characterized by poor conversion efficiencies of offered feed dry matter (13.5 to 46.1 kg kg-1 LWG in cattle and 15.7 to 43.4 kg kg-1 LWG in sheep/goats). Live weight gain (LWG) in HI sheep/goats was 53 g d-1 in the rainy season, 86 g d-1 in the hot dry season and 104 g d-1 in the cool dry season, while HI cattle lost 79 g d-1 in the hot dry season and gained 121 g d-1 and 92 g d-1 in the cool dry and rainy season, respectively. The oversupply of nutrients to cattle and small ruminants in Niamey’s livestock enterprises seems to reflect poor feeding management such as group feeding of animals irrespective of age and physiological status, and the use of inappropriate troughs. The low feed conversion and large positive nutrient balances along with the low growth performance of ruminants and the quasi-absent milk extraction underline the need of improved feeding. For animals that are grazing at the city fringes during daytime, a reduction of the amount of feed offered at the homestead, especially during periods of high feed availability on pastures (cool dry season) is recommended. This would allow to convert more feed nutrients into LWG and milk and less to the dung heap, be it by excretion of faeces and urine or by feed spillage and conversion into litter. Scenario analyses based on modelling work indicated considerable potential for UPA smallholder farmers in Niamey to improve their food security and incomes through goal-oriented livestock nutrition at the farm scale. Together with improved manure handling and storage such practices could increase the value of manure for the production of vegetables and staples, and at the same time contribute to reducing the risks of environmental pollution. The analytical methods and results from this study formed the basis for a series of comparative PhD and post-doctoral studies in Mali, Burkina Faso and Nigeria as well as in Sudan, Afghanistan, Pakistan and India funded by the Volkswagen Foundation, the Alexander von Humboldt Foundation, and the German Academic Exchange Service (DAAD).
Projektbezogene Publikationen (Auswahl)
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2009. Determinants of sustainability in urban and peri-urban agriculture. In Brown, P. et al. (Eds.). Proceedings of the International Plant Nutrition Colloquium, University of California, Davis, USA
Buerkert, A., Schlecht, E., Predotova, M., Diogo, R.V.C., Kehlenbeck, K. and Gebauer, J.
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2010. Emissions of ammonia, nitrous oxide and carbon dioxide from urban gardens in Niamey, Niger. Field Crops Research 115, 1-8
Predotova, M., Gebauer, J., Schlecht, E. and Buerkert, A.
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2010. Horizontal nutrient fluxes and food safety in urban and peri-urban vegetable and millet cultivation of Niamey, Niger. Nutrient Cycling in Agroecosystems 87(1), 81-102
Diogo, R.V.A., Buerkert, A. and Schlecht, E.
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2010. Mineral nitrogen and phosphorus leaching in vegetable gardens of Niamey, Niger. Journal of Plant Nutrition and Soil Science
Predotova, M., Bischoff, W.-A. and Buerkert, A.
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2010. Nitrogen and carbon losses from dung storage in urban gardens of Niamey, Niger. Nutrient Cycling in Agroecosystems 87(1), 103-114
Predotova, M., Schlecht, E. and Buerkert, A.
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2010. Resource use efficiency in urban and peri-urban livestock enterprises of Niamey, Niger. Animal 4(10), 1725-1738
Diogo, R.V.A., Buerkert, A. and Schlecht, E.
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2011. Effects of cuvette surface material on ammonia, nitrous oxide, carbon dioxide and methane concentration measurements.
Journal of Plant Nutrition and Soil Science, Vol. 174. 2011, Issue 3, pp. 347–349.
Predotova, M., Kretschmann R., Gebauer, J. and Buerkert, A.
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Economic benefit of gardeners and retailers from cultivating and marketing of vegetables in Niamey, Niger. Outlook on Agriculture, Vol. 40. 2011, Number 1, pp. 71-78.
Diogo, R.V.A., Buerkert, A. and Schlecht, E.
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Analysis of landscape transformation processes in and around four West African cities over the last 50 years. Landscape and Urban Planning, Vol. 105.2012, Issues 1–2, pp. 94–105.
Brinkmann, K., Schumacher, J., Dittrich, A., Kadaoure, I. and Buerkert, A.
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Sorption and desorption characteristics of ion exchange resins to estimate leaching losses in the field. Communications in
Communications in Soil Science and Plant Analysis, Vol. 43.2012, Issue 7, pp.1065-1072.
Siegfried, K., Vazhacharickal, P.J., Predotova, M. and Buerkert, A.
