Tropentag, September 20 - 22, 2017 in Bonn "Future Agriculture: Social-ecological transitions and bio-cultural shifts"

Nutrient Leaching in Urban Agriculture, Effects of Waste Water Irrigation and Biochar Application to a Petroplinthic Cambisol in N-Ghana

¹Ruhr-Universität Bochum, Inst. of Geography, Soil Science and Soil Ecology, Germany
²University of Kassel, Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Germany

Abstract

Urban Agriculture (UA) in developing countries can contribute significantly to food security and diversity. Excessive use of fertilisers, manures and waste water is well documented in the literature. This may lead to high losses of nutrients through leaching especially when irrigation exceeds the demands. Until today very little work was done to measure nutrient leaching, ways to prevent it and consequently increase nutrient use in UA. Biochar (BC) as a soil amendment received considerable attention in recent years for its potential to increase soil carbon stocks, crop yields and reduce nutrient leaching. Since production of BC is inexpensive and does not require sophisticated technology it may be a good strategy to improve soil fertility and reduce nutrient losses.
We tested the effects of biochar and waste water on nutrient losses from soil through leaching with lysimeters on a Petroplinthic Cambisol in an UA field trial in Tamale, Ghana for two years. 32 wick lysimeter were installed in Control (no amendment), Biochar (20 t ha^-1), NAP (fertilisation according to normal agricultural practice) and NAP + Biochar plots. Lysimeter were sampled weekly, when irrigation or rainfall took place and total amount of leachates were recorded. The samples were analysed for NO₃^-N, NH₄-N, PO4-P, basic cations (K, Ca, Mg, Na) and pH.
The data show a reduction of water use efficiency through waste water irrigation, which is likely attributed to soil water repellency and therefor higher conductivity. Furthermore, N loses through NO₃-N leaching were found to amount to 50-100 kg ha^-1 per season when irrigation was appropriate. When plots where over irrigated NO₃-N leaching reached up to 250 kg ha^-1. BC application did not reduce leaching losses of nutrients.

Keywords: Biochar, nutrient leaching, urban agriculture, waste water

Contact Address: Steffen Werner, Ruhr-Universität Bochum, Inst. of Geography, Soil Science and Soil Ecology, Universitätstr. 140, 44801 Bochum, Germany, e-mail: steffen.wernerrub.de