Abstract

Open cycles of organic carbon and nutrients cause soil degradation. Procedures such as ecological sanitation (EcoSan), bioenergy and Terra Preta practice (TPP) can contribute to closing nutrient cycles and may, in addition, sequester carbon. This paper introduces three projects in Karagwe, Tanzania, and their applied approach of integrated resource management to capture carbon and nutrients from different waste flows. Substrates derived from these case studies, biogas slurry, compost and CaSa-compost (containing biochar and sanitized human excreta), were assessed for their nutrient content by analysis of the total element composition. Evaluation focused on potential impacts of the tested amendments on the nutrient availability in the soil as well as on the local soil nutrient balance. Results revealed that all substrates show appropriate fertilizing potential compared to literature, especially for phosphorus (P). CaSa-compost was outstanding, with a total P concentration of 1.7 g dm^-3 compared to 0.5 and 0.3 g dm^-3 in compost and biogas slurry respectively. Furthermore, these soil amendments may reduce acidity of the soil, with a calculated liming effect of 3.4, 2.6 and 7.8 kg CaO for each kg of nitrogen added for biogas slurry, compost and CaSa-compost respectively. To offset negative P balances in Karagwe, about 8100, 6000 and 1600 dm³ ha^-1 are required for biogas slurry, compost and CaSa-compost respectively. We conclude that especially CaSa-compost might offer immediate positive effects to crop production and nutrient availability in the soil.

Key words: Ecological sanitation, bioenergy, Terra Preta practice, biochar, biogas slurry, compost, soil amendments, soil improvement, waste as resource.

Abbreviation

Biochar, Charcoal used as soil amendment; BiogaST, Project “Biogas Support for Tanzania”; CaSa, Project “Carbonization and Sanitation”; CaSa-compost, Product of CaSa-project containing composted biochar and sanitized excreta; CHEMA, Community Habitat Environmental Management; CREEC, Center for Research in Energy and Energy Conservation; EcoSan, ecological sanitation; EfCoiTa, Project “Efficient Cooking in Tanzania”; EWB, Engineers Without Borders; IAASTD, International Assessment of Agricultural Knowledge, Science and Technology for  Development; ICP-OES, Inductively coupled plasma optical emission spectrometry; IGZ,      Leibniz Institute of Vegetable and Ornamental Crops; MAVUNO, MAVUNO Project Improvement   for   Community    Relief    and    Services; (“mavuno” meaning “harvest” in Swahili); m.a.s.l., meter above sea level; SOM,     soil organic matter; SSA, Sub-Saharan Africa; TLUD, top-lit up draft; TPP,Terra Preta practice; TU, Technische Universität; UDDT, urine diverting dry toilet; WHO, World Health Organization.