Ariane Krause, Thomas Nehls, Eckard George, Martin Kaupenjohann:
Field Experiment on a Tropical Andosol in Karagwe, Tanzania Using Organic Wastes from Bioenergy Provision and Ecological Sanitation

ARIANE KRAUSE, THOMAS NEHLS, ECKARD GEORGE, MARTIN KAUPENJOHANN
$^{1}$Technische Universität Berlin, Postgraduate Program Microenergy Systems at Center for Technology and Society, Germany
$^{2}$Technische Universität Berlin, Dept. of Soil Conservation, Germany
$^{3}$Institute of Vegetable and Ornamental Crops (IGZ), Germany
$^{4}$Technische Universität Berlin, Dept. of Soil Science, Germany

Because of high phosphorus (P) fixation, Andosols regularly require P amendments to guarantee high crop production and sustainable land use. Further they tend to accumulate organic carbon (C) and thus they can act as CO₂ sinks for C-sequestration. Ecological sanitation and bioenergy production, such as anaerobic digestion and pyrolysis or microgasification, can contribute to local nutrient and carbon recycling. Soils can be amended with compost, urine, biogas slurry or CaSa-compost (containing biochar and sanitised human excreta) to replenish nutrients and to guarantee sustainable crop production. A practice-oriented field experiment was conducted to assess five amendments' short term effects on crop productivity, plant nutrition and soil properties on tropical Andosol in Karagwe, Tanzania. Seven intercropped local plant species were planted on 9 m² plots with five repetitions arranged in a latin rectangle. Differences in biomass production were related to the availability of water and nutrients in the soil. The amendments did not change the plant-available water in the soil significantly. Therefore, differences in crop yield and plant nutrition could be related to nutrient availabilities from the soil alone. Biogas slurry, compost and CaSa-compost increased the aboveground biomass of Zea mays by about 140, 154 and 211% respectively as compared to the unfertilised control treatment. Plots amended with biogas slurry, compost and CaSa-compost yielded about 2,630, 3,180 and 4,400kgha^-1 air-dry maize grains respectively compared to 1,100kgha^-1 on the control plots. Nutrient balancing revealed that 20 % of the applied P was taken up by plants. Only the amendment of CaSa-compost significantly increased plant-available P concentrations (from 0.5 to 4.4mgkg^-1) in the top-soil compared to the untreated control. We conclude that the used amendments are applicable and effective to sustain fertility and productivity of the local Andosol. Especially CaSa-compost contributes to mitigating P-scarcity and acidification.

Keywords: Biogas slurry, composted biochar, crop nutrition, ecological sanitation, field experiment, hydraulic properties, soil chemistry, soil improvement, Terra Preta practice, waste as resource

Footnotes

...P

Contact Address: Ariane Krause, Technische Universität Berlin, Postgraduate Program Microenergy Systems at Center for Technology and Society Sec. Hbs 1; Hardenbergstr. 16-18, 10623 Berlin, Germany, e-mail: krauseztg.tu-berlin.de