Articles | Volume 2, issue 2
SOIL, 2, 147–162, 2016
SOIL, 2, 147–162, 2016

Original research article 21 Apr 2016

Original research article | 21 Apr 2016

Organic wastes from bioenergy and ecological sanitation as a soil fertility improver: a field experiment in a tropical Andosol

Ariane Krause1,3, Thomas Nehls2, Eckhard George3, and Martin Kaupenjohann4 Ariane Krause et al.
  • 1Postgraduate program “Microenergy Systems”, Center for Technology & Society, Technische Universität (TU) Berlin, Sekr. HBS 1, Hardenbergstr. 16–18, 10623 Berlin, Germany
  • 2Department of Ecology – Soil Protection, TU Berlin, Sekr. BH 8-1, Ernst-Reuter-Platz 1, 10587 Berlin, Germany
  • 3Leibniz Institute of Vegetable and Ornamental Crops (IGZ), Theodor-Echtermeyer-Weg 1, 14979 Großbeeren, Germany
  • 4Department of Ecology – Soil Science, TU Berlin, Sekr. BH 10-1, Ernst-Reuter-Platz 1, 10587 Berlin, Germany

Abstract. Andosols require the regular application of phosphorus (P) to sustain crop productivity. On an Andosol in NW Tanzania, we studied the short-term effects of amending standard compost, biogas slurry and CaSa compost (containing biochar and sanitized human excreta) on (i) the soil's physico-chemical properties, on (ii) biomass growth and crop productivity, and on (iii) the plants' nutrient status. The practice-oriented experiment design included the intercropping of seven locally grown crop species planted on 9 m2 plots with five repetitions arranged as a Latin rectangle. Differences in plant growth (biomass production and crop yield, e.g., of Zea mays) and crop nutrition (total C, N, P, K, Ca, Mg, Zn, etc.) were related to pH, CEC (cation exchange capacity), total C and the availability of nutrients (N, P, K, etc.) and water (water retention characteristics, bulk density, etc.) in the soil. None of the amendments had any significant effect on soil water availability, so the observed variations in crop yield and plant nutrition are attributed to nutrient availability. Applying CaSa compost increased the soil pH from 5.3 to 5.9 and the level of available P from 0.5 to 4.4 mg per kg. Compared to the control, adding biogas slurry, standard compost and CaSa compost increased the aboveground biomass of Zea mays by, respectively, 140, 154 and 211 %. The grain yields of maize on soil treated with biogas slurry, standard compost and CaSa compost were, respectively, 2.63, 3.18 and 4.40 t ha−1, compared to only 1.10 t ha−1 on unamended plots. All treatments enhanced crop productivity and increased the uptake of nutrients into the maize grains. The CaSa compost was most effective in mitigating P deficiency and soil acidification. We conclude that all treatments are viable as a substitute for synthetic fertilizers. Nevertheless, further steps are required to integrate the tested soil amendments into farm-scale nutrient management and to balance the additions and removals of nutrients, so that the cycle can be closed.

Short summary
In a field experiment in Tanzania, we used substrates from local projects as soil amenders for intercropping relevant local crops, aiming to advance the practical application of known principles for smallholder agriculture in SSA, i.e. biochar and biogas application and EcoSan practices. We studied the short-term effects on crop productivity, plant nutrition and soil properties. By mitigating P scarcity and acidification, yields were increased by up to 400 % compared to the control.