ALBERT

Description: Andosols require the regular application of phosphorus (P) to sustain crop productivity. In a practice oriented field experiment at an Andosol site in NW Tanzania, the effects of various soil amendments (standard compost, urine, biogas slurry and CaSa-compost [biochar and sanitized human excreta]) on (i) the productivity of locally grown crop species, on (ii) the plants' nutrient status and on (iii) the soil's physico-chemical properties were studied. None of the amendments had any significant effect on soil moisture, so the observed variation in crop yield and plant nutrition reflected differences in nutrient availability. The application of CaSa-compost increased the level of available P in the top-soil from 0.5 to 4.4 mg kg−1 and the soil pH from 5.3 to 5.9. Treatment with biogas slurry, standard compost and CaSa-compost increased the above-ground 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 especially effective in mitigating P deficiency and soil acidification. We conclude that all treatments are viable as substitute for synthetic fertilizers. However, 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 loop can be closed.