Soil properties and agronomic effects of repeated biochar amendment and fertilization in an urban horticultural system of Burkina Faso
Delphine Manka’abusi, Nongma Armel Zongo, Désiré Jean‐Pascal Lompo, Christoph Steiner, Bernd Marschner, Andreas Buerkert
Abstract
Biochar application can improve soil quality and plant growth, particularly in combination with organic and mineral fertilization. However, data on its effectiveness in intensively managed (fertilized) gardens within the urban and peri-urban (UPA) agriculture of West Africa is sketchy. We, therefore, studied the medium-term effects of repeated biochar produced from agricultural residues, composted faecal amendments (ECOSAN), and inorganic fertilization on small-scale, intensive urban vegetable production in multiple crop rotations over four years. The experiment used a randomized factorial design comprising different soil management and irrigation practices on a Haplic Lixisol in Ouagadougou, Burkina Faso during eight cropping cycles. Biochar amendment resulted in increased soil organic carbon (SOC) on plots under farmers’ practice (cattle manure + urea). Repeated biochar application at 20 t ha −1 increased SOC by 51 %. Mineral fertilization alone decreased SOC by 32 % (from 12.7 to 8.6 g C kg −1 soil) after 6 months with a progressive decline and soil acidification over time. During this period fertilization with ECOSAN at 16–23 t ha −1 per cropping cycle increased yields and soil pH from 6.5 to 7.4. Four years after its application biochar still increased total fresh matter yield of cabbage by 32 % but showed no effect on amaranth while repeated biochar application only increased total fresh matter yields of the first crop after reapplication. Nitrogen use efficiency (NUE) was higher with mineral fertilizer (NPK) and mineral fertilizer in combination with organic fertilizer (FP) than with ECOSAN alone. The study demonstrates effect of biochar on SOC with less pronounced, crop-specific agronomic benefits. • Biochar in the soil for four years maintained soil total carbon. • Biochar increased nitrogen use efficiency after four years of application to farmers’ practice (by up to 35 %). • Combination of organic and mineral N fertilization increased NUE up to 45 %. • Application of ECOSAN (sewage sludge) increased soil pH.