Abstract
In large areas of sub-Saharan Africa crop production must cope with low soil fertility. To increase soil fertility, the application of biochar (charred biomass) has been suggested. In urban areas, untreated waste water is widely used for irrigation because it is a nutrient-rich year-round water source. Uncertainty exists regarding the interactions between soil properties, biochar, waste water and fertilization over time. The aims of this study were to determine these interactions in two typical sandy, soil organic carbon (SOC) and nutrient depleted soils under urban vegetable production in Tamale (Ghana) and Ouagadougou (Burkina Faso) over two years. The addition of biochar at 2 kg m−2 made from rice husks and corn cobs initially doubled SOC stocks but SOC losses of 35% occurred thereafter. Both biochar types had no effect on soil pH, phosphorous availability and effective cation exchange capacity (CEC) but rice husk biochar retained nitrogen (N). Irrigation with domestic waste water increased soil pH and exchangeable sodium over time. Inorganic fertilization alone acidified soils, increased available phosphorous and decreased base saturation. Organic fertilization increased SOC, N and CEC. The results from both locations demonstrate that the effects of biochar and waste water were less pronounced than reported elsewhere.
Highlights
In large areas of sub-Saharan Africa crop production must cope with low soil fertility
Crop production in sub-Sahara Africa must cope with low and erratic rainfall and low soil fertility caused by low soil organic carbon (SOC) contents, low cation exchange capacity (CEC), low water holding capacity and a labile soil structure[1,2]
Half a year after biochar addition, lower SOC stocks were measured at both sites, indicating a SOC loss in BC plots of 27 ± 13% in Tamale and of 35 ± 5% in Ouagadougou
Summary
In large areas of sub-Saharan Africa crop production must cope with low soil fertility. In view of the above, the aims of this field study were to determine the effects of biochar additions, fertilization as well as irrigation water quality and quantity on soil properties under typical urban vegetable production in Tamale (Northern Ghana) and Ouagadougou (Central Burkina Faso). To this end, the study reports results from five soil sampling campaigns carried out on two multi-factorial field experiments over a time period of two years
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