Water and nutrient use efficiency and the vertical leaching losses in urban vegetable cropping systems in Bobo–Dioulasso (Burkina Faso)

This thesis aimed at a comprehensive characterization of water and nutrient use and nutrient leaching losses in vegetable production systems in Bobo Dioulasso (Burkina Faso) in view of contributing to the development of more rational advice regarding water and nutrient management. For this purpose, three treatments were compared: farmer’s normal fertilization practice (T100), a 30% reduction in fertilization rates (T70), and unfertilized plots (T0). Crop yield, irrigation water and fertilizers management practices as well as plant nutrient uptake were closely monitored. In addition, drainage was collected using zero–tension pan lysimeters at 30 cm depth and analyzed for total N, P, and K content. Sites were equipped with weather stations and TDR probes. Furthermore, sites were also equipped with anion/cation exchange resin cartridges for monitoring the leaching of NO3, NH4, PO4, and K. Four vegetable crops were evaluated: tomato, cabbage, carrot and lettuce. As elsewhere in West Africa, vegetable production in Bobo Dioulasso is characterized by high fertilizer inputs. Indeed, 109 to 2,012 kg N, 66 to 450 kg P and 0 to 393 kg K were applied in excess of plant uptake in both gardens. Free drainage occurred mainly during rainy season, although some drainage occurred during the dry season at Kodeni. The high nutrient inputs combined with periods of high drainage resulted in sometimes high rates of NO3 and PO4 leaching, and on the other hand in strong positive nutrient balances in the soil of both sites. Large amounts of NO3 (236 to 990 kg ha–1 year–1) and to a lesser extend PO4 (28 to 75 kg ha–1 year–1) and K (54 to 214 kg K ha–1 year–1) were thus leached every year beyond the rooting depth. Using a simple fertilizer reduction strategy (T70) allowed to significantly increase the PFP of N, P and K by about 20 to 50% at Dogona and 20 to 45% at Kodeni. It also helped reduce both the amount of nutrients leached as well as the nutrients accumulated in the soil. The reduction in leaching losses ranged from 20 to 90% for NO3, 29 to 74% for PO4 and 14 to 39% for K. Given the sometimes excessive application rates for N and P in the two gardens studied here, reducing nutrient application rates by 30% may help reduce the environmental impact of vegetable cropping systems and lower the costs of investment in fertilizers without adverse effect on yields. Special attention should however be paid to maintaining the K balance.(AGRO 3) -- UCL, 201