Tree and crop fine root distribution and belowground competition as affected by a climatic gradient in agroforestry parkland systems in Burkina Faso (West Africa)

This research assessed precipitation increase along a climactic gradient effect on tree and crop root length densities and belowground competition in parklands systems of Vitellaria paradoxa C. F Gaertn, Parkia biglobosa (Jacq.) Benth with Sorghum bicolor (L.) Moench for formulating parklands management options improving crop productivity. Field experiments were conducted at three sites along an increasing rainfall gradient. Soil samples were taken, roots were washed and sorted by categories and root length density was estimated using the method of Tennant. Belowground competition was assessed using the ratio method. Correlation between crop root and aboveground biomass was tested. For topsoil, higher crop root length density was at Sokouraba (0.087 ± 0.007 cm.cm -3 ). For subsoil, crop and tree average root length density was higher at Tougouri and were respectively 0.05 ± 0.009 and 0.117 ± 0.021 cm.cm -3 . Trees reduce crop root length density with precipitation increase and more under P. biglobosa. Belowground competition along a climatic gradient and its interaction with zones and tree species was not significantly different. Higher crop root length density obtained at topsoil with precipitation increase did not reduce belowground competition. Tree management options reducing tree roots should be tested on belowground competition along a climatic gradient. Key words : precipitation increase, management options, root length.