Effects of trees and termite nests in agroforestry parklands on preferential water flows : image analysis of soil profiles after rain simulations and dye experiments

Abstract: Water scarcity is a critical problem in semi-arid tropics of Burkina Faso. Agroforestry parklands, a land use where scattered trees are maintained with annual crops, is commonly practiced by farmers in which termite nests are integral components of the system. This study intended to assess the effects of proximity to trees and termite nests in agroforestry parklands on preferential flow in soils using image analysis of soil profiles after rain simulations and dye-tracer experiments. The measurements were conducted in six transects: three corresponding to small openings (20-30 m) and three to large (77-127m) openings. Within each transect in three positions: next to tree, a tree with a termite nest and center. Each vertical soil profile has size of 500 mm width by 500 mm depth. The images were classified in Erdas Imagine 9.3 and preferential flow parameters (absolute slope sum, uniform front depth, total stained area and others) were defined from the dye infiltration pattern to assess the degree of preferential flow in different positions. The results indicated that the degree of preferential flow significantly decreased from trees with as well as without termite nest to the openings. Preferential flow in tree with termite nests was significantly higher than in the openings. Preferential flow under trees without a termite nest did not significantly differ from trees with termite nests and openings with exception of absolute slope. The water inflitrability was not significant with treatment effect and distance to the nearest tree and termite nest, not related to degree of preferential flow. The opening size effect was significant with absolute slope and close to significance with uniform front depth. Maintaining trees and termites nest in the agroforestry parklands can help in improving preferential flow and may enhance groundwater recharge.