Runoff irrigation of crops with contrasting root and shoot development in northern Kenya: water depletion and above- and below-ground biomass production

In a runoff irrigation system using levelled basins, the water uptake patterns of different plant species (Acacia saligna (Labill.) H. L. Wend. and Sorghum bicolor (L.) Moench.) with contrasting root and shoot development were compared. Rainfall amounts during 1995 led to enough runoff water for realizing two cropping cycles. The amount of irrigation water was sufficient to fill the moisture-depleted zone in the upper 1·5 m to field capacity. The total above-ground biomass production of sorghum equalled the biomass production of Acacia during the cropping season. Soil water depletion was higher in soils cropped with Acacia and showed a different spatial and temporal pattern than the annual crop. Total root length density of sorghum was two times higher than that of Acacia, but the root system of sorghum was shallower than the tree root system. Water uptake patterns are discussed with respect to the contrasting aboveand below-ground growth strategies of the two plant species.