Water availability and soil suitability for irrigation water impoundments in the federal district of Brazil

The main reasons are the poor soil fertility and the high aluminum toxicity of the soils, restricting the rooting depth of many crops. Shallow rooting is responsible for the occurrence of serious soil-water stress conditions, even in the wet season. One of the alternatives for minimizing the adverse effects of droughts is supplemental irrigation. This thesis deals with a limited number of aspects related to the supplemental irrigation problem, and concentrates more specifically on irrigation water supply and storage. At representative sites, physical soil tests were performed and soil samples were collected for further study. Data on climate, hydrology, geology and soils were collected from various sources. For a year with average rainfall about one third of precipitation goes to deep percolation. This water is released from the subsoil and subsequently is gradually discharged by the rivers and streams which are the most important sources for irrigation. The quality of such water for irrigation is excellent. During the wet season water for irrigation is plentiful. The minimum river discharge in a year with average rainfall is 5 1/s.kmE2., sufficient to irrigate perhaps 5 to 10 percent of the Federal District. Groundwater could become an important irrigation water source, especially at high elevations. Water from springs is readily available and can be used for irrigation to a minor areal extent. Engineering tests show high initial infiltration and permeability properties of the soils which can be reduced by compaction at favorable moisture conditions.