FLOOD IRRIGATION OF A CRACKED SOIL

An understanding of water flow into cracking, irrigated soils is neces sary in order to address problems of plant water stress, inefficient w ater application, lack of aeration, and salt accumulation in the soil due to inadequate leaching. The objectives of this study were to inves tigate water infiltration into a cracked clay soil during flood irriga tion, and to observe the differences in infiltration and cracking patt erns between fallow soil following wheat (Triticum turgidum L. 'Yecoro Rojo') and soil under alfalfa (Medicago sativa L. 'CUF 101'). A large weighing lysimeter was used to measure infiltration and evaporation. The infiltration was analyzed as consisting of three phases of crack f illing, sorption, and transmission. The infiltration curves were found to be similar for all irrigations, with a larger percentage of the to tal infiltrated water initially entering the cracks of the drier alfal fa soil (74%) than the wheat-cropped soil (63%). Final infiltration ra tes were 0.4 and 0.6 mm h-1 for the alfalfa and wheat irrigations, res pectively. Evaporation was shown to be a large component of water loss during the later stages of irrigation, sometimes exceeding the infilt ration rate. Cracking patterns could be observed because of the presen ce of foam, which consists of organic acids picked up by water rising in the cracks. The wheat-cropped fallow soil had more numerous cracks than alfalfa-cropped soil, which was attributed to its fiberous root s ystem, which is weaker than the alfalfa taproot system. The difference in cracking patterns between the two crops has implications for water flow.