Trickle Irrigation; A Study of Moisture Distribution in the Soil Profile

139 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.Irrigation in Illinois has increased fourfold in the last decade. Sprinkler irrigation accounts for most of the irrigation in Illinois. While originating in arid regions of the world, trickle irrigation is beginning to receive notice in the humid and sub-humid sections of the United States. Whether trickle irrigation is a good supplementary irrigation system in an area of variable precipitation, similar to central Illinois, has not been investigated. The irrigation water requirement of vegetable crops for maximum yield and the effect of discharge rate on the distribution of moisture in heavy soils under a trickle source were subjects of this investigation.Tomatoes and bell peppers were trickle irrigated for two consecutive growing seasons in east-central Illinois. Results showed a considerable yield advantage for tomatoes using the highest level (1.0 Epan) of irrigation. However bell peppers responded better to a lower level of irrigation (0.5 Epan). Results are promising and indicate the feasibility of the use of trickle irrigation for the sub-humid Midwest area.Laboratory studies indicated that increasing trickle discharge rate resulted in an increase in the vertical component and a decrease in the horizontal component of the wetted zone. The percentage of applied water lost below the root zone and the volume of the wetted soil were related to the discharge rate. A comparison was made between the laboratory results and those computed using a simulation model (Bresler, 1975). The agreement between the predicted and measured soil moisture distribution pattern was generally quite good. A better correlation was found for lower discharge rates than higher ones. However, in most cases, the differences between the model prediction and measured values were in the 0-5 percent range. Pulsed treatments wetted more volume of soil with the same amount of applied water, and the downward restriction of soil moisture under pulsed application resulted in less water loss below the root zone.Based on both laboratory and field experiments, it was concluded that continuous discharge rates of greater than 4 liters/hour should not be recommended for trickle irrigation of crops grown on heavy soils similar to the experimental soil because of excessive water loss below the root zone and surface runoff problems.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD