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Title: Drip irrigation water distribution patterns: Effects of emitter rate, pulsing, and antecedent water

item Skaggs, Todd
item Trout, Thomas

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2010
Publication Date: 11/1/2010
Citation: Skaggs, T.H., Trout, T.J., Rothfuss, Y. 2010. Drip irrigation water distribution patterns: Effects of emitter rate, pulsing, and antecedent water. Soil Science Society of America Journal. 74(6):1886-1896.

Interpretive Summary: Soil fumigation is often required in agriculture to control pests and pathogens. Increasingly, drip irrigation systems are being used to apply fumigants. The effectiveness of these systems in controlling pests and pathogens depends on their ability to disperse the fumigant throughout the shallow soil where plant roots grow. The horizontal distance that water and fumigant will travel through the soil from a drip emitter determines the required spacing and number of drip emitters, and hence the cost of the system. It has been proposed, though not proven, that certain management techniques can enhance the horizontal movement of water and fumigant, and thus reduce costs by reducing the number of emitters required. In this work, we investigated management practices proposed to enhance horizontal water spreading. We found that two of the practices, low application rate and pulsed application, had a negligible effect on water spreading. A third practice, pre-wetting of the soil, significantly enhanced spreading, although the increases were in all directions and not preferentially in the horizontal direction. This research will be of interest to growers and consultants working with drip irrigation systems, and it will help other scientists and engineers develop drip irrigation and fumigation management practices that maximize crop yields while conserving and enhancing soil, air, and water resources.

Technical Abstract: Drip irrigation is more effective and less expensive if a large amount of soil can be wetted with each emitter without losing water or nutrients below the root zone. The distance that water spreads horizontally from a drip line is a limiting factor that determines the spacing and number of drip lines and emitters, the frequency of irrigation, and thus the cost of irrigation. We used numerical simulations and field trials to investigate the effects of application rate, pulsed water application, and antecedent water content on the spreading of water from buried drip emitters. Simulation results showed that pulsing and lower application rates produced minor increases in horizontal spreading at the end of water application. However, the observed increases were simply due to longer irrigation times, and not due to any flow phenomena associated with pulsing or low emitter rates. Moreover, the small increases observed at the end of irrigation mostly disappeared after the infiltrated water had redistributed for a period of 24 h. Field trials confirmed the simulation findings, with no statistically significant difference in wetting being found among five water application treatments involving pulsed applications and varying discharge rates. The simulations confirmed that higher antecedent water content (such as may be achieved with frequent irrigation) increases water spreading from drip irrigation systems, but the increases were greater in the vertical direction than in the horizontal, an undesirable outcome if crop roots are shallow or groundwater contamination is a concern. Overall, soil texture (hydraulic properties) and antecedent water content largely determine the spreading and distribution of a given water application, with pulsing and flow rate having very little impact.