|Evett, Steven - Steve|
Submitted to: International Water and Irrigation Review
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2000
Publication Date: N/A
Interpretive Summary: Drip irrigation tubing traditionally has been placed on the soil surface where it is easy to spot leaks or plugged emitters (the emitter is the part of the tubing that releases water to the plant). However, there may be substantial water savings if drip tubing is buried in the soil. This is because the surface application of water leaves the soil surface wet, leading to direct evaporation of the water to the air. This water is not available then to the plant but must still be added to the amount of water used by the plant to calculate the total water needed to irrigate a crop. We used a computer program called ENWATBAL (ENergy and WAter BALance) to simulate the effect on evaporation from the soil surface of burying drip tubing at depths of 6 and 12 inches versus leaving it on the surface. The simulation followed the development of a corn crop from sprouting to full growth and flowering. The model showed that the corn plants used the same amount of water regardless of where the tubing was placed, but there was much more loss of water from the soil surface if the tubing was placed at the surface. The least amount of evaporation occurred if the tubing was at a depth of 12 inches and so the amount of water needed to irrigate the corn crop was least when tubing was buried deeply. Over 3 inches of water was saved in this case. Almost all the differences in evaporation occurred before the plants reached their maximum height.
Technical Abstract: Drip irrigation using buried emitters has the potential to save irrigation water by reducing soil surface wetting and thus reducing evaporation (E). However, measurement of evapotranspiration (ET) for different combinations of emitter depth and cropping systems can become onerous. We used a mechanistic ET model, ENWATBAL, to simulate irrigation with drip emitters at depths of 0-, 15-, and 30-cm; and modeled energy and water balance components for corn (Zea mays L., cv. PIO 3245) grown on the Pullman clay loam soil at Bushland, TX. Irrigation was daily and was scheduled to replace crop water use as measured in the field by neutron scattering. Modeled transpiration was practically equal for all emitter depths (428 mm over 114 days from emergence to well past maximum leaf area index [LAI]), but evaporation was 51 mm and 81 mm less for 15- and 30-cm deep emitters compared with surface emitters. Predicted drainage was slight (6-, 8- and 12-mm for surface, and 0.15- and 0.30-m deep emitters, respectively), but comparisons of predicted and measured soil water profiles at season's end showed that deep drainage of over 150 mm of water may have occurred. There were minor differences in soil heat flux between the treatments and soil heat flux was a minor component of the energy balance. For surface emitters, net radiation was much greater and sensible heat flux was smaller than for subsurface emitters until LAI increased past 4.2 midway through the season. Thus, almost all of the differences in ET occurred during the period of partial canopy cover. Differences in energy balance components between treatments were minor after day of year 220. The study showed that water savings of up to 10% of seasonal precipitation plus irrigation could be achieved using 30-cm deep emitters.