Energy and water balances for surface and subsurface drip irrigated corn

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 modified a mechanistic ET model, ENWATBAL, to simulate irrigation with drip emitters at any depth 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 using emitters at the surface and at 0.15- and 0.30-m depths. Irrigation was daily and was scheduled to replace crop water use as measured in the field by neutron scattering. Modeled transpiration was essentially 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 because soil heat flux was a relatively 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.