Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

Abstract

Sprinkler irrigation efficiency declines when applied water intercepted by the crop foliage, or gross interception (Igross), as well as airborne droplets and ponded water at the soil surface evaporate before use by the crop. However, evaporation of applied water can also supply some of the atmospheric demands usually met by plant transpiration. Any suppression of crop transpiration from the irrigated area as compared to a non-irrigated area can be subtracted from Igross irrigation application losses for a reduced, or net, interception (Inet) loss. This study was conducted to determine the extent in which transpiration suppression due to microclimatic modification resulting from evaporation of plant-intercepted water and/or of applied water can reduce total sprinkler irrigation application losses of impact sprinkler and low energy precision application (LEPA) irrigation systems. Fully irrigated corn (Zea Mays L.) was grown on 0.75 m wide east-west rows in 1990 at Bushland, TX in two contiguous 5-ha fields, each containing a weighing lysimeter and micrometeorological instrumentation. Transpiration (Tr) was measured using heat balance sap flow gauges. During and following an impact sprinkler irrigation, within-canopy vapor pressure deficit and canopy temperature declined sharply due to canopyintercepted water and microclimatic modification from evaporation. For an average day time impact irrigation application of 21 ram, estimated average Igross loss was 10.7%, but the resulting suppression of measured Tr by 50% or more during the irrigation reduced Igross loss by 3.9%. On days of high solar radiation, continued transpiration suppression following the irrigation reduced Igross J. A. Tolk ([]) 9

Evaporation Research: Review and Interpretation

“…14 by Thompson et al (1997) demonstrated that even with the short irrigation water contact time with a crop that is associated with a linear-move irrigation system, daily T is suppressed relative to T where an irrigation event does not occur. Tolk et al (1995) measured similar suppression with stem flow measurements and attributed the reduction to evaporation of canopy-intercepted water and microclimatic modification. Total ET for the day increased for the irrigated relative to the nonirri- gated scenarios due to the introduction of readily evaporable water to the soil and the low resistance to evaporation of free water on the leaves.…”

“…Net crop canopy-interception loss was defined in Mc Naughton (1981) as the difference between the T from a nonirri gated area and the gross interception loss from an identical area that is irrigated. Tolk et al (1995) also noted that "transpiration recovery to near pre-irrigation levels was rapid, with additional transpiration suppression of 1-3% occurring only on days with high solar radiation. "…”

“…The evapotranspiration for the above three cases was not inte grated with time for a quantitative comparison of the impact of the different irrigation conditions and the interception evapora tion. However, Tolk et al (1995) made some conclusions about this issue. They made stem flow measurements of transpiration reductions for well-irrigated COrn with impact sprinklers on a lin ear move system in Bushland, Tex.…”

Evolution of Corn Transpiration and Leaf Water Potential During Sprinkler Irrigation

“…However, during daytime sprinkler irrigation, the crop microclimate is modified. Decreases of water vapor pressure deficit (VPD) and air temperature have been reported (Robinson, 1970;Steiner et al, 1983b;Tolk et al, 1995). The decrease in VPD would result in some reduction of the crop transpiration rates, leading to the conservation of soil water, which would otherwise be depleted by the crop (McNaughton, 1981;Steiner et al, 1983a).…”

“…Due to this reduction of transpiration, some part of the application water losses during the irrigation event should not be considered as true losses. Consideration of net evaporation losses instead of gross evaporation losses would result in an increase of application efficiency for a given application depth (McNaughton, 1981;Tolk et al, 1995;Martínez-Cob et al, 2008). In addition to this beneficial effect of daytime sprinkler irrigation, the reduction in VPD would also result in a recovery of LWP during the irrigation events.…”