Evaporative loss from irrigated interrows in a highly advective semi-arid agricultural area

Abstract

a b s t r a c tAgricultural productivity has increased in the Texas High Plains at the cost of declining water tables, putting at risk the sustainability of the Ogallala Aquifer as a principal source of water for irrigated agriculture. This has led area producers to seek alternative practices that can increase water use efficiency (WUE) through more careful management of water. One potential way of improving WUE is by reducing soil evaporation (E), thus reducing overall evapotranspiration (ET). Before searching for ways to reduce E, it is first important to quantify E and understand the factors that determine its magnitude. The objectives of this study were (1) to quantify E throughout part of the growing season for irrigated cotton in a strongly advective semi-arid region; (2) to study the effects of LAI, days after irrigation, and measurement location within the row on the E/ET fraction; and (3) to study the ability of microlysimeter (ML) measures of E combined with sap flow gage measures of transpiration (T) to accurately estimate ET when compared with weighing lysimeter ET data and to assess the E/T ratio. The research was conducted in an irrigated cotton field at the Conservation & Production Research Laboratory of the USDA-ARS, Bushland, TX. ET was measured by a large weighing lysimeter, and E was measured by 10 microlysimeters that were deployed in two sets of 5 across the interrow. In addition, 10 heat balance sap flow gages were used to determine T. A moderately good agreement was found between the sum E + T and ET (SE = 1 mm or $10% of ET). It was found that E may account for >50% of ET during early stages of the growing season (LAI < 0.2), significantly decreasing with increase in LAI to values near 20% at peak LAI of three. Measurement location within the north-south interrows had a distinct effect on the diurnal pattern of E, with a shift in time of peak E from west to east, a pattern that was governed by the solar radiation reaching the soil surface. However, total daily E was unaffected by position in the interrow. Under wet soil conditions, wind speed and direction affected soil evaporation. Row orientation interacted with wind direction in this study such that aerodynamic resistance to E usually increased when wind direction was perpendicular to row direction; but this interaction needs further study because it appeared to be lessened under higher wind speeds.

Soil profile method for soil thermal diffusivity, conductivity and heat flux: Comparison to soil heat flux plates

“…Values returned to near zero much more quickly after a peak for G grad than for G PS , likely also due to the inclusion of surface temperature in the divergence calculation. The observed diel spatio-temporal variation in G 0 parallels that observed for evaporation, E, from the soil surface as measured using microlysimeters by Agam et al 2012 [17]. As with G 0 , soil E peaked earlier in the day on the west side of the interrow and peaked later in the day on the east side of the interrow for N-S row orientation.…”

“…Evaporation (E) from the soil surface was measured using microlysimeters [17] and data are shown in Table 2 for the period when both G 0 and E data were available . This was mostly during the MID period.…”

“…The 24-h G PS sum was positive on three days (DOY 201, 213 and 215). DOY 201 was partly cloudy, but alfalfa reference ET [27,28] was still 5.9 mm [17]. On DOYs 213 and 215, alfalfa reference ET was 7.1 and 8.3 mm, respectively, due to the relatively clear skies and strong solar irradiance.…”

“…Evaporation [E] was measured on eight days and nights between DOY 198 and 215 using 10 microlysimeters (MLs) [17]. The MLs were made of 8-mm thick rigid white polyvinyl chloride (PVC) tubes with 105-mm inside diameter, 88-mm depth and metal bottoms.…”

“…(15); (2) Compare values of G 0 computed using the temperature gradient method (Eq. (5)) between the surface and a depth z = 0.02 m with those determined using soil heat flux plates buried at 0.08 m depth coupled with calorimetric correction to the surface; (3) Compare G 0 with the latent energy (LE) of evaporation from the soil surface as measured using microlysimeters by Agam et al [17]; and (4) assess the temporal and spatial variation of G 0 . Although it may be important, we do not in this article attempt to determine the depth range within which evaporative heat demand may be an important contributor to the measured G 0 , leaving that for a separate study.…”