|Agam, Nurit -|
|Chavez, Jose -|
Submitted to: Advances in Water Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2012
Publication Date: November 29, 2012
Citation: Agam, N., Evett, S.R., Tolk, J.A., Kustas, W.P., Colaizzi, P.D., Alfieri, J.G., McKee, L.G., Copeland, K.S., Howell, T.A., Chavez, J.L. 2012. Evaporative loss from irrigated interrows in a highly advective semi-arid agricultural area. Advances in Water Resources. 50:20-30. Interpretive Summary: Use of groundwater from the Ogallala Aquifer for irrigation has transformed the High Plains into one of the largest and most productive agricultural regions in the United States. It has earned the nickname "breadbasket of the world." Unfortunately, the agricultural productivity of the region has come at the cost of declining water tables. This puts at risk the sustainability of the aquifer as a principle source of water for irrigated agriculture and for public and domestic drinking supplies. Groundwater depletion has increased pumping costs. The decrease in profits has led producers to begin looking for alternative practices that can increase economic yield per unit of water used. This would improve the profitability of production systems. Evaporation from the soil surface is a significant component of the water balance that may account for 30-60% of seasonal total crop water use. But, evaporation does not directly contribute to crop yield. Scientists at the USDA-ARS laboratory, Bushland, Texas, studied methods to measure evaporation loss and its relationship to crop row direction, crop height and time since irrigation. They found that orienting crop rows at right angles to the direction of the strongest and hottest winds could decrease evaporation loss by 20%. Also, applying deeper irrigations and increasing the interval between irrigations would decrease evaporation losses because those losses are greatest immediately after an irrigation.
Technical Abstract: Agricultural 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 begin looking for 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 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 about 10% of ET). It was found that E may account for greater than 50% of ET during early stages of the cotton growing season (LAI less than 0.2), significantly decreasing with increase in LAI to values near 20% at peak LAI of 3. 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 was usually decreased when wind direction was parallel to row direction; but this interaction needs further study because it appeared to be lessened under higher wind speeds.