Book of Abstracts

30
New technique for measuring surface energy balance and soil water evaporation beneath sparse plant
canopies
Thomas Sauer; Soil, Water, and Air Resources Research Unit; USDA-ARS-NLAE; Ames, Iowa, United States;
tom.sauer@ars.usda.gov
Non-uniform surfaces, like sparse canopies in arid environments, offer unique challenges for the measurement of the
surface energy balance and evapotranspiration (ET). Obtaining separate measurements of soil water evaporation (E)
and plant transpiration (T) is often critical to improving irrigation water-use efficiency. Sap flow techniques can be
used to measure T of individual plants, but the apparatus is expensive and requires frequent attention, and scaling up
to the canopy level can be challenging. Measurement of E can be accomplished by micro-lysimeters or soil water
balance techniques, but both techniques often require many replicate measurements to deal with spatial variation.
We developed a micro Bowen ratio energy balance (MBREB) measurement system to determine E beneath and
between rows of vineyards in arid southern Israel and humid western North Carolina, USA. The system measured
air temperature and water vapor pressure 1 and 6 cm above the soil surface. Net radiation (Rn) was measured with
three types of net radiometers, and soil heat flux (G) was measured with flux plates. An eddy covariance system
above the canopy measured ET for the vineyard. T was measured with sap flow gauges, and E was measured with
micro-lysimeters and heat dissipation sensors over select intervals for comparison. Overall, the MBREB approach
showed great promise although some challenges remain. Accurate measurements of very small vapor pressure
gradients and large temperature gradients so near the soil surface require special care. Uncertainty in the
measurement footprint and the complex, dynamic solar radiation pattern in the vineyard make selection of the
relevant net radiometer viewing area challenging. The MBREB has several advantages, including continuous
measurement, no soil disturbance, a relatively large footprint providing good spatial averaging, and the potential to
also obtain soil CO2 flux data.
Sustainable agriculture in water-stressed, arid regions using aeroponics
Navin Kumar C. Twarakavi, Associate Professor, Desert Research Institute, Las Vegas, NC 89119. Phone: 001-
702-715-7223. Email: navin.twarakavi@dri.edu
With agriculture contributing minimally to the economy of Nevada under conditions of a burgeoning population and
increased stress on the availability of food and water, the future is highly dependent on the sustainable growth of its
urban centers (such as Las Vegas and Reno). Given that tourism is a major industry in Nevada, the need for high
quality fresh produce cannot be understated. Currently, fresh produce (such as fruits and vegetables) are imported in
to Nevada, both nationally and internationally. There are a number of issues associated with the transportation of
fresh produce to cater to the demands of Nevadans. Firstly, the carbon footprint of transporting fresh produce is
quite significant. Research has shown that growing fresh produce causes 5% of a person’s carbon footprint each
year. However, when this fresh produce has to be transported long distances, the amount of the carbon footprint
changes to 28%. Secondly, transportation of fresh produce results in a loss of taste and nutritional quality and a
decreased shelf-life. Also, depending on the type of fresh produce, the cost of transportation can be as high as 30%
of the total cost. The above-stated issues are especially true in the case of “cash” crops, such as micro-greens,
nutraceuticals, and spices, among others. In order to grow non-local food locally, greenhouses have been used in the
past. Other systems, such as hydroponics, have been introduced to address the same issue. However, these
approaches do not reduce the water demand, which is not suitable in water-stressed environments such as Nevada.
Systems that allow for high production rates, higher yield/ acreage and year-round production would be suitable.
Aeroponic systems are ideally suited to address these requirements. Here, we present aeroponic systems that are
currently being adapted for Nevada to encourage sustainable agriculture.
Modelling the water balance in low rainfall cereal systems of Southern Australia
Anthony M. Whitbread 12 and Jeff A. Baldock 3
1 CSIRO Ecosystem Sciences, Waite Precinct, Adelaide; awhitbr@gwdg.de