Partitioning almond evapotranspiration

Samantha Conner will be taking measurements of evporation rates from soil in an almond orchard. Samantha will be working as part of the larger research project “Developing a reliable model of drainage production from irrigated horticulture at the farm and district level". Samantha will be undertaking her project as part of her final year of undergraduate studies at Flinders University.

The measurements Samantha takes will enable measures of whole of orchard evapotranspiration to be separated into productive and non-productive components. With these measures the project can validate the applicability of both single and dual cop coefficient approaches to the estimation of almond crop evapotranspiration.

Recent Activities

This project will be undertaken from December 2008 to January 2009 and will form part of Samantha’s honours thesis.

Aims

1. A report on the quantification of soil water evaporation in a mature almond orchard.
2. Generation of a data set which when combined with measures from the associated project can provide the basis of a honours thesis directed at investigating the “single” crop coefficients (used to estimate total
evapotranspiration from weather data) and dual crop coefficients (used to separately estimate crop transpiration and soil water evaporation) approaches to estimation of crop water use form meteorological data.
3. To gain field work experience.

Background

Water is a public asset. Irrigators are the largest users of this asset and there is increasing pressure for them to report on the economic, environmental and social outcomes of its use. The Irrigation Reporting and Evaluation System(IRES) has been developed to support systematic reporting on economic and environmental outcomes at a district level. A key input in IRES, and other programs in this area, is the relationship between crop water use and weather. For each crop this relationship is described by a single set of crop coefficients (ratio of crop water use to reference crop water use). Past approaches used in validation of these relationships have had strong spatial limitations. Some of these limitations are currently being addressed in almond crops by applying an eddy covariance technique to the determination of
crop coefficients at Loxton on the River Murray in South Australia.
Water use by a crop can be divided into productive water use (crop transpiration) and non-productive water use (soil water evaporation). Productive use rates are sensitive to irrigation application methods, for example soil water evaporation with sub-surface drip is less than that with flood. The effect of irrigation methods on crop water use cannot be estimated from approaches which use a single set of crop coefficients. IRES currently employs such an approach. The irrigation effect can be accounted for by using a “dual crop coefficient” approach to the estimation of evapotranspiration. One set of coefficients accounts for crop transpiration and another set for soil water evaporation.

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