Field Representative Elementary Volume (FREV) for Water Content in Regularly Irrigated Soils: A Case Study in an Arid Loamy-Sand Soil.

Thursday, 27 July 2017: 10:30 AM
Paul Brest West (Munger Conference Center)
Effi Tripler, Central and Northern Arava R&D, Soil and Water Sci., Sapir, Israel, Yechezkel Mualem, Central and Northern Arava R&D, Soil and Water Sci., Rehovot, Israel and Uri Shani, The Hebrew University of jerusalem, Soil and Water Sci., Rehovot, Israel
Abstract:
In regularly irrigated soils, water application management is based upon predetermined, consistent criteria for irrigation. This type of management is common in areas characterized with sophisticated and intensive farming practices and automated irrigation. The spatio-temporal pattern of water content in irrigated soils results from the natural spatial variation of the porosity (Russo and Jury, 1987). Irrigation management is often involved with volumetric averaging of q for calculating water balances. The hypothesis of this work is unique for regularly irrigated fields, in which a deterministic spacing of plants and irrigation point source is likely to be found. Under this state, an FREV (Field Representative Elementary Volume) can be calculated, in which multiple samplings of q yields low variation. Means of q within the FREV, determined from a specific sampling pattern will yield the same values as in the entire field.

Three dimensional measurements of q  in the root zones of pepper (Capsicum annuum L., cv. Cannon), were performed under several lateral dripper discharges, by means of a network of TDR probes spaced 10x10 cm. Water content data were then uploaded to a Matlab program that calculated the threshold FREV, according to Bear (1972) . Semi-variograms were used for calculating the spatial variance, as well as the FREV. Similarly, the variable root water uptake which was studied by means of the geo-statistical methods, analyzed the dynamics of the spatial pattern of q, along the growing season.

The elementary volume in regularly irrigated soils is descriptive for a representative phyto-hydrological unit, solely dependent on the deterministic spacing pattern of plants and irrigation sources. The spatial pattern of the roots develops according to the 3-D water content distribution. Consequently, the practical implications of the FREV are: [1] definition and quantification of dynamic processes in a field should be based upon sampling volume equals to the FREV; [2] the phyto-hydrological volume can be used by mathematical models, as a representative unit; [3] growing containers (lysimeters) having equal or greater volume than the calculated FREV, placed in fields, can accurately calculate water and ion balances.

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