The influence of root patterns is more difficult to take into account. The differences in the two lines shown in Figure 16b are interesting in that they are likely due to differences in root volume and density arising as a consequence of different wetted volumes and different irrigation frequencies: a high density and small volume for drip irrigated trees, while the others had a larger volume of soil explored by roots (mini-sprinklers) being used to moderate stress between irrigations. A poorer adaptation to water stress for the drip irrigated orchard apparently promoted a sharper decrease, which is consistent with the expected results from the analysis on limitations to water movement in soil.
The challenge, mainly for woody crops with deep roots, is to predict how these lines change. In a tentative to minimize this problem, the relationship can be adjusted from in loco measurements. For instance, the relationship Ks - yp allows the construction of a double scale yp and Ks (YY') for the relationship with E ETa (XX'). Let's suppose measurements of yp and soil water depletion are performed in loco. If a certain yp (= to an equivalent value of Ks) provides the value for EETa estimated by the first tentative relationship, it means it is well adjusted. If not, the line will be corrected according to the information obtained and the calculation of EET is verified with appropriate algorithms. Repeating the checks, a corrected relationship can be obtained.
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