Sap flow, leaf area, net radiation and the Priestley–Taylor formula for irrigated orchards and isolated trees

This paper describes the goodness of fit for two simple methods to estimate the daily sap flow of irrigated, non-stressed apple and olive trees in an orchard, and a walnut tree in isolation. The required inputs for the calculation are the tree leaf area (LA, in m2 tree−1), the net (all-wave) radiation over grass (RN, in MJ m−2 day−1) and the average air temperature. Data are presented for mid-summer when daily RN ranged between 2 and 20 MJ m−2 day−1. Tree leaf area ranged between 8.65 m2 for a dwarf apple and 35.5 m2 for a large apple.