Estimation of evapotranspiration from a field of linseed in central Italy

A study was carried out in central Italy into the evapotranspiration from linseed (Linum usitatissimum L.). In particular, the objectives were to (a) evaluate the accuracy of daily evapotranspiration estimates from partially incomplete Bowen ratio data; (b) measure seasonal evapotranspiration from linseed; (c) test the FAO 56 method for estimating crop coefficients for linseed and (d) calculate the surface resistance of the crop as a function of soil water status. The study was carried out on a crop of linseed growing in a 1.1 ha field near Viterbo using Bowen ratio apparatus. Soil water content and green area index were also monitored. It was found that (1) daily evapotranspiration could be estimated from partially incomplete Bowen ratio data on a continuous basis throughout the growing season; (2) the linseed crop lost 240 mm over the 100-day growing season; (3) measured crop coefficients agreed with those obtained using the FAO 56 methodology; (4) surface resistance could be expressed as a function of green area index and soil water deficit seemed to have an indirect effect by hastening leaf senescence.