Sap flow measuring on greenhouse tomato crop (Lycopersicon esculentum Mill.) under two irrigation levels

The method of constant heat input with a stem flow gauge was used to measure by a direct and not destructive way the transpiration of greenhouse tomato (Lycopersicon esculentum Mill. cv. 'Presto'). This method was used until now in open field crops but not in greenhouse. To check the practical use and the sensibility of the method the effects of two levels of irrigation were evaluated on sap flow, soil humidity, growth and development of greenhouse tomatoes. The experiment was conducted two years (1998 and 1999) on the same soil (covered with plastic mulch) from spring to summer in a plastic greenhouse without climate control. The water regimes corresponded the first year to 50% and 100% pan evaporation class A (Evb) and the second year to 35% and 100% Evb. The Evb was modified by a pan factor between 0.7 and 0.9 and a crop factor, that was ajusted from 0.3 to 1.3 according to crop development. During both years, the variables stem diameter, number of leaves, fruit setting and leaf area did not show differences between the two water levels. During the period of sap flow measurement (90 days) there were differences detected only on some days. But there were differences on the accumulated sap flow. It was 731 plant(-1) (1998) and 801 plant(-1) (1999) for the stressed treatment and in both years 1051 plant(-1) for the well watered treatment. The restriction of water application implied differences in plant height (the first year), soil humidity (both years), total and marketable yield (second year), great caliber fruit yield (second year) and a higher incidence of blossom end rot.