The evaporative cooling effects of overtree microsprinkler irrigation on 'Mondial Gala' apples

Microsprinkler irrigation for evaporative cooling of 'Mondiall Gala' apples (Malus x domestica Borkh.) was evaluated over a 3-year period in Lleida (NE Spain). Cooling irrigation was applied continuously for 2 It on a daily basis for 25-30 days prior to commercial harvest. Three treatments were evaluated: (1) control without overtree microsprinkler irrigation: (2) microsprinkler irrigation applied at sunset; (3) microsprinkler irrigation applied at mid-day (year 2) or at sunrise (year 3). Fruit and orchard temperature were significantly reduced by cooling irrigation, especially when applied at mid-day and at sunset. Fruit colour, as measured with a Minolta CR-200 portable triestimulus colourimeter using the CIE [1976] L*a*b* system, and anthocyanin concentration were significantly affected by both the cooling irrigation and the weather of each specific year. The years 1998 and 1999 were warm years typical of the region and cooled fruits had better colour than in the control. In 1997. on the other hand, low temperatures and rainfall prior to harvest masked the effects of cooling irrigation on fruit colour and quality parameters. Microsprinkler irrigation, especially when applied at sunset, increased the red colour, providing eater surface colouration and higher anthocyanin content on both sides of the fruit. A linear regression of anthocyanin content on L*, a*lb* ratio and hue angle provided R-2 values of 0.58,0.52 and 0.58, respectively. These values are low for estimating fruit anthocyanin content in situ from chromaticity values. Based on the colour required to meet EU grade standards, 13-22% more fruits were harvested at first pick from trees receiving cooling irrigation than from the control. Fruit firmness, fruit size. and soluble solid concentration (SSC) were all increased by cooling irrigation, though the extent to which this occurred varied from season to season. Significantly greater values were observed for cooled fruits than the control in 1998 and 1999 but not in 1997. On the other hand, titratable acidity (TA) did not appear to be consistently affected by evaporative cooling. The economical analysis evidences the interest of cooling, due mainly to increase of fruit colour, especially when the same system is used for both purposes, frost protection and cooling. (C) 2004 Elsevier B.V. All rights reserved.