Crop yield response to water - Cra

Apples tend to have a biennial bearing pattern where the degree of biennial bearing varieswith varieties (Lauri et al., 1996) and potential crop yield is highly affected by the timing offruit thinning and the crop load in the previous season.Stages of development in relation to yield determinationBloom date varies with varieties and climatic regions. Most varieties flower in April (NorthernHemisphere), whereas early (low chilling requirement) varieties can bloom at the end ofFebruary and early March. Apple fruit has an expo-linear growth pattern where much of thedry mass accumulation occurs in the linear phase that starts ~30 days after full bloom in somevarieties while in others the linear phase starts ~60 days after full bloom (Goffinet et al., 1995)Figure 2 shows the patterns of fruit growth as affected by different irrigation treatments.The reproductive cell division phase lasts 40-50 days post bloom (Westwood, 1993).Fruit size is a major determinant of fresh fruit quality and is highly dependent on tree waterstatus and irrigation. However, there are many other factors that will affect the response of fruitsize to irrigation including the number of cells in the fruit pericarp, crop load, the number ofseeds per fruit, factors that interact with each other.Temperatures lower than 25 °C during the reproductive cell division phase reduce apple fruitsize (Tromp, 1997 and Warrington et al., 1999); on the other hand, it has been found that thenumber of cells in apples decreased when the trees were grown at 35/15 °C (day/night) ratherthan at 25/15 °C. This suggests that there is an optimum temperature for reproductive cellFigure 2Seasonal patterns of apple fruit growth in response to various irrigation treatments: Dark andlight blue, grey and red – 100 percent of estimated ET c for various drip irrigation arrangements;Dark and light green – 100 percent of estimated ET c applied after two years of severe waterrestrictions (between 50 to 70 percent of estimated ET c ); Light and dark orange, black andviolet - Different water restriction levels (50 - 70 percent of estimated ET c ) (Girona et al., 2011and unpublished data).300250200Fruit volume (ml)150100500100300 500 700 900 1 100 1 300 1 500 1 700Acumulated degree days334crop yield response to water