Dwarfing rootstocks have been economically advantageous in the production of apple (Malus ×domestica Borkh.) by increasing the precocity and unit area yield of closely spaced trees (Quamme et al., 1997). Modern sweet cherry (Prunus avium L.) orchards based on dwarfing, precocious, and productive rootstocks are similarly advocated as inherently more profitable than low-density plantings where vigorous growth, large tree size, and delayed production act to decrease economic return (Whiting et al., 2005). A major management issue concerning cherry production on dwarfing rootstocks has been the possibility of reduced fruit size (Franken-Bembeck, 1998). Hence, a number of bloom (Whiting et al., 2006) and postbloom (Lenahan and Whiting, 2006) strategies are being researched in the Pacific Northwest and show potential to increase fruit size in some years. In Europe, dormant spur thinning has been advocated as a method of improving fruit size (Lauri and Claverie, 2005), but this method has not been systematically assessed under Pacific Northwest growing conditions. Crop load adjustment has the potential to affect other cherry attributes such as soluble solids concentration (SSC), although effects are not always consistent (Whiting et al., 2006).
Limited information is available concerning nutrient and water application strategies for optimizing yield and quality of sweet cherry, especially when grown on dwarfing rootstocks (Hanson and Proebsting, 1996). Our previous research indicated that fertigation method affected tree size and nutrition but had minimal effects on fruit quality in the first four growing seasons, when cropping was initiating and yields were low (Neilsen et al., 2004a). It is unknown whether relationships established between tree performance and fertigation for young plantings would persist as trees crop more heavily. For other fruit crops such as apples, high crop loads can depress leaf K concentration (Hansen, 1980) and decrease fruit size in an interaction with amount of applied irrigation (Naor et al., 1997). It is not known whether such relationships would be pertinent to sweet cherry, which has a short growing season and partitions less dry matter to fruit relative to vegetative growth (Kappel, 1991).
Thus, a study was undertaken with ‘Lapins’ on Gisela 5 with the objectives of testing the effects of crop load adjustment through dormant spur thinning and fertigation treatments on yield, nutrition, and quality of sweet cherry in high-density plantings.
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