‘Katja’ is a commercially important early season apple cultivar in Sweden. Difficulties such as very weak growth, rapid quality deterioration, and low fruit storage potential limit growers' ability to meet quality standards set by markets (http://www.algonet.se). These problems could be alleviated through better understanding of the close relationships between cultural practices and fruit storability (Tromp, 2005).
Pruning intensity, time, and method have varying effects on apple quality at harvest and during storage (Tomala, 1997; Wertheim, 2005). Winter pruning improves tree growth, fruit coloration, acidity, sugar content, and storability and increases fruit weight (Marini and Barden, 2004; Tahir et al., 2007). Summer pruning further improves fruit coloration and size but decreases yield and causes poor fruit storability (Fathi and Mukhtar, 1998; Goldschmidt, 1997; Tromp, 2005). Covering the soil surface in orchards instead of using herbicides can prevent weeds, change soil environmental conditions, improve availability of nutrients to trees, enhance vegetative growth, increase yield, and improve fruit storability (Rubauskis et al., 2002; Tahir et al., 2005). However, in some cases, soil covering can decrease fruit yield and sugar content (Fausett and Rom, 2001). Fertigation systems need careful adjustment, because higher nitrogen levels or excess water supply can cause poor fruit storability (Meheriuk et al., 1996; Rubauskis et al., 2002). Fertilization and irrigation normally increase trunk cross-sectional area and yield (Ghosh et al., 2004; Jadczuk et al., 2001). The international trend for organic cultivation practices rather than chemical has renewed interest in hand thinning (Pretorious et al., 2004). In most cases, thinning increases fruit size (Marini, 2004; Tomala, 1997), firmness, and sweetness (Basak, 1999; Bergh, 1990) and improves superficial color (Link, 2000). Although some studies report no visible effects of thinning on fruit storability (Krzewinska et al., 2002), others report a tendency for decreased storage potential related to thinning (Wójcik et al., 2001) and decreased yield (Basak, 1999).
Most studies relating apple fruit quality to orchard management procedures involve individual testing of each practice. This study sought to improve ‘Katja’ apple quality and storability by combining different management practices, namely application of bark mulch, pruning, hand thinning, and nitrogen fertigation, regulated at two different levels, resulting in 16 treatments.
Bepete, M. & Lakso, A.N. 1998 Differential effects of shade on early season fruit and shoot growth rates in ‘Empire’ apple branches HortScience 33 823 825
Choi-Seong, Y. & Choi, S. 2000 The effect of mulching material on the shoot and root growth and fruit quality of ‘Fugi’/M.26 apple J. Korean Soc. HortScience 41 512 516
Fathi, M.A. & Mukhtar, H. 1998 Influence of summer pruning on growth, fruit set and fruit quality of Anna apple trees Egypt. J. Agr. Res. 76 721 732
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Ghosh, S.N., Manna, S. & Mathew, B. 2004 Effect of nitrogen and potassium fertilization on custard apple grown under rain fed late rite soils Environ. Ecol. 22 144 147
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Jadczuk, E., Pietranek, A. & Dziuban, R. 2001 Irrigation and K fertilization effects on the cropping and fruit quality of ‘Katja’ apple trees on four different rootstocks Folia. Hort. 13 47 60 (abstr.)
Krzewinska, D., Basak, A., Mika, A. & Michalska, B. 2002 The effect of time and intensity of hand thinning on the distribution of apples in size and colour classes Zeszyty Naukowe Instytutu Sadownictwa i Kwiaciarstwa W Skierniewicach 10 89 99 (abstr.).
Marini, R.P. & Barden, J.A. 2004 Yield, fruit size, red colour, and a hand economic analysis for ‘Delicious’ and ‘Empire’ in the NC-140 1994 System Trail in Virginia J. Amer. Pomol. Soc. 58 4 11
Meheriuk, M., Mckenzie, D.L., Neilsen, G.H. & Hall, J.W. 1996 Fruit pigmentation of four green apple cultivars responds to urea sprays but not to nitrogen fertilization HortScience 31 992 993
Pfammatter, W. & Dossimoz, A. 1997 Influence of irrigation and ground cover on development and yields of young apple trees Revue. Suisse. De. Viticulture. D'Arboriculture et d'Horticulture 29 301 304
Pretorious, J.J.B., Wand, S.J.E. & Theron, K.L. 2004 Fruit and shoot growth following combined girdling and thinning of ‘Royal Gala’ apple trees Acta Hort. 636 401 407
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Rubauskis, E., Skrivele, M., Dimza, I. & Berlands, V. 2002 The response of apple trees to fertigation and mulch Sodininkyste ir Darzininkyste. 21 126 133
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Tromp, J. 2005 Mineral nutrition 55 63 Tromp J., Webster A.D. & Wertheim S.J. Fundamentals of temperate zone tree fruit production Backhuys Publishers Leiden, The Netherlands
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Wójcik, P., Rutkoeski, K. & Treder, W. 2001 Quality and storability of ‘Gala’ apples as affected by crop load Folia Hort. 13 89 96 (abstr.)
Ystaas, J. 1992 Effects of summer pruning on yield, fruit size, and fruit quality of the apple cultivar ’Summerred’ Acta Hort. 322 277 282