Effects of Nitrogen, Potassium, Irrigation and Crop Load On Honeycrisp Fruit Quality

Two field studies were planted in 2002 using Honeycrisp apple trees on M.9 rootstock. The first experiment compared soil applied nitrogen (0 and 100 kgN/ha), potassium (0 and 200 kgK2O/ha) and irrigation (none and trickle irrigation) in a factorial treatment scheme from 2002-2006. The second study compared foliar fertilizer treatments of N,B,Zn,Mg and Ca, and irrigation in a factorial treatment scheme from 2002-2006. From 2004-2006 four crop loads (0, 4, 8, 12 fruits/cm2 TCA) were imposed on whole trees as a subplot treatment. Nitrogen soil fertilization increased tree growth in the first two years but not after cropping began. Nitrogen fertilization increased fruit size, yield, soluble solids and rot incidence but resulted in reduced red color, firmness and total value of the crop in two years. Potassium fertilization increased shoot and tree growth, fruit size, red color and total crop value but reduced fruit dry matter concentration. Irrigation increased shoot and tree growth, yield and fruit size but reduced fruit soluble solids and increased crop value in only 1 year. The combined effects of rainfall and irrigation were evaluated by calculating annual water balance and correlating tree and fruit responses to water balance over the 3 years. Fruit red color, size, incidence of soggy breakdown and incidence of soft scald were positively related to annual water balance while fruit firmness, soluble solids, bitter pit incidence and rot incidence were negatively related to water balance. Bitter pit incidence was most influenced by water balance during the early season near petal fall. Crop load had a negative effect on shoot and tree growth, fruit size, firmness, soluble solids and dry matter concentration. Increasing crop load reduced storage disorders (especially bitter pit), fruit rots and percentage of bad fruits. Crop value increased with increasing crop load up to 8-10 fruits/cm2 TCA. Foliar nutrient sprays has little effect on tree growth, yield or fruit quality. Ca sprays reduced bitter pit incidence in only 1 year. Fruit mineral concentrations and ratios of nutrients were correlated with fruit responses. Fruit P/S ratio was positively related to fruit red color. Fruit Ca content was not related to fruit firmness or bitter pit incidence. Fruit P concentration was positively related to incidence of bitter pit. Fruit Ca/water ratio and fruit P concentration were positively related to fruit dry weight, whereas fruit Ca was negatively related to it. Fruit S content was positively related with blue mold incidence.