Fruit size, yield, and market value of 'GoldRush' apple are affected by amount, timing and method of nitrogen fertilization

Abstract

'GoldRush' is a new scab (Venturia inaequalis) resistant apple (Malus xdomestica) with excellent flavor and storage qualities that tends to produce small and russeted fruit. We investigated the effects of rate, timing, and method of nitrogen (N) fertilizers on 'GoldRush' fruit size and quality during 1998-99. Fertilizer treatments were 1) no N fertilizer (control); 2) a low N rate of 45 kgha-1 (40.1 lb/acre) applied in April (LN-Apr); 3) a low N rate of 45 kgha-1 applied half in April and half in June (LN-Apr+Jun); 4) a high N rate of 90 kgha-1 (80.3 lb/acre) split in April and June (HN-Apr+Jun); 5) a high N rate of 90 kgha-1 applied in April, May, June, and July at 22.5 kgha-1 (20 lb/acre) each month (HN-Apr+May+Jun+Jul); and 6) canopy sprays of 1% (wt/wt) urea-N, equivalent to 7 kgha-1 (6.2 lb/acre) applied monthly in May, June, July, and August (foliar urea). In 1998, an additional foliar urea spray at 5% (wt/wt) concentration was applied to trees after harvest. The first year's N treatments did not affect relative average fruit weights or total yields, but unfertilized trees produced more fruit in smaller size categories. Nitrogen fertilization resulted in greener and softer fruit both years. In the second year, all N additions increased yields compared with controls, but average fruit weight was inversely correlated with crop load. Foliar urea sprays and HN-Apr+May+Jun+Jul treatments increased yields the most. Fruit from LN-fertilized trees were normally distributed across a range of eight box-count size categories, peaking at size 100 both years. In the unfertilized control, fruit size was skewed into smaller size categories and yield was reduced. Total yields were greatest in foliar urea and HN-Apr+May+Jun+Jul treatments, but fruit-size distribution was skewed into smaller categories, peaking at size 138 in the second year. Foliar urea and HN-Apr+May+Jun+Jul treatments produced the highest crop value, but when estimated labor and fertilizer costs were considered, foliar urea and LN-Apr+Jun were the most efficient treatments. Nitrogen fertilizer improved fruit size and market value, but average fruit size in all treatments remained relatively small in both years, indicating that N fertilization alone may not increase fruit size in 'GoldRush'.