Cranberry Fall Nitrogen Fertilization Promotes Subsequent-season Vegetative Growth

Plant reserves play a key role in woody perennial plant winter survival and growth resumption in the spring. In fruit crops, reserves are critical for production in temperate climates when nutrient uptake is minimal and photosynthate production is limited in newly emerged leaves. Fall nitrogen (N) fertilization can be used to increase the availability of plant reserves to support and enhance vegetative growth and fruit production the following growing season. The objective of this study was to test the effect of fall N fertilization on fruit production by evaluating yield components and their relationships to vegetative growth. A split-plot design was established in three ‘HyRed’ cranberry production beds at a farm in central Wisconsin in a 3-year study. Fall N treatments were the main effect and consisted of plots receiving a single application of 0%, 10%, 20%, and 40% of the standard N application (67 kg⋅ha–1) used during the growing season. Summer N fertilization treatments were split in five weekly applications as subplots and consisted of a complete (100%) and a balance (60%, 80%, and 90%) of the standard N application (67 kg⋅ha–1) used during the growing season. Yield was unaffected by either the fall or summer fertilization treatments, but there was an increase in berry weight and a reduction in the number of fruit per unit area using the 40% fall N fertilization treatment. The lower number of fruit per unit area resulted from an increase in the proportion of vegetative uprights—a phenomenon related to an increased length of uprights. Prolonged growth may have affected the flower bud induction window, which occurs in early fall. The fall N fertilization effect of increased vegetative growth may have been the result of an increased availability of N in spring. This result could be advantageous in the establishment of new beds or the recovery of vines that have experienced stress.