Response of Concord Grape to Variable Rate Nutrient Management

Abstract

Nutrient management of Concord grapes (Vitis labruscana L.) involves spring application of granular fertilizers broadcast between rows. This technique makes possible the use of variable rate application (VRA) of fertilizer, a technology that has been evaluated and used in annual crops but that has had little use in perennial crops. Over a four-year period, VRA nitrogen (N), phosphorus (P), and potassium (K) fertilizer were applied across a 4-ha vineyard block. Soils, both surface (zone of fertilizer addition) and subsurface (root zone), were collected in the spring to enable fertilizer VRA and to assess the effect of previous year application on soil nutrient availability. Soil and tissue (leaf petiole and blade) samples were collected during the growing season to evaluate crop nutrient status. Yield was assessed with a yield-monitoring system. Spring soil test results were used to measure change in response to four years of N, P, and K fertilizer VRA. Soil test N variability decreased and K variability was little affected. Soil test P variability in the surface soil remained relatively constant, but subsurface P increased in variability with time. This research found that VRA fertilization did not reduce in-field juice grape yield variability. Yield was positively responsive to N fertilizer, virtually nonresponsive to P fertilizer, and negatively responsive to K fertilizer. Results also indicated that when tissue testing was related with yield response, it was to leaf blade, rather than to petiole, tissue. This research suggests that VRA technology may be useful in N management but has little utility for P or K management in this crop system. Our results showed that K nutrient management guidelines are dated, further reducing VRA applicability.