NITROGEN ACCUMULATION AND FERTILIZER USE EFFICIENCY BY GRAPEVINES IN SHORT-SEASON GROWING AREAS

Mature 'Concord' vines (Vitis labrusca L.) were excavated at 2- to 4-week intervals through the season to study seasonal changes in vine N concentration. Vine N content began increasing 2 weeks after budbreak, increased most rapidly from mid-May to mid-July, and declined between fruit maturation and the beginning of leaf senescence, Vine N content was lowest at budbreak (18 g) and maximum at fruit maturity (75 g). This change represented a net accumulation of 57 g N/vine or 77 kg N/ha, In a separate study, 'Seyval blanc' vines were treated with double N-15-labeled ammonium nitrate at either budbreak or bloom. Labeled N was applied as a spray beneath vines to simulate a broadcast vineyard application. Vines were excavated when leaves began to senesce in October, partitioned into various components, and analyzed by mass spectrophotometry to determine fertilizer-derived N content. Vines had recovered statistically similar percentages of fertilizer N applied at budbreak (7.1%) and bloom (10.6%), The low recovery of fertilizer N likely resulted from the method of fertilizer application, the presence of a competitive grass sod between the rows, and relatively high native soil N levels.