The 2012 ASHS Annual Conference

Our previous research has demonstrated the potential of crop forcing to shift fruit ripening to the cooler portion of the growing season and to improve fruit quality of wine grapes in warm regions. When a large portion of the new growth was removed for forcing, petiole NO₃-N content at full bloom was deficient in forced vines while the contents of other mineral nutrients remained within normal range. Furthermore, lower vine vigor and yield were observed in forced vines, compared to non-forced vines in previous experiments. An experiment was conducted in a mature Cabernet Sauvignon vineyard in the San Joaquin Valley of California to determine if vine N status, vigor, and yield of forced vines can be improved by supplemental N applications. UN-32 liquid fertilizer was applied under drip irrigation emitters at 28 kg N/ha four times at 14 d intervals before or after forcing, starting four weeks prior to full bloom of non-forced vines or three weeks prior to full bloom of forced vines. Forcing was conducted on 24 June 2011, when growing shoots were hedged to six nodes and all leaves, summer laterals, and primary clusters were removed. N applications did not affect the number of forced shoots and clusters but resulted in greater vine vigor and higher yield. Petiole NO₃-N content at full bloom was increased markedly by N applications, more so when N was applied after forcing. Petiole total N content was increased by N applications before and after forcing at a similar magnitude. The content of other mineral nutrients at full bloom affected by N applications included lower P and Zn by N applications before and more so after forcing; higher Mn only by N application before forcing; and higher Ca and Mg only by N application after forcing. Analysis conducted at veraison for non-N and N application after forcing revealed higher NO₃-N, total N, Mn, and Ca but lower P, B, and Cu with N application. Only NO₃-N was deficient in forced vines without N application, limiting vine growth and cropping. N application after forcing was more effective, improving vine N status as well as increasing vine vigor and yield.