Effect of nitrogen fertilization on growth, canopy density, and yield of Vitis vinifera L. cv. Cabernet Sauvignon

The effect of nitrogen supply on the vegetative and reproductive capacity of vines of low nitrogen status was investigated in a field trial conducted in Western Australia. Five rates of nitrogen fertilizer (0, 50, 100, 200, and 400 g N/vine) were applied to irrigated, 12-year-old Cabernet Sauvignon vines over three seasons. Two-thirds of the nitrogen was applied late budbreak and the rest at two weeks after flowering. Moderate rates of nitrogen fertilization stimulated vine growth and vigor (shoot extension rate) resulting in an increase in canopy density. Prior to flowering, maximum vine vigor was observed upon addition of 100 g N/vine, This effect was no longer evident after flowering. Those vines supplemented with 100 g of nitrogen also achieved maximum petiole nitrate concentrations at flowering, growth (shoot length, pruning weight, and leaf area), and canopy density (leaf layer number), Vines receiving 400 g N/vine had shorter shoots and less pruning weight than vines receiving 100 g N/vine, as vigor did not respond to nitrogen fertilizer prior to flowering. However, the petiole nitrate concentration, total leaf area, and canopy density of vines supplied with 200 to 400 g N/vine were no different to those vines supplemented with 100 g N/vine. Nitrogen had no effect on the total vine yield in the first and last season. However, the highest yield came from vines receiving 100 g N/vine in the second season. Additional applications of 200 g and 400 g N/vine increased the yield no further. Higher berry numbers per bunch were associated with the increase in total vine yield. It appeared that moderate rates of nitrogen fertilization can have a beneficial effect on vine productivity in situations where vine nitrogen status is low. In contrast, excessive nitrogen fertilization was an unprofitable exercise as it provided no further benefits in terms of vine productivity.