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Trellis, rootstock, and nitrogen effects on Sunpreme, a natural dry-on-vine raisin grape variety | OENO One
From 2021 to 2023, the effects of trellis type (two-wire “T” versus high single wire), rootstock (own-rooted, Freedom, or 1103P), and annual nitrogen fertilizer application rate (40 versus 80 lbs N/acre) were evaluated in the San Joaquin Valley to determine impacts on Sunpreme productivity, raisin quality and mineral nutrition. The T-trellis increased yield approximately 10%, with a slight decrease in raisin quality, compared to the high single-wire trellis. Rootstocks also increased yield by 10%. The higher N rate did not increase raisin yield, but it reduced raisin quality. None of the treatments tested affected preharvest fruit drop. Petiole and blade nutrient concentrations were affected to some extent by all treatments, but most nutrients, other than potassium (K) and zinc (Zn), were present at concentrations that are generally considered adequate. Vine nutrition was particularly affected by rootstock, with vines on Freedom having the highest levels of boron (B), potassium (K), and nitrogen (TN), and the lowest Zn Vines on 1103P had the lowest K and highest magnesium (Mg). Own-rooted vines had the lowest NO3-N, Ca, and Mg, but the highest Zn. Effects of rootstocks on nutrition could have management implications, depending on soil type. The amount of select nutrients in 1 t of raisins was determined. There were approximately 0.0089 kg B, 7.3 kg K, 0.345 kg Mg, 5.8 kg N, and 0.0025 kg Zn in a t of raisins. The quantity of certain nutrients in raisins was most affected by rootstock. Vines on Freedom had the most B and K, and among the most Mg and N. Increasing the N application rate modestly increased yield, and the harvested raisins contained approximately 44.8 to 58.3 kg N/ha, depending on N rate. These values provide practical estimates for nutrient replacement in NDOV vineyards. Overall, yield improvements were achieved with two-wire trellis and rootstocks, while higher N rates increased yield at the expense of quality. Annual applications of 44.8 – 56 kg N per hectare appear sufficient to sustain yield and maintain raisin quality.
