Nitrogen requirements of table grape cultivars grown in the san Joaquin valley of California

Abstract

Context and purpose of the study ‐ Ground water in the interior valleys of California is contaminated with nitrates derived from agricultural activities, primarily the over-fertilization of crops. Agriculture is now mandated by the State of California to monitor all possible nitrogen (N) inputs into agro‐ecosystems and only apply N amounts that meet a crop’s demand. The best estimate of N required for the current season’s growth of shoots and fruit in raisin, table and wine grape vineyards in the San Joaquin Valley is approximately 70 to 80 kg N ha‐1 (values derived from Thompson Seedless and several wine grape cultivars). The table grape industry continues to develop new cultivars and replanting vineyards using open‐gable trellis systems which will produce greater vegetative biomass and fruit yields. One objective of this study was to determine the N budget of several established and newer table grape cultivars trained to overhead trellises, grown in the San Joaquin Valley.

Materials and Methods – Flame Seedless, Scarlet Royal, Crimson Seedless, Princess, Sheegene‐21 and Autumn King grapevines grown at eight commercial vineyards within 30 km of the KARE Center were used in the study. N fertilizer was applied in three of the vineyards, the amount being that removed in the fruit at harvest and twice that. The control vines received no applied N. Petioles were collected at bloom and veraison to assess vine N status. Shoots and clusters were removed from data vines in each vineyard at bloom, veraison and fruit harvest, biomass and N concentrations determined and N budgets developed in each vineyard.

Results ‐ Petiole nitrate‐N at bloom and veraison were significantly correlated with petiole ammonia‐N and total N measured at the same stage and total N in the leaves, stems and fruit at bloom, veraison and harvest. Values of petiole nitrate‐N below 200 ppm (dry weight basis) at bloom in the current season resulted in fewer clusters produced by the vines the following year. Yield of Flame Seedless, Scarlet Royal and Crimson Seedless averaged across treatments and years was 55, 67 and 53 t/ha, respectively. The amount of N per ton of fruit ranged from 0.98 to 1.85 kg. The amount of N accumulated by vines at harvest in the leaves, stems and clusters ranged from 131 to 210 kg/ha. The amount of N in the fruit (kg/t) was dependent upon location and somewhat correlated with petiole analyses at bloom and veraison.The amount of N to produce a crop was a function of location, row spacing and supply of N from the irrigation water and soil profile. The N required by the vines in these table grape vineyards were much greater than earlier estimates.