Effect of Nitrogen Fertilizer Timing and Rate on Inorganic Nitrogen Status, Fruit Composition, and Yield of Grapevines

Abstract

A four-year (1987-90) trial was conducted to study the effects of timing and rate of N fertilizer application on furrow-irrigated Barbera, Grenache, French Colombard, and Chenin blanc grapevines. The objectives were to further determine optimum N fertilizer practices for important wine cultivars in the San Joaquin Valley and to compare inorganic N constituents, NO₃^--N and NH₄⁺-N, for N status determination. The six treatments included four N fertilizer application timings at budbreak (BB), fruit set (FS), veraison (V), and post-harvest (PH) with a 56 kg N/ha rate, as well as BB with a 2X rate of 112 kg N/ha and control (C0). Vine N status was determined by NO₃^--N and NH₄⁺-N levels and their sum, total inorganic N (TN), in bloom and veraison petioles. Yield and fruit composition parameters were measured for vine response. Cultivar responses varied widely, with Grenache and Barbera being the high and low extreme cultivars, respectively, in petiole TN status and responsiveness to N treatment; French Colombard and Chenin blanc were intermediate. Generally, TN status increased with increasing N rate (C0 • BB56 • BB112). Nitrogen fertilizer timing demonstrated that the more recent N applications often resulted in a higher petiole TN status at the next petiole sampling; i.e., PH56 and BB56 treatment petioles had higher TN status at bloom while FS56 was higher at veraison. Post-harvest timing was found to be particularly effective in supplying petiole TN in the spring; i.e., PH56 sometimes resulted in bloom petiole TN levels comparable to BB112 in all four cultivars and higher than BB56 in Grenache, French Colombard, and Chenin blanc. Petiole NO₃^--N levels were more sensitive than NH₄⁺-N levels to fertilizer treatment. The greater contribution of NO₃^--N to TN and their high correlation coefficients as compared to NH₄⁺-N and TN would place in question the utilization of NH₄⁺-N as an additional measurement of N status. Grape soluble solids was the most responsive fruit parameter to N treatment. Generally, N fertilizer decreased soluble solids over C0, irrespective of timing, and with the highest rate (112 kg N/ha) resulting in the largest decrease. Grape yields were only affected in Grenache, with all of the N treatments increasing yields over C0 except V56. This result, plus other negative effects of the V56 treatment, suggest that veraison was the least desirable timing of those compared. Otherwise, timing effects on fruit parameters were minor.