TY - JOUR T1 - Recovery of <sup>15</sup>N-labeled Fertilizer by Thompson Seedless Grapevines: Effects of N Fertilizer Type and Irrigation Method JF - American Journal of Enology and Viticulture JO - Am. J. Enol. Vitic. SP - 509 LP - 517 DO - 10.5344/ajev.2015.14115 VL - 66 IS - 4 AU - Larry E. Williams Y1 - 2015/11/01 UR - http://www.ajevonline.org/content/66/4/509.abstract N2 - A study was conducted to determine the N fertilizer recovery efficiency (REN) of Vitis vinifera L. cv. Thompson Seedless grown in the San Joaquin Valley of California. Vines were drip- or furrow-irrigated and fertilized with 15N-labeled potassium nitrate (KNO3) or ammonium sulfate (NH4)2SO4. The fertilizers were applied shortly after anthesis with a single application of 25 g N/vine (~28 kg N/ha). An additional set of the drip-irrigated vines was fertilized 10 times beginning 20 April across a 20-week period during the growing season with labeled KNO3 (amounts equivalent to ~31 kg N/ha). Total biomass, N concentrations, and 15N of all vine organs, including the root system, were measured. There were no significant differences in REN (~40%) between the two fertilizer types (nitrate versus ammonium) for the drip-irrigated vines or for the comparison of a single application of KNO3 to a split application of that fertilizer applied every two weeks. The REN of furrow-irrigated vines was ~12%. The partitioning of 15N-labeled fertilizer taken up by the vine was significantly affected by fertilizer treatment. Approximately 47% of the ammonium fertilizer for the drip-irrigated vines was found in the clusters, while only 30% of the nitrate fertilizer for the split application of the fertilized, drip-irrigated vines was found in the clusters. The greatest amount of fertilizer N found in the roots was for the nitrate fertilized vines under drip-irrigation (both single and split applications). The results indicated that irrigation type greatly affected REN of the N fertilizers used in the study, and that irrigation and fertilizer type affected the distribution of N once it was taken up by the vine. ER -