Evaluation of a Fertilizer with Nitrification Inhibitor in Table Grape in Chile.

Nitrogen is the most important nutrient for table grape production; however its management is rather complicated as a shortage may cause yield losses while an excess may cause problems in fruit quality. Traditionally, large amounts of N as Urea (46%) have been used, with very low efficiency. The use of N fertilizers with nitrification inhibitor (NI) has the potential of improving N management in table grapes under drip irrigation. The present long-term study has for objective to determine the effects on N fertilization with NI on table grape var. Thompson Seedless, from plantation to production. The experimental layout corresponds to a randomized block design with four replications.  The following treatments are evaluated: four N rates; 0, 25, 50, and 100 % of the yearly maximum N rate, applied weekly as Novatec Solub 21 (21% N, with the NI 3,4- dimethylpyrazole phosphate, DMPP); two application frequencies at the maximum rate as Urea (46% N): weekly, and monthly; and Novatec Solub 21 at the maximum rate applied monthly.  Results have indicated that the fertilizer with NI allowed maintaining larger contents of available N during the season as compared with urea; plant vigor, expressed as pruning weight, increased with N rate when using NI, however no differences were observed at the maximum N rate when compared with Urea; N content in plant tissue increased with N application up to 50% of the maximum N rate, when using NI; similarly P content increased when using NI as compared to Urea; during the first harvest, table grape yields tended to increase with N rate, although no significant differences were found. Preliminary results suggest that when using Novatec Solub 21, the optimum N rate would be approximately 50% of the maximum N rate applied as urea