Effect of alternative irrigation strategies on yield and quality of Fiesta raisin grapes grown in California

Authors: ABRISQUETA, ISABEL - Centro De Edafologia Y Biologia Aplicada Del Segura (CEBAS); Ayars, James

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2018
Publication Date: 4/30/2018
Citation: Abrisqueta, I., Ayars, J.E. 2018. Effect of alternative irrigation strategies on yield and quality of Fiesta raisin grapes grown in California. Water. 10:583. https://doi:10.3390/w10050583.
DOI: https://doi.org/10.3390/w10050583

Interpretive Summary: As the competition for water increases, agriculture will have to develop methods to extend the existing water supply while maintaining production. This is true during periods of drought as well. During droughts a decision can be made to not plant annual crops, however, this alternative does not exist for perennial crops. One alternative for perennial crops is deficit irrigation during select periods that will minimize the impact on yield. Table and raisin grapes have not traditionally been deficit irrigated but in the future it may be necessary during periods of extended drought and limited water supply. We developed a project to look at 2 deficit irrigation strategies on Fiesta raisins based on the grower practice that was deemed fully irrigated. We found that the yields were maintained and improved compared to the grower practice with up to a 30% reduction in applied water when rainfall was included in the total water supply. Rainfall should be included in any water management strategy. We concluded that it is possible to deficit irrigate raisins without any negative effects on yield. The reduction in applied water will result in reduced operating costs since the water supply was a pumped well.

Technical Abstract: Raisins and table grapes are not typically candidates for deficit irrigation, however, with the potential for drought and the competition for water in California, we felt it was necessary to evaluate alternative irrigation strategies to determine if deficit irrigation was an alternative. We established a replicated trial with 3 irrigation treatments and 3 replications on a farmer's field. We had 2 deficit treatments plus the grower practice (GP) and used the GP as the fully irrigated treatment. We designed the remaining treatments as a percentage of the GP with different reductions based on the plant physiology. The GP fully irrigates the vines until just before the canes are cut in August at which time irrigation is halted until after harvest when it is resumed until the end of October. Treatment 2 follows the same irrigation pattern with the applied water being equal to 80% of the grower practice. This was done by reducing the time of irrigation. Treatment 3 irrigates at 50% of the grower practice until fruit set at which time the irrigation is increased to 80% of GP until cutoff prior to harvest. The treatment resumes at 50% of GP for the month of October following harvest. The crop was drip irrigated with 2 L/hr emitters spaced 1 m apart along the lateral. Irrigations were done weekly for approximately 56 hrs from Friday evening to Monday afternoon. The crop was Fiesta raisins on a continuous tray. The row spacing was 3.6 m and the in-row plant spacing was 2.1 m. Each plot consisted of 3 rows with the center row being the experimental row. Data was taken from 10 vines within the row. Applied water was measured with flow meters on each treatment, and soil water was monitored with capacitance probes. The irrigation was controlled with a datalogger that also recorded flow data. We measured the yield and quality of the grapes as well as the pruning weights. The total applied water including rainfall over the 3 years of the study ranged from 1044 mm to 533 mm. The applied water in 2014 was the lowest in each of the years due to the drought and concerns for the well operation. The yields were highest in 2014 with the lowest applied water. The deficit treatments had yields equal to or better than the grower practice in each year. The quality was not affected by deficit irrigation. For this type of trellis (2 wire T) approximately 550 mm is adequate for producing good yields. It will also result in improved returns due to a reduction in pumping costs.