Author

Minh LeFollow

Date of Award

12-2020

Degree Name

MS in Agriculture - Crop Science

Department/Program

Horticulture and Crop Science

College

College of Agriculture, Food, and Environmental Sciences

Advisor

Lauren Garner

Advisor Department

Horticulture and Crop Science

Advisor College

College of Agriculture, Food, and Environmental Sciences

Abstract

Fruit tree leaf nutrient concentrations are commonly used to determine fertilizer rates, but information is limited regarding nutrient requirements, seasonal N uptake and removal rates, and soil N dynamics for pomegranate. Relationships between fertilizer rates, leaf nutrient concentrations, fruit yield and quality were examined in five mature, commercial California ‘Wonderful’ pomegranate orchards. Site 1 was observed for two growing seasons (2018-2019) and sites 2-5 were observed for one season (2018 or 2019). In 2018, 150, 300, or 450 g N/tree was applied at sites 1-3 in a single application at early fruit development or in two equal applications at early and mid-season fruit development. In 2019, fertilizer rates were adjusted based on site-specific leaf nutrient analysis and crop load and applied at mid-season fruit development (158, 185, 225, 286, 392, or 625 g N/tree at site 1; 115, 130, 150, 175, 212, or 270 g N/tree at site 4; and 107, 122, 142, 171, 214, or 286 g N/tree at site 5). A randomized complete block design was used for all experiments. Leaves were collected from all data trees during early, mid-season and late fruit development and analyzed for leaf nutrient concentrations. At harvest, total fruit weight per tree and individual fruit weight and diameter were measured. Canopy volume was measured during the dormant season prior to pruning. Nitrogen partitioning, uptake and removal rates were studied by analyzing plant tissue, soil, and lysimeter water samples in 2019 at site 5. Fruit yield and average diameter varied significantly depending on site and fertilizer treatments. Average fruit yield per tree ranged from 5-90 kg fruit/tree (site 1: 78.5 kg fruit/tree in 2018 and 91.1 kg fruit/tree in 2019, site 2: 55.6 kg fruit/tree, site 3: 29.7 kg fruit/tree, site 4: 5.6 kg fruit/tree, site 5: 9.1 kg fruit/tree). Sufficiency ranges and significant relationships were determined between certain nutrients, including nitrogen and potassium, to fruit yield and diameter. Higher fertilizer treatments were associated with higher residual soil N compared to the low fertilizer treatments within the root zone (2.25-19.33 mg/L NO3-N) and below the root zone (2.25-9.17 mg/L NO3-N) suggesting a higher likeliness of nitrogen leaching with fertilizer applications exceeding the crop’s nitrogen demand. Overall, variability between sites in fertilizer treatment effects, leaf nitrogen concentrations, and yield suggests that setting site-specific yield goals based on estimated N uptake and removal is necessary to develop effective pomegranate fertilizer programs.

Available for download on Monday, December 11, 2023

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