UNIVERSITY OF CALIFORNIA, RIVERSIDE. Botany. Department of. and. Plant Sciences.

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1 UNIVERSITY OF CALIFORNIA, RIVERSIDE Department of Botany and Plant Sciences

2 $ Fertilizing the Hass $ Avocado for Maximum Profitability $ $ Carol Lovatt Professor of Plant Physiology University of California-Riverside $ $ $ carol.lovatt@ucr.edu

3 Fertilizing $ the Hass Avocado $ $ 1) An overview of fertilization. $ $ $ 2) Fertilizer best management practices make dollars and sense. 3) Can we fertilize our way out of alternate bearing? $

4 Fertilizing the Hass avocado Optimizing fertilization of the Hass avocado is a cost-effective strategy for increasing yield and profitability. In California, despite four decades of research, only a limited number of experiments have been conducted to determine optimal rates of soilapplied fertilizers - N, P, K, Fe, and Zn.

5 Problems All other fertilizer recommendations are based on leaf analyses using optimum ranges borrowed from citrus and, though modified over the years, are not related to any avocado yield parameter. Avocado leaf analyses do not detect differences in tree nutrient status or fertilization rates related to yield.

6 Problems Leaves for nutrient analysis are collected in August-September, which is too late to correct deficiencies that negatively impact the current crop. Avocado leaf analyses were developed to guide replacement fertilization for the next year s crop; careful management is required to prevent under-fertilization of ON-crop trees and over-fertilization of OFF-crop trees!

7 Fertilizer Best Management Practices (BMPs) A demand-driven fertilization strategy matches fertilizer rates and application times to meet the nutrient demand of the different stages of avocado tree phenology, increases fertilizer-use efficiency is cost-effective and environmentally friendly.

8 Our Approach Identify the role essential nutrients play in the physiology of the crop, Apply the nutrient as a foliar or soil fertilizer at a key stage in the phenology of the tree when nutrient demand is high to stimulate a specific metabolic process that results in increased yield, fruit size or quality and a net grower profit.

9 An overview of fertilization of Hass avocado trees

10 An overview of fertilization of Hass avocado trees

11 An overview of fertilization of Hass avocado trees X X

12 An overview of fertilization of Hass avocado trees

13 An overview of fertilization of Hass avocado trees 2x N in April or November significantly increased total yield, yield of commercially valuable fruit and reduced alternate bearing

14 An overview of fertilization of Hass avocado trees XX X XX X 2x N in January, February or June had no effect on yield, fruit size or alternate bearing, thus there is no need to add extra N at these times

15 An overview of fertilization of Hass avocado trees 1x N or N-P-K in July and August significantly increased total yield and yield of commercially valuable fruit compared trees that did not receive N or N-P-K in both July and August

16 An overview of fertilization of Hass avocado trees X X 1x N-P-K applied four times (April, July, August, November) or 2x N-P-K in April or November reduced total yield and yield of commercially valuable fruit

17 Fruit Dry Wt (g/fruit) Total Flesh Peel Seed Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

18 Nitrogen content of Hass avocado fruit Fruit N content (mg/fruit) Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Each point is the mean between 5 and 12 fruit, with standard error bars.

19 Potassium content of Hass avocado fruit B. Fruit K content (mg/fruit) Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Each point is the mean between 5 and 12 fruit, with standard error bars.

20 Calcium content of Hass avocado fruit. Fruit Ca content (mg/fruit) C. 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Each point is the mean between 5 and 12 fruit, with standard error bars.

21 Mineral balance (g per tree) of 20-year-old Hass avocado in California. Proportion Leaves removed & twigs Branches Trunk Roots Fruit Total by fruit (%) N P K Ca Mg S Al B Fe Mn Na Zn

22 Fertilizer BMPs make dollar$ and sense Shoot K Fruit Ca + K Root N, K, Ca, Fe + Zn Fruit K

23 Fertilizer BMPs make dollar$ and sense Matching fertilizer rates and application times to meet the nutrient demand of different stages of avocado tree phenology makes sense based on tree physiology fertilizer-use efficiency cost to benefit protection of the environment.

24 Can we fertilize our way our of alternate? Our understanding of best management practices in an alternate bearing Hass avocado orchard would definitely benefit from additional research. There are fertilizer practices with known benefits that should be considered.

25 1.3 lbs B/acre (6.3 lbs Solubor/acre; 20.5% B) 23 lbs N/acre (50 lbs urea/acre; 46% N, 0.25% biuret) Boron increased yield 12,125 lbs/acre/3 yrs Urea increased yield 10,913 lbs/acre/3 yrs

26 Can we fertilize our way out of alternate bearing?

27 Can we fertilize our way out of alternate bearing? Periods of N uptake by Hass avocado trees

28 Can we fertilize our way out of alternate bearing?

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30 Can we fertilizer our way out of alternate bearing? Since fruit number drives the uptake of many essential nutrients, matching fertilizer rates and application times to periods of high nutrient demand by the fruit to periods of strong canopy growth (floral and vegetative) is a solid approach to maximizing yield with the potential to mitigate alternate bearing.

31 Maximize Hass Tree Physiology 1. Maintain healthy roots (uptake of water and nutrients) and leaves (energy production). 2. Maintain balance between leaf number and fruit number for large size fruit. 3. Maintain balance between shoot number and fruit number to reduce alternate bearing (prune early in the on-crop year). 4. Fertilize the current crop load, includes both setting and maturing fruit; do not fertilize to replace what the previous crop used. 5. If possible, harvest earlier rather than later.

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