Optimal Nutrient Concentration Ranges of ‘Hass’ Avocado Cauliflower Stage Inflorescences—Potential Diagnostic Tool to Optimize Tree Nutrient Status and Increase Yield

Abstract

<jats:p>Optimizing ‘Hass’ avocado (<jats:italic>Persea americana</jats:italic> Mill.) tree nutrient status is essential for maximizing productivity. Leaf nutrient analysis is used to guide avocado fertilization to maintain tree nutrition. The goal of this research was to identify a ‘Hass’ avocado tissue with nutrient concentrations predictive of yields greater than 40 kg of fruit per tree. This threshold was specified to assist the California avocado industry to increase yields to ≈11,200 kg·ha<jats:sup>−1</jats:sup>. Nutrient concentrations of cauliflower stage inflorescences (CSI) collected in March proved better predictors of yield than inflorescences collected at full bloom (FBI) in April, fruit pedicels (FP) collected at five different stages of avocado tree phenology from the end of fruit set in June through April the following spring when mature fruit enter a second period of exponential growth, or 6-month-old spring flush leaves (LF) from nonbearing vegetative shoots collected in September (California avocado industry standard). For CSI tissue, concentrations of seven nutrients, nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), sulfur (S), zinc (Zn), and copper (Cu) were predictive of trees producing greater than 40 kg of fruit annually. Conditional quantile sampling and frequency analysis were used to identify optimum nutrient concentration ranges (ONCR) for each nutrient. Optimum ratios between nutrient concentrations and yields greater than 40 kg per tree were also derived. The high nutrient concentrations characterizing CSI tissue suggest current fertilization practices (timing or amounts) might be causing nutrient imbalances at this stage of avocado tree phenology that are limiting productivity, a possibility that warrants further investigation. Because CSI samples can be collected 4–6 weeks before full bloom, nutritional problems can be addressed before they affect flower retention and fruit set to increase current crop yield, fruit size, and quality. Thus, CSI nutrient analysis warrants further research as a potential supplemental or alternative tool for diagnosing ‘Hass’ avocado tree nutrient status and increasing yield.</jats:p>

The Significance of Macronutrients in Alternate Bearing ‘Nadorcott’ Mandarin Trees

“…These results question the pertinence of current nutritional guidelines or leaf mineral nutrient norms that are used for 'Nadorcott' mandarin orchards in an alternate bearing cycle in South Africa, where the purpose of fertilization should be different during an ''on'' vs. an ''off'' season in terms of manipulating vegetative shoot flush, flowering, and fruit load (Stander et al, 2018). Similar to what has been reported for avocado (Persea americana) (Campisi-Pinto et al, 2017), it could be possible that leaf analysis is not sensitive enough to detect changes in macronutrient status of 'Nadorcott' mandarin trees, or differences in fertilization rates that may affect fruit load or result in the manifestation of alternate bearing. For example, in other evergreen fruit trees such as avocado, coffee (Coffea arabica), and olive (Olea europaea), organs such as flowers, petioles of leaves, and stems of flowers and fruit are alternative tree organs from which nutrient analyses provide valuable supplemental information to leaf nutrient analyses (Campisi-Pinto et al, 2017;Castillo-Gonzalez et al, 2000;Khelil et al, 2010;Martinez et al, 2003;Razeto and Salgado, 2004).…”

“…Similar to what has been reported for avocado (Persea americana) (Campisi-Pinto et al, 2017), it could be possible that leaf analysis is not sensitive enough to detect changes in macronutrient status of 'Nadorcott' mandarin trees, or differences in fertilization rates that may affect fruit load or result in the manifestation of alternate bearing. For example, in other evergreen fruit trees such as avocado, coffee (Coffea arabica), and olive (Olea europaea), organs such as flowers, petioles of leaves, and stems of flowers and fruit are alternative tree organs from which nutrient analyses provide valuable supplemental information to leaf nutrient analyses (Campisi-Pinto et al, 2017;Castillo-Gonzalez et al, 2000;Khelil et al, 2010;Martinez et al, 2003;Razeto and Salgado, 2004). Indeed, studies on mineral nutrients and alternate bearing in other mandarin cultivars, e.g., 'Kinnow' (Mirsoleimani et al, 2014) and 'Michal', 'Wilking', and 'Murcott' (Monselise et al, 1983), have shown that the effects of fruit load in the current season on bud responses in the following season are also closely related to the nutrient concentration in stems.…”

Macronutrient dynamics in avocado (Persea americana Mill.) ‘Hass’ under the central peruvian coast conditions

“…in fruits that the concentration of the nutrient increases from flowering to early fruit set, and then decreases in fruit growth. Campisi et al (2017), found that P increased as inflorescence development progressed.Additionally, they mention that during the cauliflower phase were found valueshigher than those for full flowering, and the latter even exceeded those found in developing fruits (Campisi et al, 2017). Studies in cowpea obtained similar results regards to the P increase at flowering stage and at the beginning of pod formation (Suzuki et al,2021).…”

“…The variation of total N remained stable throughout the phenology, like values reported by Figueroa et al (2001). Campisi et al (2017) mentioned that optimal ranges of N in cauliflower inflorescences of 'Hass' vary from 2.7 % to 3 %. In our case, the concentration of 2.7 % was obtained.…”

“…K in fruits was higher at flowering and fruit set, but an opposite behavior occurred at stages 4, 5 and 7. The concentration of K in the cauliflower stage ranged from 1.4 % to 1.7 % (Campisi et al, 2017). However, samples for fruit analysis were taken from peduncles of completely differentiated, unopened flowers, in which a concentration of 2.22 % was found.…”