Avocado lubrication does not work well
Author: Ben Faber
Posted on: August 3, 2018
LTTLE PROOF TO SUPPORT THE USE OF APPLICATIONS
FOLIAR NUTRITIONS TO Simon Avett, Horticulturist Extension. Department of Primary Industries and Fisheries, Maroochy Research Station, Mayers Road, Nambour 4560, Queensland, Australia. Published in: Talking Avocados (published by Avocados Australia Ltd), 11 (2), 24-27.
The application of foliage fertilizers is sometimes promoted as an effective means of providing nutrients to the avocado. There are various products on the market as nutrients for avocados, some proponents even suggest that their products eliminate the need for nutrients applied to the soil. This article briefly reviews the literature on avocado foliage nutrition and examines the anatomy of avocado leaves and flowers in relation to nutrient intake.
Avocado Lubrication Spraying
The avocado leaf
The leaf structure of plants evolved primarily to capture sunlight and exchange gases, the roots evolved to absorb nutrients and water and anchor the plant. Any absorption of nutrients from leaves is therefore more likely to be more random than by design. In some crops the passive absorption of nutrients from the leaves is occasionally sufficient to supplement the supply of nutrients obtained from the roots. Most often this includes trace elements, which as their name suggests are required in very small quantities (eg copper and zinc). However, if immobile elements or elements with limited mobility in the plant (eg calcium, phosphorus, zinc, boron and iron) are discarded when foliage is sprayed, they are unlikely to reach the roots where they are also needed. Most nutrients will circulate free in the flow of water, but the movement of many is limited to the bark, so leaf applications do not meet the requirements of deficient trees. Occasionally large elements (such as nitrogen and potassium) are applied to compensate for a temporary deficit or to trigger a critical moment. Citrus fruits are an example of a crop where some of the nutrients applied to the foliage have been reported.
Avocado Lubrication Spraying: The ability of the leaf to absorb nutrients from its surface must depend to some extent on the permeability of its skin (outer layer) and the presence and density of the mouth (pores for gas exchange). Electron microscopic studies of ripe leaves and flowers in avocados show the presence of a waxy layer on both the top and bottom of ripe avocado leaves (Whiley et al, 1988). On the upper surface the wax appears as a continuous layer and there are no layers. On the lower surface the wax layer is spherical and there are layers. Blanke and Lovatt (1993) describe the avocado leaf as having a dense outer waxy cover in the form of rodents on young leaves and dendritic (branched) crystals on old leaves, including protective cells (guard cells surround the stamens). The flowers and sepals in avocados have layers on their lower surfaces and no layer of wax on either surface, which may explain why boron sprays may work.
Avocado lubrication Nitrogen spray
Based on the total leaf nitrogen concentration, Embleton and Jones (unpublished) in a repeated test in California in the early 1950’s found no response to urea leaf spray on ripe Fuerte avocado trees in the field. Up to three sprays per year were applied.
Nevin et al (1990) examined the fertilization of avocado urea foliage and found only one study (Aziz et al., 1975) that reported positive results in fruit yield. This test by Aziz et al (1975) included sprays with significant amounts of urea four times a year (250 to 500 g of nitrogen per tree per year). It is not clear if significant amounts of wetting spray reached the soil, however, the amounts applied were too high for foliar applications. No leaf analysis data were reported.
Galindo-Tovar (1983) was able to increase leaf nitrogen concentrations in “Hass” avocado plants grown in a greenhouse with low urea concentrations. However, similar treatments in the 3-year-old “Hass” in the field each month during the spring failed to increase leaf nitrogen in mature leaves sampled one week after spraying. The author cites data from crops other than avocados that suggest that urea can penetrate leaf surfaces when grown in a greenhouse, but when grown in the field under the sun, the leaf surfaces are different and resist nitrogen movement. on the sheet.
Klein & Zilkah (1986) reported significant urea-N leaf intake when “Fuerte” avocado leaves were extracted and immersed in urea solutions. Zilkah et al (1987) reported the displacement of 15N from the urea applied to foliage in plant and reproductive avocado sinks “Fuerte” and “Hass”. Despite the apparent response from Aziz et al in Egypt, Klein & Zilkah, and Zilkah et al in Israel, efforts at the University of California to demonstrate significant nitrogen uptake by foliar sprays were unsuccessful (Nevin et al., 1990). .
Research at the University of California, Riverside, found that the nitrogen content of Hass avocado leaves did not increase with the application of urea to foliage at the same concentration that doubled the nitrogen content of citrus leaves (Nevin et al., 1990). Maximum intake of 14C-urea from “Hass” avocado leaves was normally insignificant after 2 days. Over 96% of the applied 14C-urea was recovered from the leaf surface even after 5 days. The maximum intake of 14C-urea from “Gwen” and “Fuerte” leaves was less than 7%. 15N, 14C-urea and 65Zn are radioactive forms of nitrogen, urea and zinc respectively used to monitor their movement through the plant.
Sing and McNeil (1992) conducted a study in an orchard with a history of potassium deficiency, where high levels of magnesium in the soil competed with potassium for intake. Applications of 3.6% potassium nitrate foliage were applied at half leaf extension, full leaf growth and one month after full leaf swelling. These applications of potassium nitrate foliage were effective in increasing the potassium level in the leaves of “Hass” avocado trees, however it took two to three applications of foliage per year to achieve the same result with one application of potassium sulfate (strip) to the soil once every 2 up to 3 years. Calculating labor and materials costs, potassium nitrate foliar sprays were estimated to be more expensive than ground potassium sulfate applied every three years. Foliage sprays also affected the levels of other nutrients in the leaf, some negatively.
Calcium is considered as an element in avocado fruits that are associated with better quality and longer shelf life. Several different calcium products were tested in the 1980s as foliage spraying in South Africa in an effort to increase fruit calcium levels, but none were found to be effective.
Veldman (1983) reported that treatment of avocado trees with one, three, and six calcium nitrate sprays could not successfully control the point of pulp in avocado fruit, and there was no increase in fruit calcium levels in sprayed treatments.
Whiley et al (1997) report that calcium leaf sprays during fruit growth have little effect on internal concentrations in most fruits due to poor fruit absorption and lack of displacement within the tree.
Avocado lubrication spray with Boron
Some benefits have been reported from the application of boron foliage if applied during flowering. Synchronization is important because it seems that absorption takes place through flower structures and not leaves.
Jayanath and Lovatt (1995) reported the results of four flowering studies (two greenhouses and two field experiments) that showed the effectiveness of applying boron or urea spray to “Hass” avocado inflorescences during early expansion (cauliflower stage) but before full extension. of panic and flourishing. Anatomical analysis of the flowers provided evidence that pre-flowering boron spray increased the number of pollen tubes that reached the ovary and also increased ovarian viability, but to a lesser extent than urea. Prebloom urea spray increased ovarian viability compared to treated or untreated flowers. Urea also increased the number of pollen tubes that reached the ovary, but to a lesser extent than boron. However, the combination of boron and urea had a negative effect even when urea was applied 8 days after boron. the only treatment that had a positive effect on fertilization was boron in Year 2, the most likely reason why it did not Work in other years was considered low temperature. There were only hardened leaves that were present at the time of foliage application indicating that uptake was through flower sections.
Whiley et al (1996) report that despite the increase in fruit set by spraying boron foliage during flowering, there was no convincing evidence of increased final yield. Root growth requires boron and in deficient trees it is unlikely that sufficient nutrients from the foliage will be transferred to the roots. Foliage applications have the advantage that specific organs can be targeted to increase their boron concentrations, but with the disadvantage that insufficient boron can be absorbed through leaves to mediate chronic deficiency in trees. Soil applications have been shown to dramatically improve the health of boron-deficient trees.
Mans (1996) experimented with “Hass” trees that had nitrogen and boron levels in leaves below acceptable standards (N was 1.71% and B was 23 ppm). The aim of this experiment was to see if providing nutrients directly to the flowers could increase the yield of “Hass” trees growing in a cool environment. Mans (1996) found that if a multi-nutrient spray containing nitrogen and boron was applied as the first flowers began to open then it could increase the yield and size distribution of the fruit. The flowering stage during spraying was very important. Sprays applied before flowering, on fruit or when there was fruit were not effective.
Avocado lubrication spray with Iron
Kadman and Lahav (1971-1972) reported that the only means of controlling iron chlorine in already established avocado orchards was the application of iron chelates to the soil, as the applications of various foliar spray iron compounds were not commercially successful. Gregoriou et al (1983) found that the fastest and most successful treatment of trees suffering from iron chlorination in limestone soils was achieved by incorporating Sequestrene 138 Fe-EDDHA into the soil.
Avocado lubrication spray with Zinc
Kadman and Cohen (1977) found that avocado trees have difficulty absorbing minerals through their foliage. Nevertheless, spraying of zinc-deficient orchards was quite common in California and some other countries. In Israel, some growers spray their orchards, but experiments have shown no noticeable improvement in leaves or fruit after such treatment. The results presented in this paper show that the penetration of zinc into the leaves is so small that there is virtually no benefit in providing it with foliar sprays.
Zinc deficiency is common in avocados and is particularly difficult to treat in high pH (alkaline) soils. Crowley et al (1996) evaluated fertilization methods of “Hass” avocado trees in a two-year field experiment in a commercial orchard located on limestone soil (pH 7.8) in California. The methods of fertilization were:
• zinc sulfate applied to the soil or irrigation
• Zinc chelate applied to irrigation (Zn-EDTA)
• zinc nitrate trunk injection
• applications of zinc sulfate, zinc oxide or zinc metallic acid.
Among the three soil treatments and irrigation, zinc sulfate was applied at 3.2 kg per tree either as quarterly irrigation or annually as soil application was the most effective and increased the zinc concentrations in the leaf tissues to 75 and 90 mg / kg respectively. . Experiments with 65Zn applied to leaves of greenhouse seedlings showed that less than 1% of the zinc applied as zinc sulphate or zinc metal was actually taken up from the leaf tissue. There was also slight displacement of the zinc into sheet tissue next to the application points or to the sheets above or below the treated sheets. Given these problems with zinc foliage, Crowley et al (1996) suggest that fertilization using soil or irrigation with zinc sulfate may provide the most reliable method of correcting zinc deficiency in avocado and limestone.
Whiley and Pegg (1990) report that zinc foliage applications have been found to be extremely ineffective in Queensland orchards.
Price (1990) states that zinc can be absorbed through leaves (from foliar sprays, eg zinc sulfate, zinc chelate), but that insufficient zinc can be absorbed in this way to meet plant requirements, especially in avocados. Since zinc is required at the growing points of new roots and shoots, it is important that most of the zinc is absorbed by the roots.
Avocado Lubrication Spray – Sprays of Fungicides with Foliage
If the nutrient sprays applied to avocado leaves give inconsistent or zero effects, why do folic acid sprays work to control root rot? The amount of phosphoric acid intake required to control root rot is small, but nevertheless, several applications per year are required to be effective and the canopy must be dense and healthy. The phosphonate concentration required in the roots for effective control of root rot is 30 mg / kg. Achieving this level requires three to four sprays of 0.5% phosphoric acid per year at strategic times (Leonardi et al., 2000) or alternatively six or more 0.16% phosphoric acid sprays per year. Another factor that contributes to the effectiveness of phosphoric acid applied to leaves is that, unlike many nutrients, it is highly mobile to the plant.
Borys (1986) reports the distribution of dry root matter in shoots of avocado seedlings averaging 26% and 74%, respectively. Using these data and some critical levels of nutrients and fungicides in avocados we can get some perspective on the relative amounts required. In a tree consisting of about 100 kg of dry matter, about 26 kg would be at the roots and 74 kg at the shoots. This tree with a phosphonate root level of 30 mg / kg will contain a total of about 0.8 g of phosphonate in the roots. With optimal leaf levels of 50 mg / kg boron and 2.5% nitrogen, the tree would contain about 4 g and 1850 g of boron and nitrogen respectively in the canopy alone. From these relative amounts it appears that the fungicide required is substantially smaller than the nutrients.
Apart from timed boron applications during flowering in situations where leaf boron levels are inadequate, there is no clear evidence to support the use of foliar nutrient sprays in avocados to correct nutrient deficiencies or to provide nutrients for growth. Occasionally, a foliar nutrient spray may succeed in relieving the symptoms of leaf deficiency, however this type of application will not provide the long-term tree requirements for this nutrient that need to be addressed through soil applications.
I would like to thank Chris Searle and Tony Whiley and Garry Fullelove of the Queensland Gardening Institute for their help in writing this article. The literature search was performed using the AVOINFO avocado reference database.
Aziz, ABA, Desouki, I., El-Tanahy, MM, Abou-Aziz, AB and Tanahy, MM, El 1975. Effect of nitrogen fertilization on yield and avocado fruit oil content. Scientia Horticulturae, 3 (1): 89-94.
Blanke, MM and Lovatt, CJ 1993. Anatomy and transpiration of the avocado inflorescence. Annals of Botany, 71 (6): 543-547.
Borys, MW 1986. Root / shoot relationship and some root characteristics in avocado and Chinini plants. California Avocado Yearbook 70: 175-198.
Crowley, DE, Smith, W., Faber, B. and Manthey, JA 1996. Zinc lubrication from avocado trees. HortScience 31 (2): 224-229.
Galindo-Tovar, GE 1983. Effects of urea and surfactant concentration on avocados. MS Thesis, University of California, Riverside, USA. September.
Gregoriou, C., Papademetriou, M. and Christofides, L. 1983. Use of chelates to correct iron chlorination in avocados grown on limestone soil in Cyprus. California Avocado Annual Book 67: 115-122.
Jayanath, I. and Lovatt, CJ 1995. Efficacy studies in dome applications prior to boron and / or urea occurrence in Hass avocados, California. World Avocado Congress III, Proceedings: 181-184.
Kadman, A., and Lahav, E. 1971-1972. Experiments with various therapies for the treatment of avocado green trees. California Avocado Annual Book. 55: 176-178.
Kadman, A. and Cohen, A. 1977. Experiments with zinc applications in avocado trees. California Avocado Yearbook, 61: 81-85.
Klein, I. & Zilkah, S. 1986. Retention and urea uptake by avocados and apples. Plant nutrition. 9: 1415-1525.
Leonardi, J., Whiley, AW, Langdon, PW, Pegg, KG and Cheyne, J. 2000. Advances in the use of phosphonate foliar applications for the control of phytophthora root rot in avocados.
Mans, CC 1996. Effect of “Hass” foliage diet at different stages of flowering. Annual Association Book for South African Avocado Growers, 19: 31-32.
Nevin, JM, Lovatt, CJ and Embleton, TW 1990. Problems with avocado urea-N foliage fertilization. Acta Horticulturae 275: 535-541. International Symposium on the culture of subtropical and tropical fruits and crops. Vol. II. (JC Robinson, ed.), International Society of Phytosocial Sciences. Wageningen, The Netherlands.
Price, G. 1990. Are you thinking of faking your trees? Talking Avocados, Third Edition, Aug / Sept, p.5
Sing, JL and McNeil, RJ, 1992. The effectiveness of potassium leaf nitrate is sprayed on the avocado “Hass” (Persea americana Mill.), World Avocado II Conference, Proceedings: “The shape of the next things” (Lovatt, CJ ed.) 1: 337-342.
Veldman, G. 1983. Calcium nitrate is sprayed on avocados at the Westfalia Estate to reduce pulp. Annual Association Book for South African Avocado Growers, 6: 64-65.
Whiley, AW, Chapman, KR and Saranah, JB 1988. Water loss from flowering avocado structures (Persea americana cv. Fuerte) during flowering. Australian Journal of Agricultural Research, 39 (3): 457-467.
Whiley, AW and Pegg, KG1990. Correction of micronutrient deficiencies and control of Phytophthora root rot in avocados. Talking Avocados, Second Edition, May / June, p. 11.
Whiley, AW, Smith, TE, Saranah, JB and Wolstenholme, BN 1996. Avocado Boron Diet, Talking Avocados, 7 (2): 12-15.
Whiley, AW, Hofman, PJ and Coates, LM 1997. From Seed to Tray – Some Practices in the Field to Improve the Quality of Avocado Fruit. Proceedings of the Australian Avocado Growers Association and the New Zealand Avocado Association Association ’97, ‘Quality Search’. Rotorua, New Zealand, pp. 83-97.
Zilkah, S., Klein, I., Feigenbaum, S. and Weinbaum, SA 1987. Shift of 15N urea applied to foliage in reproductive and vegetable avocado sinks and its effect on the original fruit set. J. Amer. Soc. Hort. Science 112: 1061-1065.