Why apply nutrients in the Fall?
Plants need light, carbon dioxide (CO2), water (H2O), and minerals for their development, growth, and for producing quality fruit (Marschner 2002). Most nutrient uptake occurs through the roots, between bloom and the rapid vegetative growth phase. In most perennial tree fruit, however, initial Spring growth and early fruit development rely mainly on reserves accumulated the previous season (Weinbaum et al., 1984). There is evidence that Fall applications of nutrients can help in building up reserves for the subsequent year´s critical early growth (Nielsen et al 1996; Lang 2005).
The macronutrients nitrogen (N), potassium (K), phosphorous (P), calcium (Ca), magnesium (Mg) and sulfur (S), should always be managed through the soil, unless there are absorption problems such as poor root volume or alkalinity. Micronutrients, on the other hand, can be managed effectively and efficiently with foliar sprays, especially under low or high soil pH (below 6.0 and above 7.5), coarse texture soils (sandy or gravely soils), and if needed early in the season when root uptake is low. Foliar applications of micronutrients are effective, however, keeping their level in the soil within adequate levels is always beneficial for root growth and tree health.
Fall nutrient sprays can be utilized for different purposes; to ensure adequate reserves for following season, to manage vigor and return bloom or for disease control. So, before one decides to spray nutrients or not, is important to define your goal. In the following I provide a few examples and things to consider.
Fall sprays to build reserves and overall nutrient management
Fall sprays are recommended for nutrients that are mobile in the plant and can be stored for the following season, or nutrients that are needed early in the spring when root uptake is not efficient (Fageria et al., 2009). Fall sprays will be positive and effective only when the trees are deficient for that particular nutrient. Under adequate nutrient condition, foliar sprays are ineffective (Wojcik and Morgas 2013) and can also lead to toxicity.
Orchard deficiency can be predicted with leaf tissue analyses during summer (http://treefruit.wsu.edu/leaf-tissue-analysis)and visual analyses of symptoms. Some metals have characteristic symptoms (Figure 1), however if your soils are alkaline, calcareous or with pH above 7.5, you most certainty will need Zn on a frequent basis.
Nitrogen is the only macronutrient that has been recommended for fall sprays because it can be stored and remobilized during early development. Nitrogen and carbohydrate reserves are the main source for initial growth and early fruit development in most tree fruit species, most importantly in fruit that have short and early development or in those where pollination happens before leaves are fully expanded such as cherries, apricots, peaches, nectarines, apples and pears (Nielsen et al. 1996; Lang, 2005).
Leaf tissue analyses obtained during the summer, combined with assessment of the overall tree vigor are the best indicators for nitrogen deficiency (Righetti et al. 1998). Fall nitrogen sprays have also been suggested when the trees were cropped heavily and appear weak after harvest.
Micronutrients. Among the micronutrients, boron (B) and zinc (Zn) are most frequently recommended for fall application. Deficiency of both nutrient have been reported widely in the PNW region due to extensive areas with high soil pH and sandy soils (Nielsen et al. 2004, Peryea et al, 2003). Boron is needed early in the season for new growth; root and shoot tips, pollen tube growth and fruit set (Wojcik and Wojcik 2006) and early fruit development and quality (Cheng and Raba, 2009). Fall applications can increase boron content when deficient, for early spring growth. However, Peryea et al. (2003), reported that boron maintenance sprays in apples and pears are more effective at pink flowering stage and mentioned that postharvest sprays haven’t been widely adopted in apples due to logistics and efficacy in later harvest dates.
Zinc, also has low mobility in plants and it is needed early in the season for carbohydrate metabolism, fertility and seed production. Deficiency can be easily observed in younger leaves with interveinal chlorosis and shortened internodes, most frequently in cold, wet soils, or in soil with a high pH (above 7.5), where Zn becomes unavailable. Fall and dormant sprays have alleviated Zn deficiencies in tree fruit (Nielsen and Nielsen 1994).
For leaf nutrient sprays, mixing micronutrients with urea have shown improved uptake (Fernandez et al. 2013; Sanchez and Righetti 2005).
Table 1. General fall recommendation for tree fruit under diagnosed deficiency.
|Boron||Sodium borate||1 to 1.6 lb of B.
Boron is not suggested to nonbearing trees.
|8 – 10 lb of Zn for apples and cherries.
3 lb of Zn for peach and nectarine.
For nonbearing trees apply 0.5 lb.
|8 – 10 lb of N. When using Urea make sure has less than 0.25% biuret.|
|Note: For nutrients containing sulfate (example; Zn sulfate), wait until temperatures are below 80 º Fahrenheit.
1 Pounds of actual element in 100 gallons of water per acre.
There are several formulations for each nutrient. The most common formulations are listed in Table 1. Whatever the source, always check the label recommendation. To calculate the amount of product based on the actual amount needed, divide the actual amount recommended by the percentage of the element indicated in the label.
Example: Urea (46% of N) = If you need to apply 8 lbs./acre. Then 8 / (46%) = 17 lbs. of Urea.
Fall nutrient spray should be done when growth has ceased as it can increase danger of winter freeze damage when promoting new growth (Righetti et al. 1998), but before natural leaf fall (green leaf), to ensure absorption and remobilization to the roots.
Fall sprays to manage vigor and return bloom
If you have excess vigor in your orchard, avoid nitrogen during the fall. On the contrary, if you need more vigor in your orchard, fall nitrogen can help develop reserves. Nitrogen deficiency have also been associated with inducing biennial bearing. If you are in your “off year” and you expect higher cropping the following year, fall nitrogen can increase vegetative to fruit relation, and vice versa, when expecting low crop, avoid fall nitrogen.
For disease prevention
Some fall nutrient sprays can help prevent fungal diseases. Copper (Cu), for example it is utilized as a fungicide although is application can also help if the copper is deficient.
Fall sprays of urea have also been utilized to induce leaf drop. The concentration should be higher than that used as a fertilizer. For example, urea at 5% has been utilized to reduce inoculum of Venturia inaequalisresponsible for apple scab (Qazi et al. 2005).
The effect of high rates of urea, in some cases also combined with zinc sulfate, seems to be associated more to a toxic effect, which induces leaf drop earlier in the season, before cold or rain can increase the probability of the infection through the leaf scar. Ouzounis and Lang (2005) also indicated that urea spray for early defoliation improved cold acclimation in cherries.
- Fall sprays are beneficial and effective only when the trees are deficient for that particular nutrient.
- Fall nitrogen applications can help in building up reserves for the subsequent year´s critical early growth.
- Fall zinc and boron spray can benefit reproduction and early fruit development.
- Fall spray should be done when growth has ceased but before natural leaf fall.
For more information:
Sallato, 2018. Leaf tissue analysis. Fruit Matters. http://treefruit.wsu.edu/leaf-tissue-analysis
WSU Tree Fruit Extension
Cheng, L. and R. Raba. 2009. Nutrient Requirement of Gala/M.26 Apple tree for high yield and quality. Cornell University.
Fageria N.K., M.P. Barbosa Filho , A. Moreira and C. M. Guimarães. 2009. Foliar Fertilization of Crop Plants. Journal of Plant Nutrition, 32(6):1044-1064.
Fernandez, V., T. Sotiropoulos and P. Brown. 2013. Foliar Fertilization. In Scientific Principles and Field Practices. First edition. Paris: IFA.
Lang, G. 2005. Underlying principles of high density sweet cherry production. Acta Hort. 667:325-333.
Marschner H. 2002. Mineral Nutrition of Higher Plants. 3rd edition. London: Academic Press.
Neilsen, G. H., Neilsen, D., Hogue, E. J. and Herbert, L. C. 2004. Zinc and boron nutrition management in fertigated high density apple orchards. Can. J. Plant Sci. 84:823–828.
Nielsen D, P. Millard, G.H. Nielsen and E.J. Hogue. 1996. Sources of N for leaf growth in a high-density apple (Malus domestica) orchard irrigated with ammonium nitrate solution. Tree Physiology 17:733-739.
Neilsen, G.H. and D. Neilsen. 1994. Tree Fruit zinc nutrition, p. 85–93. In A.B. Peterson and R.G. Stevens (eds.). Tree Fruit Nutrition. Yakima: Good Fruit Grower.
Ouzounis, T and G. Lang. 2005. Foliar Applications of Urea Affect Nitrogen Reserves and Cold Acclimation of Sweet Cherries (Prunus Avium L.) on Dwarfing Rootstocks. HortScience 46(7):1015–1021.
Peryea, F.J., D. Nielsen and G. Nielsen. 2003. Boron maintenance sprays for apple: Early-season applications and tank mixing with calcium Chloride. HortScience 38(4):542-546.
Qazi, N. A, M.A Beig and K. Ahmad. 2005. Impact of post-harvest urea application on primary inoculum and infection of Venturia inaequalis (Cke.) Wint. and plant behaviour of apple. Applied Biological Research 7(1/2):37-43.
Righetti, T., K. Wilder, R. Stebbins, D. Burkhart, and J. Hart. 1998. Apples: Nutrient Management Guide. Oregon State University Extension.
Sanchez, E.E and T. L. Riguetti. 2005. Effect of postharvest soil and foliar application of boron fertilizer on the partitioning of boron in apple trees. Hortscience 40(7):2115-2117.
Weinbaum, S.A., I. Klein, F.E. Broadbent, W.C. Micke and T.T. Muraoka. 1984. Effects of time of nitrogen application and soil texture on the availability of isotopically labeled fertilizer nitrogen to reproductive and vegetative growth of mature almond trees. J. Am. Soc. Hortic. Sci. 109:339–343.
Wojcik, P. and M. Wojcik. 2006. Effect of boron fertilization on sweet cherry tree yield and fruit quality. J. Plant Nutri. 29:1755–1766.