Orchard Nutrition

Orchard nutrition is vital to the health of trees and long term yields in orchards. In Montana, soils are often low in organic matter and available nutrients due to our cold, arid climate—which limits decompostion—and young soils—which can be coarse and sandy. This results in soils that are often low in natural nutrient availability and holding capacity. These inherent attributes should be considered when evaluating the nutrition of tree fruits and developing orchard nutrition management plans. Before applying fertilizer, consider potential barriers to uptake due to poor soil conditions including high or low soil moisture, compaction, or restrictive soil layers. Each of these soil conditions can lead to poor root growth, as well as reduced oxygen and moisture, which are important for nutrient cycling and uptake. These factors should be addressed alongside foliar and soil amendments to achieve balanced orchard fertility.

Monitoring Orchard Nutrition

Good nutrition management starts with knowing your soil and your trees through regular testing, monitoring of yields, vegetative growth, and visual symptoms of deficiencies or toxicities. Good record-keeping is essential for responding appropriately to orchard nutrition issues from year-to-year, starting with a soil test at establishment.

Before planting, soil should be tested for pH, organic matter, salts and primary nutrients (N, P, K, S, Ca, Cu, B, Zn, Fe, Mg and Mn). Additionally, soil texture and physical characteristics should be evaluated to address issues including restrictive layers such as hardpans or clay lenses, compaction or high clay content that might lead to poor drainage and root development. While soils are highly variable from orchard to orchard and even within a particular site, in general, Montana soils tend to have high soil pH, low organic matter, limited micronutrients, and are calcareous (high in calcium). Soil texture varies greatly, from extremely coarse (sandy or even gravelly) or high in clay. These characteristics can contribute to limited nutrient availability, poor nutrient cycling, and low water holding capacity, resulting in poor root growth and nutrient uptake.

Soil test results prior to orchard establishment should inform soil amendments at planting, in particular with nutrients that are less mobile in the soil, like phosphorus, potassium, and organic matter. Once established, regular soil testing should be done every 2-3 years to monitor for deficiencies or toxicities. However, soil testing is limited after establishment and should be paired with annual foliar testing to determine actual tree uptake of important nutrients.

Timing of foliar sampling is crucial to providing informative results. Foliar testing should be done in late July/early August after terminal buds have set and before trees begin reallocating nutrients in preparation for dormancy. Timing should be consistent to provide comparable results with standards in the lab but also across years in the orchard. Each laboratory has specific instructions for collecting samples, but multiple samples should be collected if differences in yield, growth or tree health are observed in different areas of the orchard to help determine if nutrition is a factor.

Based on test results, labs will provide growers with recommendations for addressing orchard nutrition. These are based on standards developed using averages of nutrients found in common cultivars for specific species (see Table 1). Annual testing will demonstrate if products, rates and other management practices addressing nutrient uptake are helping. These results should also be used to prevent over-application of fertilizers, resulting in phytotoxicity, wasted money, and environmental degradation.

Nutrients

All trees require both macro- and micronutrients to perform vital functions and maintain fruit production. The primary difference between these categories of nutrients is not in the importance of the nutrient to the tree but in the amount it needs. Nutrition plays an important role in balancing vegetative growth and fruit production to achieve consistent yields and high quality fruit.

Nitrogen (N)

Nitrogen fuels vegetative growth and must be carefully monitored to maintain adequate levels. Too little N will result in poor vegetative growth and may be visually observed as yellowing of young leaves or poor shoot growth. Too much N results in excessive vegetative growth at the expense of fruit quality and yield, poorly-colored fruit, and fruit storage issues. It can also delay plant dormancy, resulting in higher susceptibility to winter injury. In addition, fire blight, a common disease in Montana apple and pear orchards, spreads faster in excessively vigorous trees.

Application of nitrogen fertilizer should be done in the spring and no later than mid-July. Nitrogen rates will depend on tree age, desired yield, soil texture and organic matter content, and leaf tissue analysis. General recommendations are 0.01-0.04lbs N per tree per year of age, not to exceed 0.3lbs N per year. In addition to tissue analysis, vegetative growth is also an indicator of adequate N (see Table 2). However, vegetative growth can also be limited by water, so growers should consider irrigation management when evaluating nitrogen status in terms of vegetative growth.

Phosphorus is important to energy cycling and root growth. Symptoms of deficiency usually include dark green to bluish leaves. In a survey of 23 Montana orchards, only three were found to have low P levels, but deficiency was not found in any of the foliar samples indicating uptake was still adequate in all Montana orchards. Phosphorus is not very mobile in the soil, however, so should be applied to the rootzone based on soil test results at planting. While reserve P can be applied for long-term release to plants, excess P can limit zinc and iron uptake and lead to water quality issues if eroded into water by runoff or excess irrigation.

Potassium (K)

Potassium is a critical nutrient in water uptake, food storage and the transfer of other nutrients, such as calcium. Deficiency is usually exhibited by yellowing or necrosis (browning and death) of leaf margins. It is not commonly deficient in Montana soils but was reported as low in 26% of foliar samples collected in 23 Montana orchards. Good root health and optimal irrigation (i.e., that keeps the soil consistently moist—neither dry nor saturated) are important for K uptake. Potassium uptake may be limited in dwarf rootstocks under drip irrigation even when soil levels are sufficient (Sallato, et al. 2019). Potassium is most often soil-applied. Foliar applications are only recommended when soil is depleted of K. Recommended rates for maintaining K nutrition depend on soil levels and yield but range from 0-150lbs/acre depending on soil tests.

Calcium (Ca)

Calcium is an important nutrient in cell wall development, and deficiencies can lead to bitter pit, cork spot, and other storage issues. Apples are not good at translocating Ca and often are deficient even when soil levels are high. For example, despite all Montana orchards surveyed having normal to high ranges of soil Ca, 73% of orchards had foliar samples that were deficient in Ca. Orchard management from pruning and crop load management to irrigation can help improve Ca uptake. These measures include controlling vigor by not over-pruning or -fertilizing with N, irrigating consistently, thinning fruit, and addressing fertility issues—including B deficiency and excess K and Mg. In scenarios where soil Ca is sufficient but foliar content is low, Ca sprays can be applied to increase uptake. Recommendations depend on foliar results but range form 3-12 sprays per season. Calcium chloride is the most effective form and can be applied at rates ranging from 2-4 lbs/acre for a total application of 15-50 lbs/acre of calcium chloride in a growing season. Sprays should begin after petal fall around mid-June and continue based on orchard needs through mid-August.

Boron (B)

Boron deficiency is common in Montana orchards as a result of low soil B. Deficiency symptoms include wilted blossoms, shoot dieback, poor pollination, dwarfed leavesm and deformed fruit. Boron deficiency can look similar to Zn deficiency. In a survey of 23 Montana orchards, 84% had low levels of soil B and 47% of foliar samples were deficient in this important nutrient.

Boron deficiency should be corrected through both foliar and soil applications paired with careful monitoring to avoid toxic levels. Soil applications of 2-5lbs/acre every 3 years alongside annual foliar application of 0.5-1lb/100 gal will improve B nutrition. Boron is very mobile in the soil and should be applied in the fall after harvest in heavy soils and in the spring on coarser soils.

Magnesium (Mg)

Interveinal chlorosis (yellow leaves with green veins) is a symptom of insufficient Mg. In general, Montana soils have adequate Mg; therefore, deficiencies may be related either to an imbalance in K and/or Ca or to saturated soils, which would inhibit B availability to the plant. If soil levels are adequate, but foliar samples report deficiencies, address irrigation issues and apply Epsom salts at a rate of 15lbs/100gallons after petal fall every 2-3 weeks for a total of three sprays. If soil is also deficient, fertilize per the recommended rate based on soil tests. Foliar sprays only provide a short-term solution.

Manganese (Mn)

Similar to Fe and Mg deficiency, Mn deficiency results in interveinal chlorosis on young leaves. In a survey of Montana orchards, no deficiencies were observed in foliar samples. Mn is most often deficient in sandy soils and is best applied as a foliar spray as soil-applied Mn is quickly bound in the soil. Toxicity issues can occur in saturated or acidic soils, which are rare conditions in Montana.

Iron (Fe)

Iron deficiency is common in high pH soils and soils with restrictive layers preventing water drainage and impeding root growth. Symptoms include interveinal chlorosis, where leaves can become pale green yellow to nearly white. Often iron deficiency is caused by high pH soils, irrigation water high in bicarbonates, saturated soils (particularly in spring), or other soil conditions limiting oxygen and water drainage.

Foliar tests are not the best indicators of Fe levels. If symptoms are present but Mn, Mg and Fe levels are reported adequate, iron uptake should be addressed through improving soil conditions, including letting soils dry between irrigation events, reducing soil compaction, and using acidifying fertilzers to improve pH in the root zone. Providing supplemental iron in the form of foliar-applied iron chelates may provide temporary relief but these are quickly oxidized and made unavailable to plants.

Zinc (Zn)

Like B, Zn deficiency is common in Montana due to our high pH soils. In a survey of Montana orchards, 65% of foliar samples had low levels of Zn. Zinc deficiency can look similar to B and induces whorls of small leaves and blindwood. Soil-applied Zn is ineffective, as it is quickly adsorbed in the soil, especially when P is elevated. Foliar applied Zn is recommended as a regular maintenance spray in orchards. Zinc sulfate, Zn oxysulfate, and Zn chelates all can improve Zn levels in tree fruits; however, growers should read product labels carefully to avoid damaging trees and equipment. The recommended maintenance rate of zinc sulfate is 2-4 lbs/acre applied at silver tip in pome fruits. Applications during the growing season may cause fruit russetting. Chelated forms should be applied at the labeled rate and have less risk of damaging fruit but can be more costly. Zinc oxide has been shown to be less effective and more damaging to trees and fruit.

Copper (Cu)

Copper deficiencies are rare in Montana, particularly in orchards using Cu sprays as pesticides. Deficiencies can be corrected with improved irrigation—especially in dry conditions—and by using dormant sprays. Excessive soil Cu can interfere with uptake of other nutrients including Zn, Fe, and Mn, so soil applications should be avoided.

Applying fertilizers and foliar sprays

Montana orchards generally require maintenance applications of B, Zn and Ca. Most orchards will also need annual application of N-P-K to keep up with crop demand based on yield. How much to apply will largely depend on foliar and soil test results and grower production goals. Labs can provide recommendations to guide application rates which can be used with regionally-available spray schedules to inform timing and available products.

Sample spray schedules

WSU Tree Fruit Crop Protection Guide Nutrient Spray Schedule

Intermountain West Tree Fruit Guide Nutrient Spray Table

For more information on calculating spray rates based on crop demand and predicted yield visit WSU Tree Fruit Soil Fertility and Plant Nutrition Cropping Orchards in Central Washington.

Disclaimer: These recommendations are provided only as a guide. It is always the pesticide applicator’s responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned. The authors and Montana State University assume no liability resulting from the use of these recommendations.

Resources

Peryea, Frank. 2018. Think Zinc! Visited 12/23/21. http://treefruit.wsu.edu/zinc/

Sallato, B., Dupont, T. Granastein, D. 2019. Tree Fruit Soil Fertility and Plant Nutrition in Cropping Orchards in Central Washington. Accessed online 12/23/21: http://treefruit.wsu.edu/orchard-management/soils-nutrition/fruit-tree-nutrition/

Spetrum Analytics. No date. Fertilizing Apples. Accessed online 12/23/21: https://www.spectrumanalytic.com/support/library/pdf/fertilizing_apple_trees.pdf

James, D.W. and Topper, K.F. 2010. Utah Fertilizer Guide. Accessed online 12/23/21: https://extension.usu.edu/agwastemanagement/ou-files/nmp_template/Utah_Fertilizer_Guide.pdf

Whitney, G. No date. Irrigation and Iron Chlrosis. Accessed online 12/23/21: https://extension.wsu.edu/chelan-douglas/agriculture/treefruit/irrigation/irrigationandironchloroisinorchards/

Intermountain Tree Fruit Production Guide. 2021. Accessed online 12/23/21: https://intermountainfruit.org/nutrition/nutrients.