In perennial fruit trees, most nutrient uptake occurs between bloom and rapid vegetative growth. Sweet cherry root growth starts when soil temperatures reach approximately 59 F during spring, usually after bloom in Washington soils. According to Artacho and Bonomelli (2016), root growth of Gisela 6 rootstock started approximately 30 days after full bloom (DAFB), while the highest rate of fruit growth, associated to cell division stage, occurred between 21 and 28 DAFB. This result confirms that initial growth: bloom, pollen tube growth, spur leaf area, early shoot growth and early fruit development rely on reserves stored in roots, buds, and wood. Thus, fertilization of mobile nutrients should be programed accordingly to reduce losses. Here are some recommendations for sweet cherries grown in Eastern Washington.
The main questions we should consider before developing a nutrient management program are: What we need, and when do we need them? To answer the first question, one simple approach is to determine how much your crop and trees demands based on the predicted yield and adjusting the amount according to your system: soil, amendments and water is providing. The second question about when, related largely to the nutrient cycling in the soil and plant. For mobile ones, like Nitrogen (N), timing of uptake is an important consideration, while for non mobile ones, like P, timing becomes irrelevant.
Nitrogen (N): Mobile in the soil and in the plant. The demand in sweet cherries is generally higher than the soil plus water supply, especially in highly productive orchards. N demand in sweet cherry ranges between 2.7 to 14.4 lbs of N per ton of fruit (Geisseler, 2016, adapted from Fallahi et al. 1993, Silva and Rodriguez, 1995). In 2022, Sallato and Whiting (not publish), updated nutrient extraction values for WA cherries ‘Chelan’, ‘Skeena’ and ‘Coral Champagne (Table 1).
Diagnosing: Deficiency is reflected in a lack growth and general chlorosis (yellowing leaves) and smaller size fruit (Figure 1). Toxicity or excess will lead to excessive vegetative growth, delay harvest and reduced fruit quality. Symptoms will start in older leaves. Leaf tissue analyses of total N is a good indicator of N deficiency or excess. Note that N concentration in leaves start very high (around 3%) and will continues to drop to levels below 1.0% in the fall. Thus, when utilizing leaf tissue analyses as indicator, it is important to collect recently mature leaves, from current season shoots without fruits. Soil test of N is (NO3 or NH4) is not a good predictor of N supply.
Management: Trees take up N in the form of nitrate (NO3) and ammonium (NH4). One approach is to calculate N demand based on the expected yield (Table 1). Consider all possible inputs already in the system. The soil’s most important supply comes from the organic matter (O.M), generally low in Eastern Washington soils. A safe estimate should consider 10 pounds of N for every percent of O.M. in the soil. In some areas, irrigation water can provide large amount of N in the form of NO3 (readily available for plants), which can be determined with a laboratory test. Thus, the overall demand minus the combined supply will give you an estimate of the dose needed. Remember that N is very mobile and there are many important losses that will affect the efficiency of your application.
Table. 1. Nutrient extraction of in pounds (lbs) of nutrient per ton of fruit produced (US tons).
|Nutrient||lbs / US ton|
|Nitrogen (N)||4.3 – 4.8|
|Phosphorous (P)||0.71 – 0.86|
|Potassium (K)||4.2 – 6.0|
|Calcium (Ca)||0.3 – 0.4|
|Magnesium (Mg)||0.2 – 0.4|
- For inorganic products that are more readily available (urea, calcium nitrate, monoammonium phosphate, etc.) spread the application starting at petal fall up to a month prior to harvest.
- Excessive N applied close to harvest can reduce coloring and delay harvest.
- If trees are too vigorous, or there is a low crop (due to frost or pollination problems), the demand should be adjusted.
- Fertigation can help to reduce losses due to volatilization and better distribution to the target crop, especially in sandy soils.
- If applied dry to the ground, irrigate right after the application to allow solubilization and movement into the soil profile.
- In the fall, foliar application of N will help to build reserves for the next season. Soil application of N during the fall is not recommended.
Phosphorus (P): very immobile in soil, very mobile in the plant. Plants absorb P as H2PO4– by an active (energy-requiring) process. Demand by sweet cherry orchards is low compared to N and K. According to Silva and Rodriguez (1995), sweet cherry demand approximately 1.5 pounds of P for every ton of fruit. Many soils in Eastern Washington have low levels of available P, especially in silty soils at deeper soil levels, which might explain why extraction levels in WA cultivars range between 0.71 and 0.86 Lb per ton of fruit (Table 1).
Diagnosing: Deficiency can lead to reduced growth and stunting and red dark coloration of leaves because of enhanced anthocyanin pigments. P is very mobile in the plant therefore deficiencies will show up first in older leaves (Figure 2)
Management: Soil test of P-Olsen is a good indicator of P availability. In the soil, levels should be maintained between 15 – 40 mg/kg. If P-Olsen levels are below 15 mg/kg, a single application of 40 pounds of P2O5 per acre will provide enough P for a couple of seasons. If levels are very low (below 5 mg/kg) correcting P levels in the soil will take several years. Because of the low mobility in soils, P can be applied at any time, and all at once, with no risk of losses. This lack of mobility, though, makes it harder to move in depth, and can lead to deficiencies when the fertilizer doesn’t reach the root zone. Thus, best time to fertilize with P is during soil preparation before planting.
- P availability is reduced in soil pH below 6.5 and above 7.5. Managing the pH will benefit overall nutrient availability.
- If soil P is high or adequate and nutrient levels in the plant are low, the problem is likely related to uptake limitations for example nematodes, pathogens, excess or lack of water, poor root health, among others.
Potassium (K): Mobility of K in the soil depends on soil texture and cation exchange capacity (CEC). In sandy coarse soils, K can be very mobile and leach out of the root zone, especially in heavily irrigated conditions. In heavier soils (loamy, silt loam or clay), K has low mobility and can accumulate over the years. In the plant, K is very mobile, and the demand has been estimated in 4.2 to 6.0 pounds per ton of cherries (Table 1).
Diagnosing: Deficiency will first develop in older leaves as yellowing or necrosis of leaf margins (Figures 2 and 3). Reduced K has also been associated to reduced fruit size and soluble solid content. Toxicity has not been reported, however, excessive levels of K in the soil is antagonistic to Ca and Mg uptake, leading to nutrient imbalance and reduce fruit quality.
Management: Deficiency of K in Eastern Washington is infrequent, while excessive levels have been reported in several growing areas (Sallato, unpublished). Maintain soil levels between 150 to 300 mg/kg (Exchangeable P). If levels are above 300 mg/kg, there is no need for K application in sweet cherry. If levels are below 150 mg/kg, correct by adding 120 pounds of K2O per acre. Verify the nutrient levels the following year to adjust the dose is needed. Timing is not relevant in loamy or heavier soils (similar to P), however, in sandy soils, is better to spread the application during spring (similar to N).
- Excessive levels have been observed in soils of all textures in Eastern WA cherry production, including sandy soils if there are variable textures thought the profile (soil layers) that prevent leaching.
- High levels of K have been observed in soils previously cropped with potatoes or dairy farms.
- Manure and compost can contain high levels of K. Verify the composition with a laboratory test or requesting a laboratory test to the provider.
- If soil K is high or adequate, and nutrient levels in the plant are low, there might be other conditions limiting uptake: nematodes, pathogens, excess or lack of water, poor root health.
- If root uptake of K is limited, foliage sprays can be temporarily justified, but would not solve the problem.
Calcium (Ca): Mobility in the soil depends on texture and cation exchange capacity (CEC). In sandy coarse soils, Ca can be mobile and leach out of the root zone, especially in heavily irrigated conditions. In heavier soils (loamy, silt loam or clay type of soils), Ca has lower mobility and can be retained by the negative charges of the soil and O.M. Many Eastern WA soils have large amounts of Ca (above 10 meq/100g), usually associated to high pH and presence of caliche or lime (CaCO3). While Ca availability is reduced in high pH soils (above 9.5) or acid soils (below 5.5), the available portion in the root zone is in constant equilibrium with the not available portion. In cases with high Ca levels (above 8 meq/100g), adding more Ca would not improve uptake. Irrigation water can also contain high levels of Ca and CaCO3 that will contribute to the amount of Ca available for plant uptake. In Eastern WA deficiencies have only been reported in very sandy soils (Quincy, Mattawa and Sagemoore soil series). Regarding plant demand, Ca demand is estimated between 0.3 and 0.4 pounds per ton of fruit in sweet cherry.
Diagnosing: Calcium is part of the cell wall and key to cell wall strength. Calcium deficiency has been associated to fruit cracking and firmness in sweet cherry (Demarty et al., 1984, Christensen, 1996). Fruit with higher levels of Ca have reduced cuticle permeability (Christensen, 1996) and greater cell wall strength (Glenn and Poovaiah, 1989). While Ca has been largely associated to fruit firmness, the relation with fruit quality and storability is contradictory and yet to be determined in WA-grown varieties.
Management: Leaf tissue test is a good tool to determine uptake, however, does not correlate as well with fruit Ca uptake. Several factors, other than Ca supply, can prevent Ca movement into the fruit, for example, excessive N and vegetative growth, shade, stress, etc. If Ca levels in the leaf are deficient, fruit Ca will likely be deficient, but adequate Ca levels in the leaves, do not always imply adequate levels in the fruit.
Standard soil test of exchangeable Ca is a useful tool to determine soil Ca availability. If soil levels are below 4 meq/100g or 800 mg/kg, correct via soil application during the spring. There are many commercial products that will provide different forms of Ca. Gypsum (CaSO4), is an economic source of Ca that will also provide sulfate. If N levels are also low, CaNO3 is also a good alternative. If salt levels in the soil are not a problem, CaCl2 is an economic alternative for conventional growers.
Foliar application are not as effective as soil applications. The following are some exceptions that justify foliar applications:
- Excessive potassium levels (K) in the soil (above 300 mg/Kg or ppm).
- Cold and dry soils (below 59 F) after full bloom.
- Limitations in the root zone: pathogens, physical limitations, excessive or lack of water, nematodes, etc.
Applications of Ca during the pre-harvest window have been reported widely in sweet cherry in attempts to reduce rain cracking, however, results are contradicting. Post-harvest dipping in CaCl2 solutions have been widely recognized in reducing cracking and to prolong stem greenness (Wang and Long, 2015). Wang and Long (2015), recommended a solution with 0.2 – 0.5% CaCl2 (equivalent to 2000 – 5000 ppm CaCl2) for five minutes, then passing the fruit through cold flume water (0 C) for 15 minutes to increase firmness and skin brightness and to reduce splitting incidence and pedicel browning.
- Ca uptake in sweet cherry is maximum during spring, starting around 25 days after full bloom, with new root growth.
- If soil pH is above 8.5 or CaCO3 is high, is better to manage the pH rather than trying to add more Ca to the soil.
- In sodic soils (high levels of sodium Na), CaSO4 (Gypsum) application can help remove the excess of Na and improve soil structure. Make sure you have good drainage.
- CaCl2 is not recommended for soils with high levels of salinity or bad drainage (impermeable layers). Can not be apply through the soil in organic production.
Magnesium (Mg). Mobility in the soil depends on texture and cation exchange capacity (CEC). In sandy coarse soils, Mg can be mobile and leach out of the root zone, especially in heavily irrigated conditions. In heavier soils (loamy, silt loam or clays), Mg can be adsorbed by the soil particles. Like Ca, deficiency is Eastern WA is infrequent, but can be found in sandy soils with excessive drainage. Mg has moderate mobility in the plant. Regarding plant demand, is estimated between 0.2 and 0.4 pounds per ton of fruit (Table 1).
Diagnosing: Visual symptoms of deficiency appear in older leaves first as interveinal chlorosis that can lead to interveinal necrosis (Figure 3). Leaf tissue analysis are good indicators for Mg uptake by the plant and fruit.
Management. When deficient, correct soil levels with the application of 30 pounds of MgSO4 (Epson salts). Foliar applications of MgSO4 are also effective in reducing deficiencies when root uptake might be limited or in soils with excessive K. As most nutrients, maximum uptake occurs during the spring with rapid growth.
- Excessive potassium levels (K) in the soil (above 300 mg/Kg or ppm) can prevent Mg uptake.
- Excessive application of lime CaCO3 or CaSO4 can prevent Mg uptake.
Sulfur (S). Mobile in the soil and mobile in the plant. Deficiency has been detected in many Eastern Washington soils, but deficiency can be easily corrected.
Diagnosing: Deficiency symptoms in leaves are very similar to N deficiency, with generalized yellowing of leaves and smaller size leaves. Leaf tissue analyses can help diagnose a deficiency.
Management: If nutrient levels are low, utilizing sulfate-based fertilizer, such as CaSO4, MgSO4, ZnSO4, etc. will improve soil SO4 levels. Application of Gypsum will also improve both, S and Ca deficiencies when present.
- Burning of leaves can occur with leaf applications if air temperatures is greater than 85 ºF.
Boron (B): Mobile in the soil and very low mobility in the plant. In a recent prospection of more than 170 Eastern WA soils, all samples were B deficient (below 0.5 mg/kg) (Sallato, unpublished). Its availability can be limited with soil pH between 7.0 and 8.5, which is very common in Eastern WA. Other factors such as cold soils during spring or dry conditions can limit B uptake.
Diagnosing: B is fundamental for meristematic growth in roots and shoots. Thus, a very distinctive symptom is the death of new shoot tips. It is also important for pollen tube growth during the pollination process, and deficiencies can also affect fruit set and yield. Leaf B analyses are a good indicator of overall uptake but do not correlate well with fruit B levels.
Management: Maintain adequate levels of B in the soil (between 0.5 and 1.5 mg/kg). In deficient blocks, spring or late dormant application to the trees are highly recommended for better fruit set. The application rate should be carefully calculated, as toxicity can easily be reached even with small doses. Foliar spray rate should not surpass 0.5 pounds of actual B per acre.
Iron (Fe), Manganese (Mn), Cupper (Cu) and Zinc (Zn): Demand for these nutrients is small, however essential for growth, development, and fruit quality. Most deficiencies in WA soils are associated to their reduced availability in high pH soils, or anoxia in the root zone (excess of water and lack of oxygen). Under these conditions, soluble forms of these elements are precipitated and not available for plant uptake.
Diagnosing: Visual symptoms of Zn and Fe deficiencies are distinctive. Zn deficiency develops blind wood, little leaves in a rosette, with short internodes. Fe deficiencies are also very distinctive with yellowing in the entire blade (Figure 4). In high pH soils Fe availability is most affected and will develop symptoms that can mask other deficiencies. Deficiencies start in young leaves. Mn and Cu deficiencies are less distinctive and normally hidden. The best diagnostic tool for these elements is soil pH or alkalinity (effervescence), and visual symptoms.
Management: When deficiencies of metallic micronutrients are due to high soil pH, correcting nutrient levels through the soil is inefficient, although good results have been obtained with chelated forms applied through the growing season. The recommended practice is to manage soil pH, which will improve micronutrient availability. Foliar sprays of Zn during spring or delayed dormant have also shown to be effective in reducing deficiencies. If deficiencies appear during the season, frequent applications are more effective, given the poor mobility in the plant.
To monitor if we are in the right path, leaf tissue analyses are very useful to determine uptake, and if trees are in a deficient or excessive condition.
Visual symptoms can be a useful tool to diagnose nutrient deficiency or excess, but it is important to keep in mind that symptoms can be confused with other problems. For example, insects, diseases, pesticide toxicity, or abiotic stress associated to excess or lack of water, wind or heat (Figure 5). An appropriate diagnostic process should consider alternative tools (soil, tissue test).
Nutrient management in sweet cherry is based on leaf tissue standards, useful in preventing deficiencies or toxicities. These standards were developed by determining nutrient concentration at maximum growth and have not taken fruit quality nor storability into account (i.e., there are no nutritional standards related to optimizing fruit quality). This year, WSU research and extension faculty Sallato, Whiting and Torres initiated a three-year project titled “Nutrient Management for High quality Sweet Cherries” funded by the Washington Tree Fruit Research Commission (WTFRC) and the Oregon Sweet Cherry Commission (OSCC). The goal of this project is to improve nutrient management strategies for better fruit quality and storability. The expected outcomes of the project will provide a better understanding on the relation between fruit quality and nutrient composition, as well as variety specific values of nutrient extraction for our local growing conditions.
Tree Fruit Extension Specialist
Washington State University