Tree Fruit News: Nutrient Management in Apple Orchards for the 2023 Growing Season – CCE Eastern NY Commercial Horticulture Program

Lailiang Cheng and Mike Basedow, Cornell Cooperative Extension

Nutrient management plays a vital role in determining your orchard’s tree growth, yield, and fruit quality. Here are a few things to keep in mind when developing your orchard nutrition program this season.

Nitrogen:

The highest demand for nitrogen in the orchard occurs from petal fall to the end of shoot growth. During this period, rapid shoot growth and fruit cell division require substantial amounts of nitrogen. Nutrition studies have shown maintaining leaf N levels between 2.0 to 2.2% balances adequate tree growth with high fruit quality.

Fertigation is the preferred application method for N, as these applications can be made from bloom to the end of shoot growth to match peak N demand. If ground applications are made, the best timing is between budbreak and petal fall for most soils. The exception would be orchards on sandy soils with low organic matter. At these sites, multiple split applications from spring through early summer would be more desirable to limit nutrient loss.

The rate of N applied depends on the orchard soil organic matter content and tree N status. Because each orchard soil is unique, the best way to fine-tune your N rates would be to have your own N rate trial on your farm. Apply varying levels of N to a small subset of similar trees, and compare tree growth and fruit quality over multiple growing seasons. However, you might consider 20-50 lbs of actual ground applied N per acre where leaf analysis indicates a deficiency as a starting point. In Honeycrisp, if leaf N levels are above 2.2%, we recommend skipping N applications for a year.

Foliar N application at petal fall through the early cover sprays is a good way to supply nitrogen to young fruitlets and spur leaves. We recommend foliar urea applications at petal fall, first cover, and second cover at a rate of 5 lb. urea per 100 gallons on blocks that had marginal N status last year. Urea can be easily tank-mixed with most fungicides and insecticides, but cannot be mixed with oil. It should be applied as dilute sprays, but if you have to make concentrated sprays, do not concentrate urea over 3X.

Potassium:

Of the macronutrients required by apple trees, K has the highest concentration in fruit. More than two thirds of the total tree K requirement is found in the fruit. As a result, harvest removes a significant amount of K from the orchard. Work on Gala/M.26 has shown trees have constant demands for K from bloom to harvest. 80 to 85 lbs of K are removed at a fruit yield of 1500 bushels/acre in Gala, which equates to about 100 lbs of potash (K2O) per acre.

However, not all varieties are equal in their K needs. Honeycrisp requires lower K inputs compared to Gala and McIntosh; about 25-30% less K is needed when at similar levels of yield. With these findings in mind, we recommend the optimal leaf K levels in Honeycrisp as 1.0 to 1.3%, while the optimal for other varieties would be between 1.3-1.8%.

If your K level was marginal in last year’s leaf analysis, you should apply a higher than average amount of potassium this year in varieties such as Gala, McIntosh, and Empire.

If you use fertigation, target the period from petal fall to a couple weeks before harvest. Regular ground applications can be made at petal fall, after shoot growth has stopped, and following harvest. Typical ground application rates range from 60 to 150 lbs of K per acre at each application timing where leaf analysis indicates a deficiency. The lower end of this range should likely be used in Honeycrisp plantings, particularly if the block is prone to bitter pit. If your soil analyses show your Honeycrisp blocks contain 350 lbs or more of K in the top six inches of soil per acre, you should skip your K fertilizer for one to two years to bring the soil K levels back down.

Boron and Zinc:

Boron and zinc are both important for fruit growth and development. A foliar spray program of Solubor is a very effective management practice to supply B to fruit, while foliar applications of zinc are the only economical way of providing this element. We recommend applying Zinc chelate at the labeled rate, and Solubor at 1 lb per 100 gallons at petal fall and at first or second cover to promote early fruit growth. Zinc chelate and Solubor can be tank-mixed with urea. However, Solubor should not be tank-mixed with any pesticides contained in water-soluble plastic packages because it inhibits the dissolution of the plastic. Solubor should also not be tank-mixed with oil. Solubor increases spray water pH. Keeping this in mind, the pH of the tank mix should be tested and adjusted with a suitable acidifying agent if Solubor is to be applied with pH sensitive pesticides.

Calcium:

Ca accumulation occurs during the entire fruit growth period from petal fall to fruit harvest. In addition to having proper soil pH and maintaining calm trees, a foliar Ca spray program is essential for bitter pit susceptible cultivars. We have been recommending the following Ca spray program: 3 to 4 cover sprays of 1 to 2 lbs of calcium chloride (78% CaCl2) or its equivalent per 100 gallons (dilute basis) at 14-day intervals, beginning 7 to 10 days after petal fall, followed by 2 additional sprays of 3 to 4 lbs of calcium chloride (78% CaCl2) per 100 gallons at four and two weeks prior to harvest. It’s important to keep in mind that complete coverage of fruit is essential. More frequent sprays are more important than the exact timing of the sprays. Calcium chloride cannot be mixed with oil.

Maintaining proper soil pH

Soil pH should be maintained in the range of 6.0 to 6.5 throughout the soil profile to optimize tree growth and nutrient availability. New York orchard soils tend to acidify over time. The high annual precipitation gradually leaches calcium, magnesium, and potassium out of the soil. This loss of these elements leads to an increase in active hydrogen and aluminum, causing a decrease in soil pH. Ammonium-forming fertilizers (such as ammonium nitrate, ammonium sulfate and urea) also acidify the soil by releasing hydrogen ions as they convert to nitrate. To mitigate these acidifying effects, a soil analysis should be conducted every 2 to 3 years in mature plantings. If pH tests low, a maintenance lime application of 1 to 2 tons per acre should be applied.

For Honeycrisp, target your soil pH between 6.5 and 7.1 to ensure adequate calcium supply to minimize the risk of bitter pit.

Water/irrigation:

Dry fertilizers applied to soil cannot be taken up by the roots unless there is good soil moisture. Soil water status also affects the mineralization of organic matter, which consequently affects the amount of nitrogen available for the trees. Soil water availability also affects fruit cell division and cell enlargement, thereby affecting final fruit size. Providing irrigation to ensure water supply and nutrient uptake is essential for sizing the fruit to achieve high yield and good quality, especially if it turns out to be a dry year.