Tissue Analysis Interpretation in a Bearing Apple Orchard
A New York apple grower has a bearing block of Honeycrisp on M.9 rootstock. Leaf samples were collected at 60-90 days after bloom from mid-shoot leaves. Results: N 1.9%, P 0.12%, K 1.1%, Ca 0.7%, Mg 0.35%, B 18 ppm, Zn 12 ppm. Reference sufficiency ranges for bearing apple: N 2.0-2.6%, P 0.15-0.30%, K 1.2-1.8%, Ca 0.8-1.2%, Mg 0.30-0.50%, B 25-50 ppm, Zn 15-30 ppm. The grower wants to apply a foliar micronutrient mix and additional N. The orchard has a history of bitter pit.
1. Interpret the leaf analysis relative to sufficiency ranges and prioritize which nutrients to address.
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Compare each value to the sufficiency range:
- N 1.9% - below range (2.0-2.6)
- P 0.12% - below range (0.15-0.30)
- K 1.1% - below range (1.2-1.8)
- Ca 0.7% - below range (0.8-1.2)
- Mg 0.35% - within range
- B 18 ppm - below range (25-50)
- Zn 12 ppm - below range (15-30)
Priorities: Ca is low and the orchard has bitter pit history, so Ca is the top priority. B is low and affects fruit set and Ca transport. N is slightly low but excess N can worsen bitter pit by promoting vegetative growth and diluting Ca. P and K are low but K excess can antagonize Ca and Mg. Mg is adequate. A balanced approach: address Ca and B first, correct N modestly, and avoid over-applying K. Zn can be corrected with a foliar spray.
2. Explain the interaction between N, K, and Ca in the context of bitter pit and recommend a foliar program.
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Bitter pit is a Ca deficiency disorder in fruit, often occurring even when leaf Ca is adequate because Ca moves with the transpiration stream and is poorly redistributed to fruit. High N promotes shoot growth and competes for Ca; high K and Mg antagonize Ca uptake. Therefore, applying more N and K without addressing Ca can worsen bitter pit.
Recommendation:
- Apply foliar Ca (e.g., calcium chloride or calcium nitrate) at 3-6 lb/100 gal several times during the season, starting at petal fall and repeating every 2-3 weeks.
- Correct B with a foliar spray (e.g., Solubor at 1-2 lb/ac) to support Ca transport and fruit set.
- Apply moderate N only if needed (e.g., 20-30 lb N/ac) and avoid excessive K.
- Maintain soil Ca and pH; consider gypsum if soil Ca is low.
- Monitor fruit Ca and bitter pit incidence.