Rapid Sap Nutrient Analysis Methods in Malus Domestica Borkh Cv. ‘Gala’

ABSTRACT

Sap quick tests are well established in vegetable crops. However, there is less equivalent investigation for perennial crops, such as apple trees. Accessing the nutrient content, as opposed to the foliar analysis, would increase the opportunity of adjusting the fertilization, along the growing cycle. This work evaluates the relation between the NO₃^−, K⁺, Ca²⁺, Mg²⁺, PO₄^3- and NH₄⁺ contents in apple petiole sap, measured with the RQflex^® test strips and laboratory methods to assess the possibility of using this tool with accuracy in in-situ sap analysis. Petiole samples were collected from six apple tree orchards, frozen and pressed. Dilution was mandatory for all nutrient determination, except NO₃⁻. The dilution factor varied with the stage of the annual cycle. The levels of NO₃⁻, K⁺, Mg²⁺, and Ca²⁺ followed the same pattern during the growing cycle, with both methods. Regression analysis resulted in high determination coefficients for NO₃⁻ (R² = 0.85), K⁺ (R² = 0.86), Mg²⁺ (R² = 0.81) and Ca²⁺ (R² = 0.95), between RQflex^® and laboratory methods. No equivalent relation was found for ammonium and phosphate determination. These tests can be useful tools for rational fertilization management, mainly in high-density apple orchards. The calcium content in 45 DAFB leaves correlated well with the calcium content in sap at the same timing.

KEYWORDS:

• Calcium
• magnesium
• nitrate
• potassium
• diagnostic methods

Acknowledgments

The authors would like to acknowledge the technicians of Campotec, Frubaça, Granfer, and INIAV for collecting leaf samples, according to the established protocol. This work was financed by LEAF UID/AGR/04129/LEAF and by PDR2020 under project MACFERTIQUAL PDR2020-101-031590.

Additional information

Funding

This work was supported by the MACFERTIQUAL [PDR2020-101-031590]; LEAF-Fundação para a Ciência e Tecnologia [UID/AGR/04129/LEAF] .