Plant sap analysis: what plants tell us about nutrition
Sap analysis measures nutrients in liquid extracted from specified tissues. It can inform nutritional status at sampling and help follow changes through a season.
From soil to plant
Soil tests assess properties and nutrient availability; dry-tissue analysis measures concentrations in collected plant parts. Sap analysis examines liquid extract, with results depending on tissue and extraction method.
AEA’s approach
John Kempf’s Advancing Eco Agriculture uses repeated sap analyses with farmer observations and other agronomic data to identify possible shortages or excesses and monitor interventions.
Young and old leaves
AEA guidance collects younger and older leaves separately to examine nutrient movement. Young leaves must be sufficiently developed; older leaves should remain green and functional. Immature or senescent leaves can distort the picture.
Sampling determines value
Comparisons need consistent leaf age, growth-stage records, similar collection times and correct preservation. Follow laboratory instructions concerning recent foliar applications: residues, delays and poor storage can affect results.
Crop-appropriate interpretation
A 2026 controlled-environment study compared five sap extraction methods with established leaf analysis in tomato, cucumber and lettuce. Agreement varied by crop, nutrient and stage, demonstrating the need for suitable methods and reference values. Olive testing therefore requires an appropriate protocol and evidence-based interpretation.
Our field work
We aim to explore sap testing alongside leaf diagnostics and soil microscopy, connecting food web functions with olive nutrition and responses.