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lemons in the greenhouse

October 2021 - More about Leaf Sap Analysis

Robertson Navel Orange leaves ready to be squeezed for sap analysis.

Leaf sap analysis for plants is like a blood test for us.

It indicates the state of health at the time of sampling. Old and young leaves are sampled separately and the difference in levels for specific nutrients gives us clues as to how well the plant is functioning.

Attention is paid to which nutrients are in the sufficiency range, and which nutrients are either excessive or deficient. When interpreting results, it’s also important to understand anion and cation antagonists and to understand the mobility of different nutrients when comparing results of old leaves versus new leaves.

Test results can indicate a problem before the plant manifests it. And quick response using foliar applications of specific nutrients can help the plant overcome the imbalance.

Identifying the sufficiency range, or target values, for avocado and citrus sap is in progress.

As more growers use this system of analysis the ranges will be refined.

Getting leaf samples to the lab before they start to decompose! We live on a small island near Vancouver and no matter how much I pay for shipping; samples won’t reach the lab and be analyzed for at least a week and often up to 12 days after the samples were collected. Packaging with a cold pack in warm weather helps. The length of time from sampling to analysis should be considered when reviewing results. For example, I’ve noticed the longer the trip the higher the ammonium level.

Size matters, how big is that sample block? Leaf samples for the labs require 120 grams of both old and young leaves. This may not seem like a lot but with monthly sampling it wouldn’t take long to defoliate one of these semi-dwarf trees. I’ve since learned that growers often choose a block of 20 trees for each set of samples. I’ve had to adjust my study by reducing sampling to once every 6 weeks and to harvest leaves from multiple trees.

And we also do on-farm sap analysis. Every two weeks we sample at least 5 trees using Horiba LaquaTwin and Brix meters for on farm analysis. Our meters test for nitrate, potassium, sodium, pH, EC and calcium. The data from these tests will be compared with results from the labs in our final report.

The following links are to videos demonstrating the steps involved in on-farm sampling:

#1. Collecting Leaf Samples for Sap Analysis

#2. How to Squeeze Sap from Leathery Leaves

#3. Calibrating the LaquaTwin Meters

#4. On-Farm Analysis of Leaf Sap

And here's a link to a recently published research paper specific to citrus sap analysis by the University of Florida:

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