Figure 1. Lauren using the refractometer.
One assessment tool I started using during this study, which I find fascinating and surprisingly versatile, is the Brix meter, also known as a refractometer (Figure 2). It measures the light refracting through sap squeezed from a plant or fruit. The result is a percentage of dissolved plant solids by weight in a liquid which can be correlated with the plant’s food-producing efficiency (photosynthesis) and ultimate food quality. Graeme Sait, author of the book 'Nutrition Rules!' and the popular podcast ‘Nutrition Farming’, claims Brix readings can be used as an indicator of your effectiveness as a chlorophyll manager. That’s a leap in concept and well worth investigating.
Figure 2. A refractometer aka Brix meter.
With Brix, the sap’s dissolved solids include sugars, proteins, free amino acids, lipids, pectin and minerals which accounts for the higher percentage when compared with ‘Total Sugars’ from a laboratory leaf sap test which only measures sugars.
For example, when we test fruit juice, and the refractometer measures 15, the juice is 15% fermentable sugar even though all the dissolved solids in the juice are also affecting the Brix measurement.
Using Brix as a management tool requires an understanding of the variables that affect the consistency of readings. The time of day, maturity stage of the plant, microbial activity, mineral cycling in the soil and photosynthetic activity (sunny or cloudy) all influence the results.
If you want more information on the challenges of working with Brix, here’s a link to an excellent article by John Kempf, an expert in the field of biological and regenerative farming: The Challenges of Managing Nutrition With Brix Readings
There are many resources online listing desirable Brix levels for specific plants. Here’s a basic guideline from CompoExpert for understanding what the readings mean:
0 – 2 Brix: Very low Brix; the plant is essentially unable to ‘look after itself’. Insects will move in quickly to consume these plants and disease will run rampant.
3 – 7 Brix: Mid-level Brix; the plant has a chance of survival.
8 – 11 Brix: Higher Brix; natural resistance begins. Most sucking insects will not tolerate a Brix of 8 or higher; chewing insects that eat the roots or leaves directly will start to lose interest once the plant reaches a Brix level of 10 or 11.
12 – 20+ Brix: High Brix; virtually no insects will attack a plant with a Brix level of 12+.
Reading citrus and avocado leaves: Every two weeks we record Brix levels for, on average, six varieties of citrus and avocado leaves. We follow the NovaCropControl lab protocol of sampling both old and new leaves and the results are recorded. To compare temporal similarities, we plot Brix results with other minerals and sugars.
The optimal range of Brix (as per Ag-USA.net) for avocados is from 8-10, though consultants from South Africa aim for their trees to reach Brix levels of 16-22. The optimal range of Total Sugars (as per NovaCropControl data) for avocados is 2.2 to 3.7. These numbers are significantly lower than Brix because they only measure the sugar fraction. The relationship between Brix and Total Sugar results for young and old avocado leaves for a three-month period is presented in the following graph.
Brix is recorded every second week on-farm with the refractometer and Total Sugars every six weeks from samples sent to the lab.
Figure 3. Sample Relational Graph for Young and Old Avocado Leaves – Total Sugar and Brix
Reading our weeds: The refractometer can also offer a quick assessment of plant and soil health by comparing readings of weeds and adjacent crops on our farms. When the weed Brix is higher than the crop’s, you’ll know the soil is better suited for weeds, most likely due to compaction or a microbial imbalance. When the crop reads higher than weeds, the soil is at a more appropriate succession level for the crop. For more information: Brix Barometer
For more information on how to use a refractometer, check out Integrity Soils: The Use of Refractometers
And to learn more about interpreting results, check out Graeme Sait’s: The Beauty of Brix – Ten Things You Need to Know
This project is supported by the Canadian Agricultural Partnership, a federal-provincial-territorial initiative. The program is delivered by the Investment Agriculture Foundation of BC.
Opinions expressed in this document are those of the author and not necessarily those of the Governments of Canada and British Columbia or the Investment Agriculture Foundation of BC. The Governments of Canada and British Columbia, and the Investment Agriculture Foundation of BC, and their directors, agents, employees, or contractors will not be liable for any claims, damages, or losses of any kind whatsoever arising out of the use of, or reliance upon, this information.