A hand-held refractometer is a relatively inexpensive optical instrument that measures the particulate level in an aqueous solution compared to mass. What that means in everyday language is that the tool gives an indication of the amount of sugar (and a few other things) in plant juice.
We can use these small devices to tell us the Brix value or the sugar content in the juice we extract from plant material. Along with other indications of plant health, we can use Brix values to help us make management decisions about our soils and crops. Brix is a unit of measure (technically degrees Brix) indicating the sucrose content of an aqueous solution. The scale in many basic hand-held refractometers ranges from 0-32. This scale is seen when looking through the viewpiece. If it is properly calibrated, the instrument should be set to zero when pure distilled water is placed on the prism of the refractometer.
Gathered plant material is put into a garlic press and squeezed to produce a drop or two of juice to place on the prism. Then, the user holds the refractometer up to a light source as if looking through a telescope and obtains a reading. This reading is useful if you know what a previous baseline reading was for that paddock or plant and you have a good idea what Brix reading those plants should have.
It can also be a great tool for people with dairy or nursing animals. Ruminants produce more quality milk when the sugar content in their forage is high. Therefore, knowledge of the sugar content of that forage in any given paddock is important. There are some target Brix values for various forage plants. For example, a Brix reading of eight seems to be average for alfalfa for many traditionally managed pastures. But, those raising cattle should be working to grow alfalfa with a Brix reading of above 16. For grain crops, a Brix reading of 14 is good with 18 being excellent. But for a crop that has naturally higher levels of sugar, say sorghum, the base levels are higher. In sorghum, I would think a farmer is seeking middle to high 20s Brix readings.
You don’t have to be a cattle rancher to make use of a refractometer. The savvy gardener knows that if the leaf of a plant that measures 12 degrees Brix or higher it will usually not be molested by insect pests. Agriculture and food industry expert Dr. Allen Williams confirms this notion. “High Brix forages are more resistant to disease, pests, and drought.” He also reports that good livestock performance correlates to high Brix levels. “We have seen higher animal performance when Brix levels in forages are higher,” he said referring to a 200-acre study in Independence, Kansas, USA.
Glen Rabenberg, soil expert and president of Soil Works LLC, said “A a sugar content of 13 percent or more is very beneficial for your plant’s insect resistance. We also know that if sugar content is low, plants will never grow to the extent of their genetic potential. These plants will also be low in minerals, vitamins, amino acids, and have poor general nutrition. These same low sugar plants have also lost some of the ability to draw moisture from the air, which now increases the effects of a drought.”
Wineries use refractometers to track when they should pick their grapes for the precise sugar levels they are looking for to make a specific kind of wine. Though most of us are not making wine, the sugar levels of our crops are important for us to know what’s going on in the soils as indicated by the Brix value of the plants.
One practical application of the refractometer is using it to help know the general ripeness of a fruit or vegetable. Testing a sample can give some indication to know what the optimal harvest time should be. For example, most industrial-scale cantaloupe growers will pick their melons when Brix values reach nine degrees. However, an excellent cantaloupe has a Brix value of 15 or higher. This can be the difference between that amazingly sweet cantaloupe you tasted from your grandparent’s garden compared to that crappy melon on most restaurant salad bars.
Rabenberg teaches that increasing Brix levels help an operation become more productive. Harmful fungi thrive in an area where plants measure a Brix value below seven. When ensuring there is the proper balance of available minerals and nutrients, the Brix levels are often in the 10-11 range. At this value, Rabenberg reports seeing drought resistance in the crops and fewer weeds nearby. Finally, when plants are measured at Brix values of 13 or higher, Rabenberg reports resistance to harmful insects.
Conducting Brix valuations needs to be done with some care. The samples must be gathered at the same time of day and in the same general weather conditions. Plants are moving sugars and other nutrients up and down their systems at different times of the day and different time of the year. We can obtain false comparisons if we conduct Brix testing in the morning and then a few days later in the afternoon when it’s warmer. We should also take samples from the same kinds of locations on the plant.
Plant samples must also be taken when there is similar sunlight. I recommend testing after the same amount of sunlight has been available and around the same temperature. Because the refractometer is impacted by temperature, it’s a good idea to ensure the device and the sample are about the same temperature. I like to let the sample juice rest on the prism glass for at least 30 seconds before taking a reading.
Growers should not view the refractometer as a magic wand. A refractometer gives you only one primary measurement. As useful as knowing what Brix values are in your plants, we can gain a lot more if we take this one data set and use it with other information to make decisions on our homesteads, farms and ranches.
What does it all mean for you? Plant health and related sugar levels are often dependent on the quality of life in the soil and how the soil’s microbiology is working in harmony with the root system of the plant.
Often, an unfavorable Brix reading can be an indication of low nutrient uptake in the plant due to poor microbial interaction in the soil. A first remedy I’d tell people to do before expensive soil testing and inputs is to make sure they are feeding the soil microbes well. Adding finished compost or compost tea or even raw milk are excellent way to feed the soil and thus ensure a healthy system below the surface.
[caption id="attachment_5001" align="alignnone" width="772"]
Brix value chart for typical fruits and vegetables.[/caption]]]>
