To know whether sugarcane is mature, measure the Brix of juice from the top and bottom parts with a hand refractometer. In immature sugarcane, the top to bottom ratio stays below 1, and as the sugarcane matures it comes near 1. The firm decision is made from lab pol and purity.
The reason: sugarcane matures from the bottom up
The bottom part of sugarcane matures first and the top part last. So looking only at the Brix of bottom juice can make the field seem mature, while the top may still be immature. According to ICAR-Sugarcane Breeding Institute (SBI), Coimbatore, in immature sugarcane the top/bottom Brix ratio is below 1. As sugarcane matures, this ratio moves near 1.
How to do the test in the field
- Tools: A Hand refractometer and a punch to take out juice.
- Choose stalks: Take stalks from different parts of the field. Take at least 2 stalks from one clump. Do not take stalks only from the edge of the field.
- Take juice: From the top part and bottom part of each stalk, take juice with the punch and note the Brix.
- Calculate: Top Brix ÷ bottom Brix = ratio. An example to understand the calculation: if the top is 18 and the bottom is 20, the ratio is 0.9.
- Keep a record: Note the field, variety, planting date and Brix. If you measure again after a few days, you will see which way the ratio is moving.
Brix is an estimate, not the final answer
LSU AgCenter also treats Brix as only an approximate measure taken in the field. According to SBI, sugarcane is considered mature when juice pol is above 16 and purity is above 85%. These figures come from a small mill test and a lab, not from a refractometer.
Check early, 4 to 6 weeks before harvest
SBI guidance says to start checking at least 4 to 6 weeks before the expected harvest date. Keep plant and ratoon crops separate. Group fields by variety and month of planting. Then start harvest from the fields with higher Brix. According to SBI, this arrangement gives a more evenly mature crop, and an improvement of 0.2 to 0.5 percent in sugar recovery has been recorded. This figure was recorded at mill level; it is not a promise for every field.
What affects the time of maturity?
- Soil fertility and fertiliser
- Irrigation
- Pests and diseases
- Variety and weather
Immature sugarcane causes loss, and so does over-mature sugarcane. SBI advises avoiding both. So decide by measuring, not by looking at the calendar. According to LSU AgCenter, the lower internodes mature first, and as the season moves on, Brix must also be checked in the upper part of the stalk. Comparing the Brix of different fields shows which field to cut first.
Questions and answers
Does a Hand refractometer show pol?
No. A refractometer gives only Brix, which is an approximate measure. For pol and purity you need a lab or a small mill test.
If the ratio reaches 1, should I cut right away?
When the ratio comes near 1, it means the sugarcane is close to maturity. Make the final decision after looking at pol, purity and the mill's harvest date.
Sources: ICAR-Sugarcane Breeding Institute, Coimbatore: FAQ on cane quality · LSU AgCenter: Estimating Brix values to improve sugarcane quality
*Farmers' results are their own experience, not a guarantee. Results change with soil, water, weather and care.
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