Harvesting of sugarcane at a proper time i.e., peak maturity, by adopting right technique is necessary to realize maximum weight of the millable canes (thus sugar) produced with least possible field losses under the given growing environment.
On the other hand harvesting either under-aged or over-aged cane with improper method of harvesting leads to loss in cane yield, sugar recovery, poor juice quality and problems in milling due to extraneous matter.
Therefore, proper harvesting should ensure:
To harvest the cane at peak maturity (i.e., avoiding cutting of either over-matured or under-matured cane)
Cutting cane to ground level so that the bottom sugar rich internodes are harvested which add to yield and sugar
De-topping at appropriate height so that the top immature internodes are eliminated
Proper cleaning of the cane i.e., removing the extraneous matter such as leaves, trash, roots etc.
Quick disposal of the harvested cane to factory
Several standard analytical methods are available to determine the peak maturity or quality so that the cane is harvested at right time. Without such analysis also several farmers take-up cane harvesting based on crop age and appearance. Sometimes farmers harvest the crop even before the crop fully matures due to necessity to supply cane to the mills early.
Likewise delays in harvesting are also quite common, particularly when there is excess cane area. To avoid such extremes harvesting should be done at right time employing right method. The following criteria enable harvesting of cane at right time adopting proper procedures:
Harvesting is done based on maturity (age) group. Farmers who grow a particular variety are usually conversant with the harvesting time. Even most sugar factories give cutting orders to farmers based on crop age. This is not a scientific method since, planting time, crop management practices, weather conditions etc influences maturity.
Yellowing and drying of leaves, metallic sound of mature canes when tapped, appearance of sugar crystal glistening when a mature cane is cut in a slanting way and held against the sun are some of the visual indices of assessing maturity of cane.
Important sugarcane quality parameters for assessing cane maturity are the juice Brix, pol or sucrose percentage and purity.
Juice Brix: Juice Brix refers to the total solids content present in the juice expressed in percentage. Brix includes sugars as well as non-sugars. Brix can be measured in the field itself in the standing cane crop using a Hand Refractometer. This is usually referred as a Hand Refractometer Brix or HR Brix. In the field using a pierce collect composite juice samples from several canes. Then place a drop of the composite juice sample in the Hand Refractometer and measure the Brix reading.
The circular field gets darkened relative to the Brix level, which could be easily read. The HR Brix meter has graduations from 0 to 32 per cent. The HR Brix readings can be separately taken from both top and bottom. A narrow range indicates ripeness of the cane, while a wide difference indicates that the cane is yet too ripe. On the other-hand if the bottom portion of the cane has lower Brix value than the top, it means that the cane is over-ripened and reversion of sugar is taking place.
Juice Sucrose Or Pol Per Cent: The juice sucrose per cent is the actual cane sugar present in the juice. It is determined by using a polarimeter, hence sucrose per cent is also referred to as pol per cent. For all practical purposes pol % and sucrose % are synonyms. Now a days an instrument called sucrolyser is also available for determining sucrose % in juice.
Purity Coefficient: It refers to the percentage of sucrose present in the total solids content in the juice. A higher purity indicates the presence of higher sucrose content out of the total solids present in juice. The purity percentage along with sucrose percent aids in determining maturity time.
Purity Percentage = (Sucrose %/HR Brix)100
A cane crop is considered fit for harvesting if it has attained a minimum of 16% sucrose and 85% purity.
Reducing Sugars: The reducing sugars refer to the percentage of other sugars (fructose and glucose) in the juice. A lower reducing sugars value indicates that much of the sugars have been converted into sucrose.
Commercial Cane Sugar: The commercial cane sugar (CCS) refers to the total recoverable sugar percent in the cane. This could be calculated by the following formula:
CCS (tons/ha) = [Yield (tons/ha) x Sugar Recovery (%)] /100
Sugar Recovery (%) = [S - 0.4 (B - S)] x 0.73
Where, S= Sucrose % in juice and B= Corrected Brix (%)
In many countries even today harvesting is done manually using various types of hand knives or hand axes.Among the several tools the cutting blade is usually heavier and facilitates easier and efficient cutting of cane.
Manual harvesting requires skilled labourers as improper harvest of cane leads to loss of cane & sugar yield, poor juice quality and problems in milling due to extraneous matter. (In the picture: Manual harvesting of sugarcane)
Harvesting labour is becoming scarce and costly in view of diversion of labour to other remunerative work in industry, construction, business etc. Mill stoppages because of non-availability of canes are not uncommon owing to shortage of harvesting labour. And, most of the new mills are of higher crushing capacity and many are expanding their crushing capacities. Therefore daily requirement of cane is increasing and hence greater demand for harvesting labour.
Added to this most of the present day agricultural labourers are not interested in field operations involving much drudgery. Thus in years to come, the labour position is likely to deteriorate further. Therefore mechanization is inevitable and hence, adoption of mechanical harvesting of cane in future is inevitable.(In the picture: Mechanical harvesting of sugarcane)
In countries like Australia, Brazil, USA, South Africa, Taiwan, Thailand etc where sugarcane cultivation is highly mechanized huge harvesters are employed for cane harvesting. In these countries, sugarcane is grown on large plantation scale in large farms owned by either mills or big farmers. The field capacity of mechanical cane harvesters varies with the size (2.5 to 4 ha per day of 8 hours.
The limitation of mechanical harvesters is use of such machines in small, irregular and fragmented holdings, diversified cropping patterns, limited resource capacity of small & marginal farmers in several countries.