Ratoon cropping is an old system which has been practised for many years, especially in the tropics. Although the origin of ratooning is probably not known for any particular crop, it may have begun when man first noticed regrowth of new shoots following cutting of certain crops at harvest, thus producing a new crop without replanting. Also, early man’s observations of grassland regrowth following burning might have created an interest in utilizing regrowth of plants as a basis for multiple harvesting from an original root system.
The word ratoon seems to have originated either from the Latin words retonsus – cut down or mown; or retono – to thunder back, resound; the Spanish – retono fresh shoot or sprout or even the French rejeton – sucker or shoot, scion, descendant, offspring or sprout. The first harvest of a crop is usually called the “plant crop”, and each succeeding harvest is designated “first ratoon,” “second ratoon,” and so on.
Sugarcane is considered to be mature and ready for harvesting if it attains over 18% (16% in sub-tropical zones) sucrose and 90% purity of cane juice. The varieties, which attain such level at 300 days of age, are considered as early varieties. If these parameters are reached by variety in 360 days, it is considered as mid-late. The main idea of maturity-based classification of varieties is to facilitate harvesting of variety at a proper time to enhance overall recovery and consequently the sugar production.
Extent of ratooning
In India, almost 50 per cent of the cane area is always under ratoons. The percentage of ratoon area is relatively greater in the subtropics than in the tropics. In India, raising one to two ratoons is most common, though there are instances of many ratoons or “multi-ratoons” in certain pockets of Tamil Nadu, Andhra Pradesh and Karnataka. In commercial planting, as already stated, one or two ratoons are most common in India. Many sugarcane growing countries raise several ratoons.
Cane yield decline in successive ratoons is a common phenomenon in most of the sugarcane growing countries of the world. A 10 per cent yield decline is considered quite normal. In several countries, ratoon yields are either same as plant crops or sometimes higher than the plant crops if managed properly. The average yield gap between plant and the ratoon crop in the country is 20-25 per cent. The gap is higher in the subtropical states. Because of the lower yields, even though ratoons occupy about 50 per cent of the cane area, their contribution to the total cane production is only around 30 per cent. Low ratoon yields are one of the reasons for the low average yield of the country. The major causes for yield decline in ratoons in our country are:
- ‘Free’ – or ‘gift crop’ attitude of the farmers towards ratoons and therefore poor ratoon
- Reduced initial population because of reduced stubble sprouting.
- The decline in the soil nutrient status.
- Soil compaction and poor soil physical status.
- More incidence of pests and diseases.
- Adverse weather conditions at the time of plant crop harvest, mostly in the sub tropics
Because of the ‘free crop’ attitude, most farmers neglect ratoons in all aspects of crop management, particularly, all monetary inputs are either not given or given in fewer quantities.
They are content with whatever the cane yield they get. They consider it as a ‘bonus’. But when we consider productivity regarding output per unit area per unit time, poor ratoons means a colossal waste of our land resources.
Stubble deterioration is a common cause for inadequate sprouting. In the subtropics, winter harvested crops do not give good ratoons because of lack of sprouting due to low temperatures. Late harvested canes also cause stubble failure due to high temperature. Under wet soil conditions, sprouting fails. Low sprouting may also be due to certain pests and diseases. It has been observed that from white woolly aphid affected plant crops, ratoon sprouting is seriously affected, even total failure has been noticed.
Decline in soil nutrient status
The plant crop stands in the field for a minimum of one year. During that period it experiences at least one rainy monsoon season. Also, large quantities of irrigation water would have passed through its root zone. Therefore, by the time the plant crop is harvested, the soil gets depleted of nutrients due to crop uptake and losses of applied and native nutrients through leaching and other means.
Soil compaction occurs due to irrigation, movement of animals and humans as well as machinery. Compaction due to machines is practically nil or insignificant in our country as almost all operations are manually carried out. Soil compaction (increase in bulk density) Leads to poor soil aeration and reduced water holding capacity. It affects root growth severely. This is why ratoon root system is always less extensive than the plant crop, particularly under inadequate crop management.
Pests and diseases
Ratoons, in general, are more prone to pest and disease attack as they are weak and less vigorous in most situations. Three diseases, viz. the RSD, GSD and smut are more severe in ratoons than the plant crops. Several insect pests are also more in ratoons.
- Sugarcane Breeding Institute, Coimbatore-641 007