Sugarcane is grown in the world from alatitude 36.7° N and 31.0° S, from sea level to 1000m of altitude or little more. It is considered as essentially a tropical plant. It is a long duration crop and thus it encounters all the seasons' viz., rainy, winter and summer during its life cycle.
Principal climatic components that control cane growth, yield and quality are temperature, light and moisture availability. The plant thrives best in tropical hot sunny areas. The "ideal" climate for production of maximum sugar from sugarcane is characterized as:
A fairly dry, sunny and cool, but frost free season for ripening and harvesting - moisture percentage drops steadily throughout the life of the sugarcane plant, from 83% in very young cane to 71% in mature cane, meanwhile sucrose grows from less than 10 to more than 45% of the dry weight.
Rainfall: A total rainfall between 1100 and 1500 mm is adequate provided the distribution is right, abundant in the months of vegetative growth followed by a dry period for ripening. During the active growth period rainfall encourages rapid cane growth, cane elongation and internode formation. But during ripening period high rainfall is not desirable because it leads to poor juice quality, encourages vegetative growth, formation of water shoots and increase in the tissue moisture. It also hampers harvesting and transport operations. This seems to be the case in regions of South America, South East Asia and some parts of Southern India.
Temperature: Growth is closely related to temperature. Optimum temperature for sprouting (germination) of stem cuttings is 32° to 38°c. It slows down below 25°, reaches plateau between 30°-34°, is reduced above 35° and practically stops when the temperature is above 38°.Temperatures above 38° reduce the rate of photosynthesis and increase respiration. For ripening, however, relatively low temperatures in the range of 12° to 14° are desirable, since this has a noticeable influence on the reduction of vegetative growth rate and enrichment of sucrose in the cane.
At higher temperatures reversion of sucrose into fructose and glucose may occur besides enhancement of photorespiration thus leading to less accumulation of sugars. Severe cold weather inhibits bud sprouting in ratoon crop and arrests cane growth. Temperatures lower than 0°C induces freezing of less protected parts such as young leaves and lateral buds. The damage depends upon the length of the cold period. Smut initiation and spread is high at ambient temperatures of 25° -30°. Similarly the spread of red not disease is high at higher temperatures (37°-400°) when all other conditions are similar. Rust incidence is high when the minimum temperatures are drastically reduced. Shoot-fly incidence is high in summer when the air temperatures are very high. Also higher shoot fly incidence was observed when the difference between maximum (day) and minimum (night) temperature are low.
Sugarcane is a sun loving plant. It grows well in areas receiving solar energy from 18 - 36 MJ/m2
. Being a C4
plant, sugarcane is capable of high photosynthetic rates and the process shows a high saturation range with regards to light. Tillering is affected by intensity and duration of sunshine. High light intensity and long duration promote tillering while cloudy and short days affect it adversely. Stalk growth increases when daylight is within the range of 10 - 14 hours. Increase in leaf area index is rapid during 3rd to 5th month, coinciding the formative phase of the crop and attained its peak values during early grand growth phase (Ramanujam and Venkataramana, 1999).
Optimum climatic requirements
Mean total radiation received in 12 months of growth has been estimated to be around 6350 MJ/m2. About 60% of this radiation was intercepted by the canopy during formative and grand growth periods. The total dry matter production showed linear relationship with the intercepted PAR and the test of correlation yielded R2 value of 0.913 (Ramanujam and Venkataramana, 1999).
However, the energy conversion rate in terms of dry matter production per unit of intercepted radiation showed a quadratic response with percent light interception indicating that the rate of energy conversion increased linearly up to 50% light interception and beyond this level, the rate of photosynthetic conversion of solar radiation gets reduced (Ramanujam and Venkataramana, 1999).
In sugarcane crop canopy the upper 6 leaves intercept 70% of the radiation and the photosynthetic rate of the lower leaves decreased due to mutual shading. Therefore, for effective utilization of radiant energy a LAI of 3.0 - 3.5 is considered optimum.
Areas having short growing period benefit from closer spacing to intercept high amount of solar radiation and produce higher yields. But in areas with long growing season wider spacing is better to avoid mutual shading and mortality of shoots.
Rough estimates show that 80% of water loss is associated with solar energy, 14% with wind and 6% with temperature and humidity. High wind velocities exceeding 60-km/hour are harmful to grownup canes, since they cause lodging and cane breakage. Also, winds enhance moisture loss from the plants and thus aggravate the ill effects of moisture stress.
Effect of climate on sugarcane yields and sugar recovery
The sugarcane productivity and juice quality are profoundly influenced by weather conditions prevailing during the various crop-growth sub-periods.
Sugar recovery is highest when the weather is dry with low humidity; bright sunshine hours, cooler nights with wide diurnal variations and very little rainfall during ripening period. These conditions favour high sugar accumulation.