In this article we will discuss about the growth and development of sugarcane.
Root System:
The early growth of sugarcane roots has been described by Clements 1980. Under favourable environment, the auxiliary buds on setts become active within three days of planting and sett roots begin to grow from root band at the base of the internode. Sett roots grow at a maximum rate of 24 mm day-1 and stop elongating when they are 150 to 250 mm long.
They turn dark, decompose and disappear within two months after planting. Shoot roots begin to grow from the short basal internodes of the shoot at about the time it emerges from the soil. First shoot roots are much thicker than sett roots, rate of growth more rapid, produce few branches and penetrate the soil at a steep angle.
Shoot roots produced later are finer and branch more freely than earlier shoot roots. Their maximum growth rate is 75 mm day-1 for periods of 1 to 2 days or 40 mm day-1 when their growth is averaged over a week. Short irrigation intervals encourage roots to develop near the soil surface. Root system on sandy soil tends to be finer, highly branched and deeper than that growing in heavy soils.
Shoot System:
Maximum dry matter accumulation occurs only with near optimum temperatures, high solar radiation, complete ground cover and minimal nutrient and water stress. Under these conditions, short term (1 to 2 months) production of above ground mass can reach 40 to 44 g m-2 day-1.
Incomplete interception of light during canopy development, low solar radiation, suboptimal temperatures, reduced growth during ripening and a variety of soil and biotic stresses typically reduce full season growth rates of commercial field and experimental plots to 6-23 and 20-32 g m-2 day-1 respectively.
Sugarcane has the capacity to tiller rapidly. Stem number increase exponentially with time until a maximum of 20 to 30 stalks m-2 is reached at 4 to 6 months. The LAI increases in a similar manner. When the LAI approaches 2-3 at 4 to 6 months, many younger tillers begin to die and tiller number normally stabilises at 10 to 20 stems m-2.
Several studies suggest that the maximum LAI for sugarcane is 7 to 8 m-2 leaf m-2. This value is attained only in vigorously growing canopies of erect cane. The LAI typically declines as the crop approaches harvest maturity, especially when nitrogen and water stress or chemical ripeners are used to slow expansion growth and increase sugar storage in the stem.
Gascho and Shih (1982) divided sugarcane vegetative growth into four stages: germination- emergence, tillering-cnopy establishment, grand growth and ripening. Duration of the stage is highly dependent on climate. Low temperatures or drought stress can delay germination, emergence and tillering and canopy development.
In subtropical climates, the first two stages may last up to 5 months and adequate water and nutrients can promote vegetative growth leading to delay in ripening. In Hawaii, where the crop is grown for more than 2 years, providing adequate irrigation and nutrients until the crop is 20-22 months old can extend the grand growth period.
The rate of cane elongation during night is, generally, greater than during day time. Growth rate during monsoon (July-October) will be much higher than in other months in India. Between eksali and adsali crops, rate of growth from May to September is much higher in the former, even though, from the point of total height, adsali is superior.
Cultivars with high yields have higher LAI, LAD and LAR. The LAI for cane growing in Peninsular India ranges from 4 to 8 with a ceiling around 6 during bloom phase. The CGR vanes from 21 to 53 g g-1 wk-1. The NAR ranges from 0.34 to 0.63 g dm-1 wk-1. The specific leaf area ratio varies from 0.29 to 0.31 dm-2 g-1. The LAD ranges from 265 to 285 days for a 12 months crop.
The dry matter production ranges from 20 to 50 g m-2 day-1. The biomass yield in tropics is 80-100 t ha-1 while in subtropics it is 40-60 t ha-1. Many progressive farmers in tropical India have achieved yield levels of 250 t ha-1 yr-1 or even more. The major yield attributes are number of millable canes, cane length, girth and weight per cane.
Yield Potential:
At maximum photosynthetic efficiency of leaves and under ideal conditions of growth, sugarcane could yield 364 t ha-1 of green stalks. The yield could increase further (473.2 t ha-1) if 30 per cent weight of the trash biomass is also included in it.
Yields to this order have actually been harvested under ideal conditions of Hawaii and other countries where optimum growing conditions with regard to temperature, humidity, moisture and nutrients are ensured.
To realise maximum possible yields of sugarcane, about 180-200 thousand millable canes ha-1 each of 2 kg weight are required. However, at present only about 100 thousand millable canes ha-1 each weighing 0.6-1.0 kg weight are obtained under varying conditions of cultivation.
Therefore, there is scope to improve cane productivity by increasing millable canes per unit area by developing appropriate agrotechniques to sustain high density shoot population per unit area.
Flowering:
Most sugarcane cultivars are considered short day plants. Time of initiation of flowering largely depends on the location of the place where the plant is growing. Broadly speaking, in the northern hemisphere (India), canes flower from about October till December. In the southern hemisphere (Australia), canes flower in the period April-May. In Columbia, which is very near to equator, flowering occurs every month, though sparsely.
Duration of day length is the major factor controlling flowering (arrowing). Flower initiation is under the control of a stimulus called florigen generated in the leaves and translocated to the flower bud. At Coimbatore, four hrs. extra dark treatment daily from June eleventh to plants planted in February first week made a large number of early and late flowering varieties to flower simultaneously as early as September.
Sugarcane could be either forced to remain vegetative by extra light treatment or induced to flower at will at any time and even throughout the year by subjecting the light treated plants to four hrs. extra dark treatment.
Flowering can be suppressed by removal of the spindle, spraying chemicals such as Maleic hydrazide, Diquat, Paraquat etc. In parts of Andhra Pradesh and Maharashtra, the adverse effect of flowering is mitigated by changing planting time. Sugarcane planted from July to September (adsali) will not flower in the same year and hence has long vegetative period over 12 months leading to higher yield over eksali crop which flower in the same year of planting.
Versene (2.25 kg ha-1) after third week of September can reduce the flowering. Diquat spray (1.5 kg ha-1) is very promising in Hawaii. It reduces flowering from 70 to 2 per cent. Among the other cultural methods, withholding irrigation at flower initiation is effective in minimising flowering.