Sugarcane-Biology, Agriculture and Ecology
By Dr. Yashpal Singh
From the Executive Summary of book entitled “Sugarcane and Sugar-Biology, Agriculture, Manufacture, Regulation, Environment and Pollution Control”, 2024 by Dr. Yashpal Singh. Published by The Wealthy Waste School India and U.P. Sugar Mills Association. Available at: https://www.amazon.in/Sugar-Cane-Agriculture-Manufacture-Regulation/dp/936039856X/ref=sr_1_1
With a cultivation history of more than 8000 years, Sugarcane has evolved as a major cash crop and a source of multiple products including Gur (Jaggery) and Sugar. Cultivation of Sugarcane in India dates to the Vedic Period (1400-1000 BC). India, as of 2019, contributed to 18.18% of the total area under cane globally. Sugar appears to have been derived from sugar cane in India about 2000 years ago and since then the demand of specialty sugar is constantly on the rise. The production of Sugar by boiling cane juice first look place in India most likely during first millennium BC. India and Brazil produce about half of the Global Sugar Production with S. officinarum accounting for 70% of the worlds sugar. Sugar Cane is also a source of ethanol and is grown in over 100 countries. The per acre yield of Sugar cane ethanol is almost twice as that of maize ethanol. The therapeutic and cosmetic properties of Sugarcane and sugar paste are well documented. The area under sugarcane cultivation in India has increased from 1.7 million hectares in 1950-51 to 5.2 million hectares in 2020. India is the second largest producer and the largest consumer of Sugar in the world. Along with maize, wheat and rice, sugar cane accounts for half of the global crop primary productivity.
In India sugarcane is grown in both tropical and subtropical regions. The productivity of Sugar cane in the tropical belt is 26.4% higher than the subtropical belt. Some typical constraints in the cultivation of sugar cane in India are the non-availability of labor, inadequate transportation, high costs of Sugar cane seed setts, pest and disease infestation, extremes of climate, regional politics, lack of adequate scientific knowledge, flooding, drought, non-availability of suitable equipment’s, lack of technical guidance and lack of training. The first Vacuum Pan Sugar factory for producing cryptal white Sugar was get up in 1903 in the State of Uttar Pradesh. 516 Sugar Mills over India, crushed Sugar Cane during 2021-22 producing 394 lakh metric ton of Sugar and of which 35 Lakh metric tons was diverted for ethanol. As against a total LOI quantity of 413.33 crore liter, 113.17 Crore Liter of ethanol have been supplied as on 13-03-2022 of which 86% has been made from Sugar Cane Juice/B heavy molasses. The country on an average has achieved a blending percentage of 9.45% till mid-March since December 2021. India exported 109.8 Lakh metric Tons of Sugar during the Sugar season 2021-22 which was likely to go up to 112 Lakh Metric Tons and expected to improve the liquidity of Sugar mills and to allow them to pay the cane arrears.
For India the cost of cultivation of sugar cane (2019-20) works out to be Rs. 129 per quintal at 10% recovery after accounting for the actual paid out costs plus cost of family labor and the rental value of held lands. At an all-India level the gross returns over the actual paid out cost plus family labor has been estimated as 131% with U.P., Uttarakhand and Karnataka having the highest returns.
Sugarcane belongs to the genus Saccharum of the grass’s family. The taxonomy and phylogeny are complicated as plants from 05 genera show common characteristics and form a closely related inter breeding group known as the Saccharum Complex which includes the genera Saccharum, Erianthus section Ripidium, Miscanthus Section Diandra, Narenga and Schlerostachya. Saccharum officinarum has a high sugar content but is very susceptible to diseases and Saccharum spontaneum has less of sucrose but is highly resistant to pests and diseases. Saccharum officinarum the principal source of cane sugar has evolved as a result of a complex transfer of genes between ancestors of S. spontaneum, Erianthus arundinaceous and Miscanthus sinensis or from S. robustum as a result of hybridization and constant back crosses. Saccharum spontaneum is often considered as a weed species as it reduces the productivity of other crops.
Sugar cane can reproduce both sexually and asexually. Sexual reproduction is through true seeds bearing soft hairs. Asexual reproduction which has been of more use in sugar cane cultivation can be achieved through nodal buds found on setts, through rhizomes or through stools. Flowering, triggered by the interaction between genotypes and environmental factors may be regular or sporadic. The initiation of flowering may adversely affect yields and reduce the sucrose content of the stalks. Flowering uses both energy and sugar and is not desirable.
Sugar cane is a C4 plant hawing a highly efficient system of storing solar energy and producing huge amounts of biomass over the germination, tillering, grand growth and the maturity and ripening phases. Because of the high amount of Biomass produced the cane crop depletes the soil of essential nutrients. An average crop of Sugar cane yielding 100 ton/ha removes 208 Kg of nitrogen, 53 Kg of Phosphorous, 280 Kg of Potassium, 30 Kg of Sulphur, 3.4 Kg of Iron, 1.2 Kg of Manganese and 0.6 Kg of Copper from the soil which has to be replenished to maintain the productivity of soil. Apart from bio manures and chemical fertilizers, green fertilization is also practiced where plants are cultivated for the purpose of incorporating them into the soil. Well defined inter cropping practices may also enhance crop productivity. Vinasse or Distillery spent wash can replace potassium fertilizers. It also contains major plant nutrients like phosphorous, Calcium, Magnesium, Sulphur, Zinc, Iron, Manganese, Vitamins, growth promoters and can be a useful soil fertilizer through pre-sown land application.
Planting and Agriculture
Commercial sugarcane is propagated vegetatively through whole stalks or setts also known as billets, seed pieces or seed canes. It can also be propagated by ratooning which allows the regrowth of the stems of the stools that remain in the soil after harvesting. Invitro meristem cultures are also employed to produce high quality seed cane. Thin cell layer cultures of immature leaf or inflorescence tissue can also be used directly for regeneration of plants. Breeder seeds are reared in experimental farms and supplied to farmers. The Government of India has formulated sugarcane seed certification standards. Seed certification in India is voluntary and labeling is compulsory.
It has been suggested that alkaline, saline or water logged soils should be avoided as sugar cane nurseries and seeds should be adequately prepared and treated to prevent attack of pathogen and diseases for improved germination and yield.
Sugar cane takes about one year to mature (Eksali) in subtropical parts of India whereas it may take about 18 months to mature in the Tropical states and is called Adsali. Planting time in India is usually October to March or September to April. It grows on a wide variety of soil types including clay, sandy and clay loams, acidic volcanic soils and sedimentary soils. In addition to adequate soil fertility, it requires high temperature and high irrigation/rainfall. Germination is slow at lower temperatures (180C) and increases rapidly to about 350C. The field is deep ploughed after harvesting and then followed by light ploughing to produce a well aerated soil with good water holding properties. Occasionally in some parts of India (particularly North) one pre-planting is given for seed bed preparation followed by ploughing.
Setts are generally planted in rows with suitably assigned inter row spaces within a few days of harvest of cane. Sugar cane is a water intensive crop and the yields are much higher when the crop is supplied with adequate water. Between 89-118 Kg of water has been reported to be required to produce 1 Kg of Sugar cane. A number of planting methods like the flat method, ridge and furrow method including earthing up trench method, the furrow irrigated raised bed method, spaced transplanting method, the ring pit method etc. are generally practiced.
Sugar cane is also often grown in rotation with other crops. This rotation helps in reducing the buildup of diseases and provides nitrogen for the next crop. Crops may be planted within rows of sugar cane. Apart from paddy and legumes some short duration fast growing crops, which do not exert a major shading affect, can be gainfully used for intercropping. In addition to the biological advantages, they may serve as an additional source of revenue to farmers. In order to prevent cane lodging the clumps of canes are bound together by dried up leaves.
Germination
In the initial phases of germination, ‘sett roots’ are produced from the root primordial around the nodes of the ‘sett’. These are temporary roots and help in maintaining the moisture content of the ‘setts’. They die off once the ‘Shoot roots’ start developing from the new buds and root primordial on the nodes in the primary shoot. Further plant growth is supported by the shoot roots. Shoot roots are permanent, thick fleshy and less branched and continuously produced from tillers from the base of new shoots, 5 to 7 days after planting. In the initial stages, stem elongation is rapid but the sugar content is low but in the maturity phase, the vegetative growth slows down and the Sugar content rises. During stem growth, each internode acts as an independent unit in terms of vegetative growth and sucrose accumulation and continues to do so as long as the green leaf is attached. Maturation of stem is affected by age, nitrogen status and moisture while the accumulation of sucrose can be influenced by water stress, nutrient status and temperature.
Mechanisation
A number of planting implements are being used to assist the planting operations including preparation of soil (making Furrows, trenches or pits), sett cutting, placement of setts, fertilizer application, fungicide, insecticides and termiticides applications and covering and pressing of setts. Deep Furrow Sugar cane planters, Sugarcane trench planters, pit diggers, mechanized inter crop planters ratoon management device, Sugar cane sett cutter, Sugar cane de-trasher, Sugar cane inter-cultivator, earthing up ridgers, sugar cane stubble shavers, ridgers cum weeders, rotavator, sugar cane combined Harvester and Sugar bud chipper are some mechanical devices available in the market.
The production of Sugar cane is sensitive to a number of constraints which include the ill effects of continued monocropping, resultant nutrient imbalance and decrease in soil carbon, excess fertilization, a high mortality rate of tillers in ratoons and a higher incidence of pests and disease in ratoon crops. Abiotic factors like drought and high temperatures, flooding, water logging and depleting water resources may also influence adversely the yield of sugar cane.
Other Cane Products
Apart from sugar and ethanol, sugar cane is also important in the production of sugar cane juice, muscovado sugar, jaggery or gur, sugar cane syrup, rapadura, other direct fermentation products, livestock feed, sugar cane tops for livestock, bagasse, molasses, filter cake and vinasse. Raw Sugar which is obtained from the clarification of the sugar cane juice with lime and subsequently concentrating it to produce ‘massecuites’ which is mixture of crystals and surrounding dense molasses is more nutritive than white sugar.
Sugar cane is an excellent feed stock which can be readily turned into fuel. For every ton of cane crushed a mill can produce 115 Kg of Sugar and 45 Kg of molasses (18 Kg of Fermentable Sugar) that would give 10.8 liters of ethanol. The Government of India has come up with a National Bio Fuel Policy on Bio fuel and has fixed a target of 20% ethanol blending with petrol and 5% biodiesel blending with diesel by 2025-26. Oil manufacturing companies have already achieved 10.16% blending as on 10th, July 2022.
Bagasse is also an important product from sugar cane. The rich content of cellulose fiber makes it ideal for use in the pulp and paper industry, for manufacture particle Boards, in cogeneration as a fuel, as cattle feed, as a substrate in the culture of mushrooms and in the production of furfural. Being an effective bio sorbent, it can be used in waste water treatment and used effectively in adsorbing chromium, nickel, cadmium and dyes. Sugar cane species, suitably selected, on their total biomass content rather than sugar contents, can serve as an important source of renewable energy. Saccharum spontaneum which is rich in fiber but low in sugar offers promises.
Molasses with a high Sugar content (45 to 55%) are a very promising raw material for distillation, for acetic acid plants, for fuel alcohol plants, for the generation of biogas, in cattle feed, for ethyl alcohol production and the production of baker’s yeast, lactic acid, citric acid, glycerol, butane, acetone, monosodium glutamate, ephedrine hydrochloride etc.
Black strap molasses is a source of calcium, magnesium, potassium and iron. One table spoonful will fulfill almost 20% of the daily requirements of these nutrients.
Sugarcane and its products are widely used in folk medicine, in the manufactures of yeast, (with 4 kg molasses producing 1 Kg yeast), in the manufacture of sugar syrup, sugar candy and confectionary. Sugar Cane Trash is used as a mulch in the fields and in Gardens or as low-grade cattle feed. In India equipment has been developed to turn trash into solid briquettes for use as fuel. Sugar cane tops serve as a good source of animal feed. Sugar cane wax can be used in the production of cosmetics and pharmaceutical products. Press mud or filter cake is very rich in nutrients and may be used as manure or in the production of bio manure after aerobic composting with spent wash from distilleries. It is estimated that 1 ton of sugar cane crushed produces 0.01 ton of Sugar Cane ash and 0.05 tons of press mud which is used as fertilizer.
Irrigation and Water Stress
Sugar cane is a water intensive crop. The water requirement per Kg of Sugar cane varies state to state depending on the number of irrigations required which could be anywhere between 6 to 8 in Sub-tropical regions and 20-36 in the topical regions. Poorly irrigated crops may exhibit a decrease in flowering, decrease in the length of the internodes, decrease in the amount of sugar but an increase in fiber percentage, a decreased rate of germination and a decrease in sugar yield. Water logging should be avoided as it creates a serious stress on root respiration, nutrients tend to leach down, microorganism activity is reduced and excessive branching is initiated leading to lodging of cane. On the other hand, drought is also regarded as the most significant abiotic stress and water deficits may result in about 60% productivity losses globally.
Plants suitably adapt drought resistant strategies including changes in life style, modulation of growth and development and regulation of plant functions to balance resource allocation. A number of steps like early planting, a wider inter row spacing in planting, treatment of setts and soil, better irrigation practices, trash mulching and use of drought resistant varieties etc. have been also suggested to manage drought stress.
The cultivation of Sugar cane, being water intensive, exerts a great pressure on the water resources of the country. The Niti Aayog has suggested moving out at least 3 lakh hectares currently used in sugar cane cultivation to other crops and the farmers suitably subsidized. An initial compensation of Rs. 6000 per ha has been suggested. It has also been suggested that sale slips issued to farmers for cane should be restricted to just about 85% of their land holdings in order to further incentivize the shift.
A number of irrigation methods are currently practiced. These include flood irrigation, furrow irrigation, alternate skip furrow irrigation, drip irrigation including the surface and sub surface irrigation practices. Of these drip irrigation is the most promising as it ensures uniformity in application (90%), saves about 25 to 50% water, is associated with lowered evaporation losses and low weed and pest incidence.
The irrigation systems may be variously classified as flood irrigation, large furrow systems, Wakhura systems, contour furrow system, serpentine method, alternate skip furrow method, sprinkler irrigation, fertigation, flood irrigation. In case of furrow irrigation wetting patterns have to be suitably designed based on soil types. An ideal wetting pattern is one where the wetting zones overlap each other and there is an upward capillary movement of water that wets the entire ridge and supplies the root zone with water. The zone of planting on the ridges and furrows is also important. While planting on the top of the ridge may impart protection against water logging, planting in the furrow may protect against water scarcity, planting on the side of the ridges may protect against accumulation of salt and planting on the sunny side of the ridge may boost the winter and early summer crop.
Micro irrigation systems like sprinkler irrigation with drip irrigation and mine sprinklers, micro sprinklers, bubble irrigation and a proper well designed irrigation schedule are very beneficial in managing crop yields and water stress.
Harvesting
Harvesting of Sugar cane is indicated by the onset of yellowing of the leaves, cessation of growth, emergence of arrows, production of metallic sound from canes, a swelling of buds and sprouting of the eyes. Cane in North India matures in 10-12 months whereas it may take 18-20 months in South India. Cane has to be harvested close to the ground (3 to 5 cm above) in order to utilize the high sugar content of the lower nodes. The cane should be properly cleaned of leaves, trash, root etc. Sugar cane is harvested when its sucrose content is the highest (generally 16% with 85% purity) and the glucose and fructose content are at their lowest.
Sugar cane can be harvested mechanically, sub-mechanically or is hand cut either green or burnt. Green harvesting is more common. Cane should be preferably crushed within 24 hours of harvesting to avoid deterioration due to moisture and sucrose losses. Harvested cane should be covered with trash and sprinkled with water to prevent water loss. Manual harvesting may be performed with hand knives, cutting blades or hand axes through skilled labor. Skilled harvesting prevents the loss of cane juice, juice quality and sugar and also keeps the place clean. Mechanical harvesting is also practiced through mechanical harvesters which help in removing the leafy tops of canes, cutting the stalks into small pieces (billets) which are also loaded in bins provided with harvesters. Tractor operated mechanical harvesters are also available.
Post harvest ratoon management is important for better yields. Ratooning is the cultivation practice of two harvests in one cropping season by producing a second crop from the original stubble. In case of a ratoon, the trash should be collected before burning, adequate stubble shaving should be done for uniform sprouting and old roots should be cut. Well maintained ratoons give higher yields. Proper irrigation, weeding and earthing up may be required for good ratoon crop management. The ratoon crop matures one month prior to the plant crop. Conventionally ratoon crop are maintained for two seasons but some farmers may be able to achieve 5 to 6 ratoon crops and follow the sustainable sugar initiatives. A ratoon management device has been developed by the I.I.S.R. Lucknow which works as a stubble shaving, subsoiler and ridge making device and can accomplish harrowing, weeding, dispensing farm yard manure, pesticides, fungicides, fertilizer and earthing up in one pass.
Trash Management
About 10 to 12 tons of dry cane leaves are produced per hectare of cane crop. Trash management generally involves trash farming, trash blanketing, trash mulching, use as fuel in boilers (where it may achieve a more than 30 times reduction in CO emissions and as fodder for livestock. Trashy cane causes a decline in sugar production. Trash is often burnt also but using trash as mulch is a more favorable option. Trash farming helps in augmenting yields by 20% in the first ratoon and 30% in the second ratoon. It also improves soil tilth, contributes to the nitrogen regime, conserves soil and soil organic matter by preventing soil erosion, may lead to an increase of 43% in net returns in the first ratoon and costs 10% less to produce 1 ton cane, saves on chemical fertilizers and costs of new crop establishment and also helps in elimination of the health hazards associated with air borne emissions. A plant residue shredder has been developed by the IISR, Lucknow for trash shredding in the field. Burning trash in the field after harvesting is a common practice which assists in the destruction of harmful diseases and insects and also helps in providing a certain amount of potassium and phosphorous for growth. It also reduces the harvesting and handling costs but exert a significantly higher impact on air pollution and a loss in nutrient contents of trash. Trash mulching on the other hand helps in conserving soil moisture, in soil protection (erosion or nutrient leaching), in controlling weeds, increasing nitrogen fixation and total carbon. Ratoon crop productivity has also been observed to increase with trash mulching. Every ton of trash may contain 5.4 Kg of nitrogen, 1.3 Kg of P2 O5, 3.1 Kg of K2O and small quantities of micronutrients. Integrated Sugar cane trash management achieves a significantly higher yield of cane and is practiced by irrigating the plot to completely soak the trash to soften it for easy handling, mulching trash rows alternating with un-mulched ratoon rows, applying nitrogenous fertilizer to reduce the C:N ratio, applying farm yard manure with microbial culture (Trichoderma viridi), stubble shaving, shoulder breaking, gap filling and following the recommended ratoon management practices. Trash mulching also achieves a better germination and an early maturity.
Chemical and organic fertilizers
Nitrogen is required for improved yields and sugar content. Nitrogen deficiency may produce thin, stunted canes with necrotic leaves and reduced root mass. An excess of nitrogen may prolong crop maturation and produce plants with excessive root canopy making it susceptible to insect pests. The amount of sucrose can come down because of excess vegetative growth.
Phosphorous deficient plants may also exhibit thin stalks and stools and a poor root system. Excess phosphorous may lead to a deficiency of other trace elements such as zinc an iron and reduce sugar yield.
Potassium helps in the translocation of sugars. Deficiency leads in depressed growth, yellowing of leaves and ultimately death while an excess reduces the recovery of sugar and a deficiency in other trace elements.
Calcium regulates soil acidity. A deficiency may lead to leaf chlorosis and reduction in stem diameter. Increased soil acidity may lead to toxicity.
Magnesium is required for the synthesis of chlorophyll. A deficiency results in yellow leaves and reduced diameter with an internal browning. Other microelements like iron, aluminum, zinc, copper, boron, silicon, molybdenum and manganese may be required and influence cane growth.
Green Manure Crops complimented by nitrogenous fertilizers reduce the nitrogenous fertilizer requirements of Sugar cane. Due to a ramification of roots, inter cropping may help in preventing the leaching of nitrates. Filter Press mud is also a good source of N, P and K when bio-composted with sugar cane trash, cow dung or distillery spent wash. Bio-fertilizers both nitrogen fixing bacteria, phosphorous solubilizing bacteria or cellulose decomposing micro-organisms have been found to reduce the requirement of chemical fertilizers by 25% which in turn reduces soil degradation.
Integrated nutrient management (INM) comprises the intelligent use of organic, inorganic and biological resources to sustain optimum yields, improve and maintain soil chemical and physical properties and provide nutrition packages that are technically sound, economically attractive, practically feasible and environmentally safe. It integrates organic, chemical and biofertilizers to optimize yields. Soil fertility can be managed efficiently through an initial testing to determine nutrient and water requirements and to draw up cropping plans, nutrients application time tables for increased uptake and plans to ensure minimal leaching. A good management plan would also provide for ensuring the availability of nutrient to the plant roots, reducing losses due to volatilization of ammonia, erosion and run off. Foliar application during drought and fertigation with drip irrigation, use of organic and animal manures, reduced used of inorganic fertilizers, crop rotation, inclusion of legumes in the cropping system, reducing erosion and adoption structured controls to prevent erosion are also some good practices associated with integrated nutrient management for sugar cane.
Climatic Factors influencing Sugar Cane
Temperature, rainfall and humidity play an important role in the growth and yields of sugarcane. A rainfall range of 1800 to 2500 mm per year, rightly distributed, is ideal for sugar cane. Dry weather with low humidity, bright sun shine hours, cooler nights with a wide diurnal variation and very little rainfall during the ripening phase favors high sugar accumulation. Very high or very low temperatures deteriorate the juice quality. The optimum temperatures during germination are between 260C to 330C and about 200C during maturation low temperatures may impact sett germination, growth, flowering seed germination, yields, sucrose content and susceptibility to infection. Growth slows at temperatures above 400C with lower sucrose contents. Warm and humid climates favor insect pests and diseases which influences the juice yield and sugar content. There are two basic agroclimatic regions for sugar cultivation in India. The tropical zone consists of the peninsular and coastal regions of India while the sub-tropical region comprises of the Northern States. About 55% of the cane in India is grown in the Sub-tropics. S. officinarum grows best in tropical areas but can also grow in sub-tropical areas. Greater solar radiation (7 to 9 hrs. of bright sunshine) favors higher sugar yields.
High winds may cause a lodging of cane stalks in fields leading to harvesting problems, reduced cane yields and reduced sugar content. Rat damage, suckering and stalk and stool death are also related to lodging. Lodging may also lead to reduced light interception.
Climate change predicted impacts may cause a 10% to 30% reduction in yield of sugar cane along with increased competition from weeds, increased incidence of diseases and a reduction in sucrose content. It has been recommended that adaptation strategies should focus on increasing sugar cane tolerance to warmer temperatures during winters, especially during the harvesting phase. Stress resistant and high yielding cultivars need to be developed. Alternative system of irrigation should be put in practice. The carbon sequestering potential of sugar cane (22 to 30 tons carbon/ha) is much more as compared to other pastures (3 to 8 tons carbon/ha). Blending ethanol brings down the green house gas emission also. The carbon dioxide absorbed in producing sugar cane is more than the CO2 produced by burning bagasse. Cogeneration is a viable option.
Biotic Factors and Sugar Cane
Pests and Pathogens have a significant effect on the growth and yield of sugar cane. A decline of 20% in sugar cane production because of insect pests and 19% by disease has been reported. Sugar cane may be infested by about 288 insect pests of which about two dozen may cause severe damage to crop and quality. Of particular significance are the Nematodes, Borers, Sugar cane thrips, cane grubs, corn wire worms and many vertebrae pests.
Weed infestations have been responsible for a 12% to 72% reduction in sugar cane yield. Uncontrolled weeds may remove 160 Kg nitrogen, 24 Kg Phosphorous and 203 Kg of Potassium from 1 Hectare of land. There are reports that weeds remove more than double the amount of NPK than taken by Sugar cane crop during the first 50 days. Weed infestations may be aggravated by wide row spacing’s, slow germination, heavy fertilization, frequent irrigation and increased competition for resources. Removal of weeds has been observed to increase two fold over the untreated plots. Ratoon yield also improves on removal of weeds.
Some common weeds are Cyperus rotundus, Cynodon dactylon, Commelina benghalensis, Cleome viscosa, Coccinia indica, Lipiandiflora, Ectipta alba, Ipomea aquatica, Chenopodium album, Convolvulus arvensis, Amaranthus viridis, Portula oleracea, Trianthema portulacastrum, Sorghum halepense, Sporobolus diander, Boerhaavia diffusa, Ageratum conyzoides, Erechtitis valerianifolia, Micania micrantha, Colocasia sp., Panicum spp. and Dactyloctenium aegyptium. A few weeds like Striga sps., and Orobanche sps. may be parasitic on the Sugar cane crop. Weeds can be removed mechanically through deep ploughing and hand weeding. Hoeing is a common practice in weed removal which not only controls weeds, but also promotes tillering. Crop rotations, crop competitions, clean cultivation technologies and mulching are also practiced for weed control. Herbicides are also used. The Central Herbicide Board has approved only a few herbicides like 2,4-D Dimethyl amine, 2,4-D Na salt Technical, 2,4-D Ethyl Ester, Diuron, Meta sulfuron Methyl, Hexazinone, Sulfentrazone, Clomazone (individually or together) and Halo sulfuron methyl at recommended does.
Various biological agents like bacteria, fungi, viruses and phytoplasma may cause damage to sugar cane leading to huge losses. These may be transmitted by harvesting implements/machinery and transmitted to further cuttings by blades. Disease free planting methods like soaking in hot water may help. Some important bacterial diseases are the ratoon stunting disease, the leaf scald disease. Many bacteria help in biological nitrogen fixation and in the defense against other sugar cane pathogens.
Fungal and Oomycete infections are responsible for the orange and ‘brown’ rust diseases which have been known to cause great losses in sugar cane yields. These diseases are controlled by using resistant cultures. Sugar cane smut caused by wind borne spores of Ustilago scitaminea has been observed to lead to yield losses from 30 to 100%. Control is achieved by using resistant cultivars, using uninfected seed canes and removing infected crops, compulsory plough out (if more than 10% crop is infected), or application of pre plant fungicide treatment and rogueing of infected plants.
Viral diseases like the ‘Chlorotic streak’ the ‘Fiji leaf gall’, ‘Sugar cane mosaic’, ‘Sugar cane yellow’ viruses are also of great concern.
Phytoplasmas are small wall less prokaryotes which may cause diseases like the Sugar cane white leaf disease, the sugar cane grassy shoot disease, the sugar cane yellow leaf syndrome and the Ramu stunt disease. These are transmitted through insect vectors.
Edaphic Factors
Soil plays a major role in the yield and productivity of sugar cane. Deep well drained medium texture soil with sufficient water holding capacity and a pH of 6.5-7.5 is most suitable for sugar cane. Sugar cane is also sensitive to soil salinity which adversely impacts the yield and sucrose content. The soil should be free of chemicals and metal toxicities, should have optimum levels of organic matter and salt concentrations with an adequate supply of plant nutrients, good drainage, moisture retention, a small population of pathogens and insect pests and a large population of beneficial organisms. The preferred depth of ground water is 1.5 meters with a recommended water content of 150 mm/m.
Some typical soil constraints are permeability issues, sub soil hardening, surface crushing, soil compaction, soil acidity and alkalinity, poor fertility, calcareous soils and low soil organic matter. Suitable techniques are available to restore the properties of ameliorated soils. Provision of adequate drainage, application of sand or coarse soil, application of organic manures and using water logging resistant varieties help in increasing soil permeability while excess permeability issues can be restored by roller compacting or application of clay with green manure. Chisel ploughing with application of organics helps in managing sub soil hardening and prevents movement of clay to lower layers. Surface crust can be broken up by ploughing and adequate green manuring and also by scraping surface soil. Controlled movement of heavy machinery in terms of weight, passes and location should be practiced in order to avoid compaction of soil. Soil salinity can be managed by leaching excess soluble salts. Sodic lands can be reclaimed by addition of suitable amendments like gypsum, phosphor-gypsum, press mud, distillery spent wash. Soils which are less fertile have to be augmented for deficiencies.
Environmental Allergens and safety
Sugar cane pollen is the most significant air borne allergen as compared to rice and other plant species. Apart from this it does not present any food related allergic reaction. Fungal exposure through organic dusts from mold infected sugar cane may cause a lung disease called as bagassosis. Anti-nutrients and toxicants which influence the palatability and nutrient acceptability of sugar cane for human and animal consumption are not reported in sugar cane. There is an unconfirmed report that sugar cane contains the Cyanogenic glycoside, ‘Dhurrin’ but the excessive processing of sugar cane reduces the level of Dhurrin and the risk of any exposure to Hydrogen Cyanide through consumption of sugar cane by animals and humans. Fresh sugar juice for human consumption should be taken soon after extraction as it is rapidly oxidized. This oxidation, caused by Polyphenol oxidase can be reduced using thermal and chemical pretreatment and increase the shelf life. Sugar cane bagasse has also found use as a source of dietary fibers for human consumption. The low digestibility of sugar cane because of high fiber content is one antinutritional aspect for mono-gastrics and ruminants and can be amended by supplementing with richer nutritional feeds or has its composition improved by addition of nitrogen and Sulphur salts during feed formulation. The digestibility can be improved by adding sodium hydroxide and other physical, chemical and biological pretreatments. Sugar cane juices and molasses are often also fed to animals but may produce side effects. Sugar cane plants also contain hydrocyanic acid. Unrefined sugar is toxic to horses.
Disease Management in Cane
More than 125 diseases have been reported for sugar cane globally. In India, about 10 to 15% of the nations sugar produce is lost to disease caused by Fungi, bacteria, viruses, phytoplasma and nematodes. Employing agronomical methods like using disease free setts, the burning of trash, crop rotation, use of healthy seed, adequate drainage in fields, avoiding ratooning of diseased crop, clean cultivation and destruction of all plant debris, use of resistant varieties, regulatory control, thermal and chemical treatment, rouging of diseased clumps, use of long setts, good field hygiene, collateral hosts and disinfections of seed cutters help in the control of sugar cane diseases. The major diseases of Sugar cane are the red rot, smut, wilt, sett rot, ratoon stunting, grassy shoot, mosaic, yellow leaf disease, top rot, pokkah-boeng and foliar diseases such as rust, eye spot, yellow spot, brown stripe and ring spot.
Integrated disease management would involve proper site selection and preparation, utilizing resistant cultivars, altering planting practices, crop rotation, improving drainage, adequate irrigation, pruning, rouging, thinning, shading, pretreatment of setts and application of pesticides wherever required. It also involves monitoring environmental factors (temperature moisture, soil chemistry including nutrients), disease forecasting and establishing economic thresholds.
Pests and their control
Sugar cane may be infested by about 288 insect pests of which about 2 dozen may cause heavy loss to the quality as well as yield crop. Agricultural chemicals are widely used to protect crops form pests. The major invertebrate pests on sugar cane are cane grubs, cicadas, ants, symphylans, nematodes, wire worms, adult beetles, spittle bugs and frog hoppers, weevils, shoot borers, thrips, sugar cane weevil borer, termites, locusts, army worms and loopers, plant hoppers, mealy bugs, aphids, and scale insects. Damage may be caused through boring in the cane stalk, cutting the leaf spindles (shoot borer). In some, the caterpillars may enter the stalk from the soil surface not more upward but remain in the base (root borers). Newly hatched larvae may feed on the leaf sheath by scrapping and later boring into the tender leaf top (internode borer). The top borer, one of the most serious pests, infests cane at all the stages affecting the leaves and damaging the central shoot. Adults and nymphs of some pests (pyrilla) suck the sap from the under surface of leaves and cause damage. Some like the wooly aphids may secrete a dew like substance on which a sooty black fungus develops which hinders the photosynthetic activity of the plant. White grubs may feed on the roots of sugar cane.
The plants eventually wilt and dry up due to the feeding of grubs on the roots. The canes fall down. Thrips may rasp the upper surface of the leaves and suck the oozing sap as result of which the leaf tips are rolled. The oval and flattened nymphs stick in wax over the nodal region.
Integrated management of pests includes use of resistant varieties, inter cropping, trash mulching, early planting, reducing soil temperatures, removal of dead hearts, bio control through predators, the judicious use of chemicals and pesticides, selecting pest free setts setting pheromone traps, collecting and destroying insects, flood irrigation, destroying termite colonies, fumigating termite mounds, deep ploughing, avoiding excessive use of fertilizers, appropriate seed treatment, draining excess water from field, avoiding repeated ratoons and use of bio insecticides.
A stage wise integrated pests’ disease and weed management system has been suggested which involves the integrated use of all available methods and strategies to manage the pest populations below the economic injury level (EIL) with least environmental disturbance and greatest socio-economic acceptance. Most of the procedures mentioned above are adopted. The integrated management strategy involves the efficient management of nutrients, weeds, diseases and pests through chemicals, biological and agronomic control during the pre-sowing, sowing, tillering, cane formation, reproductive maturity and post harvest stages of sugar cane cultivation.
Hybrids Cultivars and their Management.
Works on the improvement of Sugar cane varieties was started in India in 1912 with the setting up of the Cane Processing Station Coimbatore. The first successful variety was released in 1918. Breeding suitable varieties for tropical India started in 1926. In Uttar Pradesh breeding cane commenced with the establishment of the Sugar cane Research Station in Shahjahanpur during 1912. More than 212 varieties have been added since 2012 and include short duration varieties, drought tolerant varieties and varieties tolerant to salinity, cold, frost, water logging, pest and diseases. In addition varieties suitable for Jaggery and for cogeneration have also been developed.
Genetically Modified Cane
Sugarcane has a highly complex genome and is vegetatively propagated with little scope for crop improvement through conventional breeding. However, experimental work to improve cane varieties through genetic engineering has involved traits like herbicide resistance, resistance to pests and pathogens, reduction in browning of sugar cane juice, improved nitrogen efficiency, altered sucrose accumulation, inhibition of flowering and improved cellulose ethanol production. Sugar cane has also been genetically engineered for the production of altered sugars and other industrially important and human pharmaceutical product. The commercialization of genetically engineered sugar cane is very limited. Globally only four G.E. sugar cane varieties are approved for commercial purposes. One of these which has been developed for drought resistance was approved in Indonesia for food use and cultivation. There are another 03 commercially approved sugar cane varieties in Brazil, all of which are insect resistant. G.M. crops have been controversial in India.