The abiotic stresses limiting sugarcane and sugar productivity include drought, waterlogging, soil induced stress, low temperature, high temperature, toxic ions in certain effluents etc. These stresses affect growth and cause extensive losses in cane yield and sugar production.
Factor # 1. Drought:
Drought is the single most important factor limiting sugarcane productivity. If it occurs at critical stages for soil moisture, yield reduction will be very high. Both in tropical and subtropical India, sugarcane is subjected to high atmospheric temperatures, rapid loss of moisture leading to drought either complete or partial due to inadequate irrigation facilities during formative phase.
The crop remains stunted with constricted internodes, reduced stalk population and pith formation resulting in decreased cane and sugar yield.
Drought tolerant/less water requiring varieties:
In Madhya Pradesh, Co 449, Co 617, Co 853, Co 1307 varieties require relatively less water for optimal yield. In Uttar Pradesh, CoS 767 and CoLk 8102 can thrive under limited water situation. Drought tolerant varieties are CoA 7602, CoT 8201, CoA 8402, Co 7717, Co 8145, Co 8208, Co 8362, Co 86011, Co 85007, CoC 90063, CoC 6806, CoC 85061, Co 8371, Co 87025 and Co 87268.
Efficient Use of Limited Water:
If water is available for one irrigation only in subtropical India, the crop should be irrigated when the third order tillers have emerged in June. In tropical India, it should be applied one month after the lifesaving irrigation given 12 days after planting during formative phase.
In subtropical ratoon crop, one irrigation subsequent to harvest of plant crop and one premonsoon irrigation along with fertiliser application (half of the recommended dose) appear to be ideal. Drip irrigation can substantially bring down the irrigation needs at such situations.
Trash Mulching:
During formative phase, both under tropical and subtropical India, trash mulching improves cane and sugar yields. Trash mulching soon after planting combined with urea spray on 90, 105 and 120 days after planting (50 kg N ha-1 for 3 sprays) can minimise the adverse effect of drought.
In some parts of tropical India, adsali crop, planted in June/July, is subjected to moisture stress during late grand growth and maturity. Application of potassium (60 kg K2O ha-1) and mulching in alternate furrows in February/March can improve cane and sugar yields.
Besides these, inducing drought hardiness by soaking setts in saturated lime solution for 2 hrs, trench planting, use of antitranspirants (kaolin 6% spray) during formative phase (60-150 days after planting), urea and potassium chloride spray (2.5% each) at 60, 90 and 120 days after planting and potassium sulphate (2%) spray during hot summer mitigates drought and improve the cane yield.
Factor # 2. Waterlogging:
Waterlogging is one of the major constraints in sugarcane productivity. In India, 20-30 per cent of sugarcane area is waterlogged. Waterlogging occurs due to rise in water table in almost all the canal irrigation areas.
Tolerant Varieties for Waterlogging:
Waterlogging tolerant varieties are:
CoP 1, CoP 2, Bo 91, Bo 99, Bo 43, CoSe 9530, CoSe 96436, Co 8231, Co 82323, Co 8145, Co 8371, CoSi 86071, CoSi 776, Co 62175, CoT 8201, CoT 88322, Co 87268.
Early planting enables the crop to grow sufficiently tall by the time of waterlogging (August- September). Planting rayungans or pregerminated setts is recommended for waterlogged areas.
Method of Planting:
Trench (60 cm wide, 30 cm deep at 175 cm distance) planted can appears to withstand waterlogging better due to good growth as this practice facilitate irrigation and quick drainage of water, once the flood water starts receding and improves juice quality.
Excavated loose soil kept on rides is used for filling the trenches in stages as the crop grows. At 180 days, shallow furrows remaining in the field in between two pairs of sugarcane rows serve as effective drainage channels. With such a system of planting, advantage in succeeding ratoon crop is relatively higher.
Planting on Ridges:
Waterlogged areas, which tend to get inundated with 60-120 cm deep water, ridges are manually made in February-March. These are 45-60 cm high from soil surface and 90-120 cm from bottom of the furrow in between. These furrows contain water and sugarcane crop remain much above it. This practices allows improvement in drainage and ensures aeration for roots as the root zone is above water level.
Nutrient and Soil Management:
Application of 2 per cent nitrogen under trench planting improves cane yield under waterlogging. Foliar application of 2.5 per cent urea plus 2.5 per cent potassium chloride is also beneficial. Waterlogged soils can also be managed by incorporation of organic residues, FYM, compost, press mud, green manuring etc.
Factor # 3. Soil Salinity and Alkalinity:
Soil salinity and waterlogging are the common menace in all the major irrigation projects in the country. Many perennial stream waters in low rainfall areas of Maharashtra show high sodium concentration in summer. Critical levels of salinity (level of salinity at which can yield is reduced to 50%) ranges from 6.6 to 11.0 EC (m mhos cm-1) both in subtropical and tropical India.
Tolerant Varieties:
Sugarcane varieties tolerant to salinity/alkalinity are Co 8208, Co 7717, Co 85004, Co 85007, CoC 671, Co 6806 and Co 86032. Under alkaline conditions varieties Co 87363, Co 87268, Bo 91, CoLk 8102 and Co 767 performs better.
Management of Rhizosphere Salinity:
Incorporation of bulky organic manures such as FYM 25-40 t, press mud 5-7.5 t and compost 15-20 t ha-1 and green manure (Susbania aculeate) followed by leaching out the soils is ideal for minimising rhizosphere salinity. Application of gypsum at 1.7 t ha-1 to remove one meq sodium 100-1 g soil with irrigation is also effective.
Addition of sulphur (150 kg ha-1) in combination with FYM or gypsum is useful for reclaiming alkali soils. Sodic soils can be reclaimed by application of gypsum and growing lowland rice or mulching. Application of pyrite 2 t ha-1 is also effective. Sugarcane cultivation on partly reclaimed alkaline soils can only be taken up when soil pH comes down around 9.3 (ESP 35%). Variety Co7717 performs best under such partly reclaimed soil.
Reducing Damage to the Crop:
Reducing inter-row spacing and east to west ridge direction can minimise the damage to the crop. Crop rotations involving Dhaincha – sugarcane – cotton – onion and Adsali cane – onion cotton can improve the cane productivity. Sugarcane – cotton – lowland rice -Sesbania aceuleata is ideal on partly reclaimed soil. In alkaline soils, cane yield can be doubled by planting the cane in deep (20-25 cm) furrows and packing trash in furrows as soon as germination is completed and tillering starts.
Sugarcane on saline-alkaline soils suffers from phosphorus, iron and zinc deficiency.
Suggestions to overcome the problem are:
1. Enriched compost with superphosphate at 2 kg P2O5 10-1 t and thoroughly mix it with soil before planting.
2. Apply 10 kg Fe SO4 ha-1 before planting or spray 4 kg Fe SO4 in 1000 l water, 3-4 times on the standing crop.
3. Apply 15 kg Zn SO4 ha-1 before planting or spray 4 kg Zn SO4 ha-1 (2-3 sprays) at 8-10 days interval.
4. Use ammonium sulphate as the source of nitrogen or apply 10 kg S for every 100 kg urea applied to the crop.
Factor # 4. Low Temperature:
In India, sugarcane cultivation at 30°-32°N latitude (western UP, Haryana, Punjab and northern Rajasthan) are prone to low temperature stress.
Tolerant Varieties:
Sugarcane varieties Co 842, Co 1148, CoJ 46, CoJ 83, CoJ 79, CoJ 84, CoJ 77, CoJ 81 and CoJ 76 are frost tolerant.
Improving Germination:
Transplanting activated buds by placing them in cow dung for 24 hrs ensures germination against frost in December-January.
Intercropping:
Potato + wheat or mustard in spring planted sugarcane saves the crop from frost.
Factor # 5. High Temperature:
Tillering phage of spring/autumn planted crops, early growth phase of late planted crop after wheat harvest and sugarcane to be crushed beyond mid-April are affected by high temperature stress.
Losses in flowered cane and postharvest deterioration increase with increase in ambient temperature. Canes, not harvested up to mid-April experience driage and desiccation due to high temperatures. To overcome the effects of high temperature stress, trash mulching during early growth and tillering and irrigation is desirable.
Factor # 6. Pollutants:
For the tannery effluent affected areas CoC 771 and CoC 95076 sugarcanes are ideal. Trash mulching or coir pith mulching improves cane yield under such conditions.