In this article we will discuss about the effect of irrigation at different stages of crop growth on the yield of sugarcane.
For limited water supply situations, irrigation should be given at relatively more sensitive stage of crop growth of sugarcane. At IISR, Lucknow, entire summer period of crop was divided into four phases germination, first, second and third orders of tillering and irrigation either was given or missed at any one or two of these stages (Table 18.16).
Water use efficiency (WUE) under field conditions is low ranging from 0.4 to 0.6 t ha-1 cm-1. Ideally, WUE of 1.0 t cane ha-1 cm-1 of water is desirable which can be achieved by adoption of appropriate water management practices.
The results indicated that when water is available for only one irrigation, it should be given at third orders of tillering. With the availability for two irrigations, second and third order of tillering are the most responsive stages.
Three irrigations when given at first, second and third orders of tillering resulted in almost the same yield as was with four irrigations. In other words, tillering, grand period of growth and early ripening stages are most critical for irrigation.
Scheduling Irrigation:
Several approaches are used for scheduling irrigation to sugarcane out of which schedules based on available soil moisture (ASM) and IW/CPE ratio are relatively more common than other methods.
Irrigating February planted cane crop at 75 per cent ASM requires 10 irrigations as against 6 irrigations at the same soil moisture regime for April planted crop. Even at 50 per cent ASM, February planted crop required 7 irrigations as against only 3 for April planted crop (Table 18.17).
Irrigation at 80 per cent sheath moisture content produced highest yield at Sehore and Caddalore. At Pusa, however, irrigation at 0.7 IW/CPE ratio or 50 per cent ASM produced significantly higher can yield. Use of trash mulch reduces the water requirement leading to high WUE.
Based on the results of experiments, the following water management practices can be recommended for sugarcane:
1. Pre-monsoon is the crucial period in tropical and subtropical regions for irrigation.
2. During rainy season, sugarcane crop needs 6-12 irrigations in tropical regions, while irrigation is not necessary during monsoon in subtropical region, except when rains are scanty and erratic.
3. In the post-monsoon, 1-2 irrigations are needed in subtropical region as against 6-14 in the tropical region.
4. During the post-monsoon, relatively low moisture content (around 25% ASM) should be maintained to facilitate ripening and increase sucrose content.
5. In general, scheduling irrigation at 50 per cent ASM or 0.7 IW/CPE ratio is ideal for sugarcane.
6. Tillering, grand growth period and early ripening period are more sensitive to soil moisture stress.
7. Generally, a drying off period of 4-6 weeks prior to harvest has to be allowed.
8. Flooding or high water table during monsoon should be avoided by providing adequate drainage.
Water deficit during the grand growth period results in reduced rate of stalk elongation. Severe deficit in the latter stages forces the crop to ripen faster. A low soil moisture (25% ASM) is required during ripening period. Water requirement of sugarcane is high in tropical region ranging from 2000 to 3000 mm against 1500-2000 mm in subtropical region.
Methods of Irrigation:
Furrow method is the most commonly used method. Skip-row method is ideal under limited water situations. In this method, instead of irrigating all the rows and inter-row space, one row is skipped for irrigation purpose and irrigation is given in alternate rows.
In this method, sugarcane is planted in flat beds and after germination, 45 cm wide and 15 cm deep furrows are made is alternate inter-row spaces. At the time of irrigation, the furrows made thus are filled with water. This method saves about 35 per cent of irrigation water and increases the water use efficiency by around 64 per cent.
In the modern drip irrigation, soil moisture is maintained at or near field capacity closer to roots. Drip irrigation has been adopted on a large scale in Maharashtra. The Vasantdada Sugar Institute, Pune reported that surface and subsurface drp with daily irrigation and paired row planting saved 45 to 50 per cent of water, 2 to 2.5 increase in WUE, 20 to 30 per cent yield increase and 0.2 to 0.6 units increase in sugar recovery.
High cost of installation and maintenance limit its adoption by marginal sugarcane growers.