Sugarcane is cultivated in India under widely varying conditions of soil types, rainfall pattern, temperature regimes and water availability. Water requirement of sugarcane varies from 1200 to 3500 mm depending on the yield level, crop duration and the climatic conditions. The water requirement varies from 1200 – 1800 mm in the subtropical zone while it is 1600 – 2700 mm in tropical belt except for Maharashtra. The total crop water requirement is about 3500 mm for adsali cane in Maharashtra (Srivastava et al., 2007).
Yates and Taylor (1988) in their comprehensive review gave WUE values ranging from 0.7 to 1.45 tonnes of cane/ha/cm in different sugarcane growing regions of the world. In the tropical region, 30 to 40 irrigations are given. In the subtropical region, there is places wherein sugarcane is grown under rainfed conditions; there are places where only 3 to 5 protective irrigations are given during summer months and there are places wherein about 15 irrigations are given. In some places, the crop suffers water logging for some period necessitating the provision of drainage facilities and moisture deficit in some other period which warrants irrigation.
Efficient water management
Irrigation is the artificial application of water to the root zone of the crop which is a supplementary to rainfall, so as to provide optimum soil moisture condition in the root zone of the crop to realize its normal growth and yield. Hunsigi (1993) reported that under furrow irrigation nearly 90% of soil moisture extraction takes place in the first 60 cm of the soil layer. However, the distribution of roots in the soil is strongly dependent on soil characteristics, cultivars and soil water content (Jones et al., 1990). In most places, rainfall is not uniformly distributed throughout the growing season of the crops. In such a situation, the crops will have to suffer water deficit at some stage or other. The objective of irrigation is to alleviate water deficit in crops at times of insufficient rainfall.
The availability of water at the farm level is not uniform throughout the year. First, an estimate of the water availability during different months of the year has to be made, the period of least water availability should be identified and the area that could be commanded with that water should be estimated. The area of a crop like sugarcane in a farm should be limited to that area. In the rest of the area, other crops of shorter duration could be grown in periods of favourable water supply. In periods of less water availability, a part of the land in the farm should be kept fallow.
When to irrigate?
Irrigation is given to supply adequate water to the plants so as to obtain optimum yield and quality. It should be given at the optimum time so that the soil could supply water fast enough to meet the local atmospheric demands without placing the plants under any stress that would reduce yield or quality. Sugarcane performs well when the soil moisture is in the upper range, very close to the field capacity. It has been found that for Sugarcane irrigation is to be given at 50% depletion of available soil moisture during the vegetative phase (from planting to 270 days after planting [DAP]) and at 75% depletion of available soil moisture during the maturity phase (from 270 DAP to harvest).
The time of irrigation is decided based on physiological indications of the plant, soil moisture status or climatological data. Verma (2004) recommended that Sugarcane crop during its formative phase should be irrigated once in 10 – 15 days in Punjab; once in 10 – 12 days in Haryana; once in 7 – 15 days in Rajasthan; once in 15 – 20 days in UP and Bihar; once in 15 days in West Bengal and Assam; and once in 10 days in MP. During the maturity phase, the irrigation interval should be once in 25 – 30 days in Punjab and Haryana, once in 30 days in UP, Bihar, West Bengal and Assam, and once in 15 days in MP.
Irrigation based on physiological indications of the plant
Plant growth is related to the water balance in plant tissues. As soon as the water supply to the plant gets reduced, the physiological processes of the plant are disturbed and growth and yield are subsequently reduced. The physiological and morphological indications of water deficiency in plants which could be used as a guide for deciding the time of irrigations are listed below.
- Appearance of the plant
- Indicator plant method (sunflower, Datura, maize)
- Plant population or density method
- Measuring the stomatal aperture
- Plant water content (crop logging)
- Leaf water potential
Irrigation based on soil moisture status
Depending on the ability of crop plants to extract water from the soil, the soil moisture status could be used to decide the time of irrigation. For sugarcane, it is necessary to maintain the moisture content of the root zone soil close to field capacity during the vegetative phase. In other words, the crop has to be irrigated before the depletion of 50 % of the available soil moisture. The methods available to assess the soil moisture are as follows
- Feel and appearance method
- Gravimetric method
- Electrical resistance units
- Tensiometers or irrometers
- Neutron scattering
- Time Domain Reflectometry
- Sugarcane Breeding Institute