Introduction

• Extremely high yields can be obtained from irrigated sunflowers, and provided suitable varieties and watering techniques are used, the crop can be very profitable.
• However, there are almost unlimited combinations of climate and environmental factors affecting irrigated sunflower, and optimum yield, or more importantly in many areas optimum water use, can only be determined locally.
• Control of watering schedules is equally important, and some system of accurately determining water need or soil moisture level is essential.
• Sunflower do not wilt under moisture stress as quickly or as obviously as many other irrigated crops, and visual assessment of water need is unreliable.
• Another factor of importance in achieving maximum yield is the time of planting, which can differ significantly between rain-grown sunflower is sown in late December but irrigated crops are sown in May.
• The height of plants in relation to a relatively restricted root system, when grown under irrigation in areas where high winds are common (and this combination occurs in many countries suitable for sunflower), plants are easily uprooted for wet soils gives little support.
• Since the last watering is usually applied as the heads are maturing to ensure the seeds are filled, plants are exposed to maximum leverage on the roots when most vulnerable.
• Lodging losses at this period can be very heavy even in small holder crops, since the heads fall on to wet soil and may rot before they are collected.
• Short varieties should be used whenever possible, even if seed-oil content may be lower than taller local varieties.
• There are also indications that seed-oil content and protein content of some hybrids may be higher when grown under irrigation than when rain-grown.
• During vegetative growth period this crop can tolerate drought but flowering is very critical stage for irrigation.
• Stop irrigation at 80 days age crop, otherwise lodging will be seen.

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Method of irrigation

Furrow irrigation system is ideal for sunflower as this system is the simplest system and also highly efficient especially under undulated land. Depending upon soils and season, apply irrigation water at intervals of 20-25 days in case of black soils and 8-10 days in case of red soils .

No.of irrigations Vs Type of soils

• Avoid excessive and too frequent irrigations since such a practice pre-disposes the crop to attack of wilt and root rots.
• Whenever water is a constraint, provide irrigation at the three critical crop growth stages mentioned below for realising maximum response from the scarce input, water.
• Avoid moisture stress at more sensitive crop growth stages, as it will have serious effect on seed set, filling and consequently on the yields.

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Scheduling irrigation

• Soil deficient in moisture , requires one pre-soaking irrigation for the good germination of seed .
• Thereafter ,irrigation must be given according to the need of the crop.
• If there is sufficient timely rain in Kharif season , no irrigation is needed .
• Two to three irrigations are needed for a good crop of rabi season and the summer crop should be irrigated at an interval of 15 to20 days.
• Twenty days before flowering and Twenty days after flowering is the critical period for water requirement.

Critical crop growth stages

• The most critical periods for irrigation in sunflower are bud (button) stage, flowering and grain formation stages.
• If the crop experience moisture stress at these stages the no. of ill filled grain flower will be increased.
• Under limited water conditions provide irrigations at bud stage and grain formation stage.
• If there is water sufficient for only are irrigation, irrigation should be scheduled only at flowering.

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Water utilisation and its effects

• When following a heavily watered crop, or where there is naturally high sub soil moisture, sunflower will produce good yields with only 300-500mm of added water.
• In normal conditions, water use by sunflower is mainly confined to the upper 150 cm of the soil, but root penetration to at least twice this depth is frequently recorded.
• When fully surface-irrigated, 600-750mm is considered the minimum, to include any rainfall.
• It has been shown that water use by sunflower is twice that of sorghum at any given leaf area.
• A watering prior to sowing and one as the heads are forming are essential, with at least two other applications at appropriate intervals between.
• Experimental work has shown that water stress at anthesis resulted in a greater reduction in seed yield than stress in later stages of development.
• Not only is there an overall reduction in seed yield, but the oil content and kernel percentage can be reduced.
• The most obvious field symptom is an increase in the number of unfilled or aborted seeds in the centre of the plant heads, although inadequate pollination or soil nitrogen may also be partially responsible.
• Irrigation later than 21 days after mid-flowering has little effect on the yield, and can cause harvesting problems by keeping the surface too wet to allow use of harvesting equipment.
• Although many tall varieties of sunflower are considered drought resistant, the potential yield of newer cultivars is quickly reduced by a water stress.
• Chemicals can also reduce the effects of moisture stress. Chlormequat for instance, when applied to plants in the ten-leaf stage, significantly reduced water use in the following 21 days.
• It is important to keep to an irrigation routine of stated intervals rather than watering when plants show stress as is common practice with other crops.
• Sunflower's large, substantial leaves do not always quickly wilt, and it is unwise to use visual symptoms as a guide.
• Excess moisture is detrimental to sunflower at any growth stage, and the degree of damage is directly related to the duration of water-logging.
• Very short periods,2-3 days, affect young plants more severely than those older, and several such periods are less damaging than a single period of 3-7 days.
• Saline water is generally unsuitable for irrigating sunflower, although there are varietal differences in response to salinity.
• Where it must be used, moderately saline water can be expected to reduce seed-oil content by up to 50 per cent.
• Salinity also tends to increase the severity and incidence of root rots.

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