Crop yield response to water - Cra

Irrigation practiceSunflower is grown without irrigation in many areas around the world. In subhumid andsemiarid regions with limited precipitation, however, irrigation is practised. The ideal scheduleunder full irrigation must ensure the quick development of a canopy, avoid water deficitsat anthesis, and maintain a green canopy throughout the seed-filling period all the way tomaturity, thus fully exploiting the genetic potential of the cultivar. This would be achievedby refilling the root zone before damaging water deficits develop at any stage. However, theirrigation schedule should take into account the capacity of this crop to extract subsoil waterby conserving irrigation water near the end of the season. Furrow and sprinkler are the mostcommon water application methods for sunflower.Deficit irrigation is frequently practised. In areas having winter rainfall, the best strategyis to develop the canopy based on stored soil water at planting and concentrate irrigationapplications during flowering and seed filling. During these two periods, the ideal scheduleshould avoid stomatal closure and the hastening of canopy senescence, while the root zoneshould be fully depleted of soil water at maturity. In situations where water resources arevery limited, the best choice for deficit irrigation is to concentrate the irrigation water aroundflowering and early seed filling. It has been shown that when vegetative growth is manipulatedby delayed irrigation, which conserves water for the flowering and seed-filling period, theharvest index can be increased relative to full irrigation regimes.YieldSunflower yields vary between less than 0.5 tonne/ha in rainfed production on shallow soilsor in low rainfall areas to over 5 tonne/ha under ample water and nitrogen supply. Typically,rainfed production between 1.5 to 2.0 tonne/ha is achieved in semiarid areas, reaching3-3.5 tonne/ha in subhumid areas of good soils. When short season cultivars are grown asa double crop under irrigation, yields of around 3 tonne/ha are obtained. Maximum yieldsof a single crop under irrigation are around 5-5.5 tonne/ha. Sunflower seeds contain a veryhigh percentage of oil (around 50 percent) and between 15 and 17 percent of protein.Consequently, the harvest index of sunflower (computed on a dry matter basis) is relativelylow, from less than 0.3 in long-season cultivars up to 0.4 in short-season hybrids. Sunfloweroil is accepted as high quality oil and is in high demand, not only for human consumption,but also for the chemical and cosmetic industries. The oil contains two main unsaturatedfatty acids (oleic acid and linoleic acid) and saturated fatty acids (palmitic and stearic). Highquality of sunflower oil is associated with higher oleic acid content. Oil concentration isincreased when adequate irrigation is provided, especially in the grain-filling stage. However,irrigation does not increase significantly the amount of oleic and linoleic acids. Direct effectsof water deficits on oil content of the seed are less than those on seed yield.sunflower 169