1. Receding water levels in Ogallala aquifer are threatening the sustainability of irrigated agriculture in the High Plains of Eastern New Mexico and West Texas. Alternate water management strategies are needed to prolong the aquifer water availability for agriculture. The value of stressing plants slightly to induce water conservation mechanisms has been documented. The aim is to reduce luxury consumption of water, which is not contributing too much to the yield formation. Stressing part of the root system of the plant, alternately during each irrigation, has received attention recently. In this method, the wet side of the root system maintains plant productivity and dry side of the root system triggers water conservation strategies. Switching wet and dry side at each irrigation is expected to further improve crop performance. Sunflower is well adopted to the region with better heat and water stress tolerance. The deep root system of sunflower can acquire water from depth to sustain the crop productivity between irrigation intervals. The response of sunflower to stressing part of the root system alternately is not known. Water Stress on Alternate Side of Root System to Improve Water Use Efficiency of Sunflower Sangu Angadi *1, Wahby Ahmed 2, Sultan Begna *1, and Calvin Trostle 3 * Dept of Plant and Environmental Sciences & 1 Agriculture Science Centers at Clovis, New Mexico State University, Clovis, NM 88101, 2 Desert Research Center, Cairo, Egypt 3 Texas AgriLife Extension, Lubbock, TX 79403 RESULTS INTRODUCTION For more information: Sangu Angadi: angadis@nmsu.edu Ph: 575-985-2292 Ex105 MATERIALS AND METHODS Location: Clovis, NM Year:2008 and 2009 (summer) Hybrids:Tall: Triumph 859HOCL Dwarf:Triumph s672 Planting:May 5 th (both years) Seasonal rainfall:≈ 200 mm Irrigation method:Surface drip system with water meters SUMMARY Acknowledgement: We thank the National Sunflower Association and the New Mexico State University, Agricultural Experiment Station for the financial support. Technical help from Aaron Scott, Joleen Szaloy, Miguel Nunez, Cecily Strait, Jessie Reyna and Maria Nunez is greatly appreciated. Study the growth, physiology and yield responses of sunflower to water stress imposed on alternate sides of the root system with each irrigation. Test sunflower stress responses at high and low irrigation levels. Compare the response of tall and dwarf sunflower hybrids with different growth architecture to alternating partial root stress. Figure 5. Effect of alternate irrigation methods and amounts on plant height, harvest index, seed yield and oil content of dwarf (left bar) and tall (right bar) sunflower hybrids in 2008 at Clovis, NM. Leaf Area Index Days after seeding (d) OBJECTIVES Results are preliminary and the second year samples are being processed. Soil moisture content was measured during the growing season using a neutron probe. The data is being assessed to see the effect of irrigation amounts and methods on water use efficiency. Irrigation amounts significantly affected leaf area index of both sunflower hybrids. Sunflower receiving 300mm irrigation water had higher leaf area index compared to 150mm treatments (Fig. 3). Alternatively stressing part of the root system did not show any consistent effect on leaf area development. Sunflower leaves were damaged by hail storm at 65 days after planting in 2008. Sunflower crop recovered but, leaf area index was reduced. Occasionally photosynthesis and stomatal conductance observations indicated that alternate irrigation strategy conserved moisture for higher photosynthesis later in the dry cycle (Fig. 4). However, it was rarely reflected in yield. Photosynthesis response of sunflower to light intensity indicated that difference between irrigation treatments was more pronounced when the sunlight was at peak or at productive part of the day. In spite of large architectural differences between two hybrids, their plant height responded similarly to both irrigation methods and amounts (Fig. 5). Plants were taller in higher irrigation treatments. Irrigation method had no effect. Harvest index was not affected by irrigation amounts, methods and hybrids. This suggests that alternate irrigation method did not favor reproductive growth at the cost of vegetative growth. Seed yield of tall sunflower hybrid was higher than that of dwarf hybrid. Seed yield of both cultivars increased with the doubling of irrigation amounts. Alternate irrigation methods did not have consistent effect on seed yield. Oil content was higher in dwarf hybrid than in tall hybrid. Higher irrigation amounts increased seed oil content. Alternate irrigation method had no effect on oil content. Mid-season rainfall might have affected the sunflower response to alternatively stressing part of the root system. Under the frequent irrigation situation of this trial, we did not observe great benefit with alternately stressing part of the root system of sunflower. Further research is needed with other crops. Figure 1. Regular and alternate row irrigation of sunflower at Clovis in 2008. In regular irrigation, both sides of sunflower row is watered during each irrigation. In alternate row irrigation, only one side of the sunflower row gets all the water intended for both sides and irrigated sides are switched with each irrigation. Regular Alternate This IrrigationNext Irrigation 859HOCL (Tall) s672 (Dwarf) Figure 2. Tall and dwarf hybrids used for the study showing the architectural differences at flowering in 2009 at Clovis, NM. Figure 3. Seasonal pattern of leaf area index of dwarf and tall sunflower hybrids in response to irrigation management in 2008 and 2009 at Clovis. Arrow in 2008 indicates hail storm that damaged sunflower leaves and affected seasonal pattern of leaf area index. Pn (μmol m -2 s -1 ) Cond (mol m -2 s -1 ) Light levels (μmol m -2 s -1 ) Figure 4. Photosynthesis and stomatal conductance of tall sunflower hybrid in response to irrigation and light levels at Clovis in 2008. The observations on the left (a) were recorded next day after irrigation, while the observations on the right (b) were recorded 5 days after irrigation (a day before the next irrigation). Tall 2008 Dwarf 2008 Tall 2009 Dwarf 2009 (a) (b) 150mm 150mm (Alt)300mm (Alt) 300mm 150mm 150mm (Alt)300mm (Alt) 300mm Plant Height (cm) s672 859 Seed Yield (kg ha -1 ) Oil Content (%) Harvest Index