Improving Rain Water Productivity (RWP) by Supplemental Irrigation and Agronomic Management Practices at Rainfed Areas of Upper Karkheh River Basin (KRB), Iran.

The Karkheh River Basin (KRB) is located in the south-western parts of Iran. Most of the agricultural area in the upper KRB is rainfed and a large part of the region's agricultural livelihood is based on dryland farming systems. Current water productivity (WP) values for dryland crops range from 0.3 to 0.5 kg m-3. This is in spite of the fact that the upper catchments in the KRB are among the most suitable rainfed zones of the country, with long-term annual precipitation of 300 to 600 mm. Low WP is mainly due to poor distribution of rainfall and poor agronomic management practices To study the options for increasing water productivity in the basin, on-farm trials were conducted during the 2005-08 winter cropping seasons of wheat and barley at multiple farms across two benchmark watersheds of Merek (Kermanshah Province) and Honam (Lorestan Province) in the upper KRB. Under farmers practice at rainfed areas of Merek site, grain production for a local and an advanced barley variety (Sararood1), and a local and improved wheat variety (Azar2), were 1000-2100, 2100-2900, 800-2000, and 2000- 2700 kg per ha, respectively. Early planting with the help of a single supplemental irrigation (about 75-50 mm), at Merek site, increased production to 3500-3700 for barley and 1800-3100 kg per ha for wheat. Similar results were obtained at the Honam site. The value of present rain water productivity (RWP, defined as rainfed grain yield divided by the total crop season annual rainfall water) for wheat, barley, and chickpea were 0.3 to 0.5, 0.3 to 0.6, and 0.1 to 0.3 kg m-3, respectively. The results of this study showed that combination of advanced management with a single supplemental irrigation (SI) application at sowing or spring time (during heading to flowering stage) increased total water productivity (TWP, defined as grain yield divided by the sum of total crop season annual rainfall and irrigation water) of wheat and barley from a range of 0.3-0.37 kg m-3 to a range of 0.45 -0.71 kg m-3. The irrigation water productivity (IWP, defined as the ratio of increase in grain yield by supplemental irrigation to the irrigation water applied) Created with Print2PDF. To remove this line, buy a license at: http://www.software602.com/ of wheat and barley reached a range of 0.55-3.62 kg m-3 by using single irrigation at sowing or spring time. These preliminary results confirm the potential of supplemental irrigation and advanced management as an effective method to enhance productivity. Results of deficit irrigation (DI) studies showed that under DI conditions, crop water productivity for irrigated wheat in the two sites was higher than under full irrigation conditions. Deficit irrigation not only increased water productivity, but also farmers' profits. Under pressurized irrigation, total water productivity achieved under a 25 percent water deficit was 1.2 times that achieved under normal irrigation. Besides, a soil water and salt balance model (BUDGET) and a crop water productivity model (AquaCrop) were used to simulate grain and biomass yields, soil moisture content and evapotranspiration of winter wheat sown early with single irrigation scenarios. Experimental data from three growing seasons (2005–2008) were used. The experimental design incorporates Azar2 bread wheat cultivar tested under three treatments: no irrigation at sowing (rainfed), supplemental irrigation at sowing with 75 mm of water (SI sowing) and irrigation to replenish the total water requirement at 0–90 cm soil profile at spring (about 50 mm of water). Crop input parameters were selected from the model documentation and experimental data. The first crop season, field experimental data were used for model calibration and the other two crop season data were used for simulation. Results showed that BUDGET (2005) and AquaCrop (2010) were able to simulate grain yield reduction, soil moisture content (SMC) and evapotranspiration as observed in the field experiments. Finally, economical analyses of different treatments for wheat and barley at Honam site show that all treatments, except early planting with SI, were non-economical. Accordingly, at Honam, recommended management are in the following ranking: Advanced management (AM) + planting SI, AM + SI spring, and AM + rainfed treatments, respectively. Traditional management with SI or without SI is not recommended. Similar results with spring SI and early planting SI scenarios are recommended at Merek for both wheat and barley.