A Determination of Water Productivity Indices under Sowing Date and Single Irrigation Management for Two Rainfed Barley Varieties

The main objective in production of any rainfed crop, including barley farming is to increase water productivity along with stability in the production of the rainfed crop through improvement of the agronomic management including limited Single Irrigation (SI) and Sowing Date (SD). In order to determine optimal SI management and limited water allocation scenarios, a field experiment was conducted as split-split plot (Randomized Complete Block Design, RCBD) of three replications during two crop seasons, 2004-2006 for two advanced rainfed barley varieties at the main station of Dryland Agricultural Research Institute (DARI) in Maragheh county. The treatments included three SD, five SI scenarios and two rainfed barley varieties (V1=Abidar, V2=Dayton). Amounts and ranges of Rain Water Productivity (RWP), irrigation water productivity (IWP), and total water productivity (TWP) in producing grain, straw and biomass yields, were used to determine optimal program of single irrigation scenarios. Early sowing date for rainfed barley and heavy spring irrigation (100% depletion of available water at root zone) exerted no significant effect on rain water productivity. Early heavy irrigation (100 mm) increased straw. The results revealed that, 100mm-SI at planting time, total water productivity increased up to 8.7 and 8.9 kg.mm-1 for V1 and V2, respectively and also irrigation water productivity increased by 37.4 and 38.5 kg.mm-1 for V1 and V2, respectively. One time limited spring irrigation (50% depletion of available water at root zone) in spring and during the heading to flowering stage, exerted significant effects on yield and increased TWP to 5.6 and 5.8 kg.mm-1 for V1 and V2, respectively. It also increased IWP up to 58.9 and 60.5 kg.mm-1 for V1 and V2, respectively. A comparison of the two rainfed barley varieties, showed that, rain water productivity of Dayton cultivar was equal to 3.2 kg.mm-1, 10 percent more than that of Abidar rain water productivity.