Influence of Topography and Latitude on Rain Water Productivity and Rainfed Barley yield

Low cereal and legumes yields and their RWP index are mainly due to poor distribution of rainfall and poor agronomic management practices. Rainfed barley yield and rain water productivity (RWP، defined as rainfed grain yield divided by the total crop season annual rainfall water) in the dry farming are considerable by topography and latitude. Yield data، rainfall، altitude and latitude of 182 points during the 2003-2007 were used. Total rainfed barley areas under consideration are 1. 032 million ha، total rain water available at this area is 4. 726 billion cubic meters and barley yield was obtained equal to 1019 kg/ha. Average rain water productivity of rainfed barley was obtained 0. 239 kg per cubic meter. Areas of study، 32. 4% areas have less than 85 percent of the average rain water productivity، 26. 4 % have between 85 and 115 percent of of the average rain water productivity and 41. 2% have more than 15 percent of the average rain water productivity. While، the rain water productivity of 80% areas less than 0. 33 kg per cubic meter، only yield of 20 % area are more than 1303 kg/ha. Yield of 60% area (with RWP less than 0. 28 kg. m-3) is less than 1027 kg/ha. Rain water productivity on the rise from latitude 32 and this trend continues until latitude 37. 5. Relationship between topography and barley yield is a negative linear and highest frequency is topography ranges from 1200 to 1800 m. With increasing topography، RWP increased، and highest frequency is topography ranges from 1000 to 1800m and then gradually decreased rain water productivity.