Abstract
The Amu Darya River is the major water source for Turkmenistan contributing 88 % to the total amount of surface water available to the country. Lebap Province harbours oases and natural riparian vegetation along the Amu Darya River. In the oases, cotton, wheat, and corn as well as fruit and vegetables are grown under irrigation. While cotton was strongly promoted during Soviet Union times, the wheat area was enlarged after independency of Turkmenistan, in order to secure food self-sufficiency. In the literature, a very high crop water requirement has been reported for cotton in Turkmenistan. In this paper, the objective is to investigate the consumptive water use, i.e. actual evapotranspiration, of the major crops cotton, wheat, and corn, the household plots, and the natural vegetation within Lebap Province of Turkmenistan. Actual evapotranspiration (ETa) was mapped from Landsat satellite images for the vegetation seasons 2009 and 2010. Additionally, reference ET (ETo) and crop ET (ETc) were calculated. ETa for riparian (Tugai) forests and Tamarixshrubs was 907–1,043 and 239–259 mm, respectively. ETa for the mapped crops cotton, wheat, rice, and gardens was 485–658, 156–350, 685–935, and 416–615 mm, respectively. ETo was 929 and 979 mm in 2009 and 2010, respectively. ETc for cotton and rice was 896 mm in 2009 and 925 mm in 2010 and 1,085 mm in 2009 and 1,198 mm in 2010, respectively. The low ETa values are explained partly by under-estimation through the method applied, partly by low yields of the crops. There is a big gap between the amount of water taken up from the Amu Darya and the water really consumed by the irrigated crops. This low water use efficiency might be due to water losses from channels and high amounts of water needed for soil preparation, i.e. leaching of salts.