عنوان مقاله [English]
Introduction: Qazvin plain is one of the most important agricultural regions in the central part of Iran. Because of recent continuous droughts and the increases in the demands of different sectors such as agriculture, industry, environment and domestic, the plain is faced witha severe shortage of water resources. Due to the declining share of surface waters, farmers increased the using of groundwater. And the overusing of groundwater for irrigation has caused the severe drop in water level of the aquifer. The critical situations in the Qazvin plain have made the agricultural water management and crop pattern modification vital and necessary.Due to the population increase, concepts and theories such as food security, environmental protection and sustainable management of groundwater and surface water resources, virtual water footprint and virtual water trading are a dynamic concept for water resource management in all sectors that has considered more in recent years.
Materials and Methods: The green (effective precipitation), blue (net irrigation requirement), gray (for diluting chemical fertilizers) and white (irrigation water losses) water footprints (WF) of main crop production were estimated for Qazvin plain. The average yield and fertilizer application in irrigated and rainfed lands, for main crops wasobtained from Agricultural-Jihad Bureau of Qazvin Province in for 2003-2014. Pe values were calculated by USDA method and ETc was calculated by FAO-Penman-Montieth method using the model CROPWAT. Values of α under irrigation and rain-fed were considered 5 and 10%, respectively. In this study, WFGray has been calculated just for nitrogen fertilizers. The maximum nitrogen concentration in the receiving waters based on the US-EPA Standard is 10 mg/lit. Due to the differences in crop yield under rainfed and irrigation conditions, the WF components were calculated using crop yield for different conditions, separately.
Results and Discussion: Canola and maize with 4066 and 185 m3/ton have maximum and minimum WF in the irrigated lands, due to the yield of two crops. Canola and maize have maximum and minimum yield between the irrigated crops, respectively. The total wheat WF of was estimated 2673 m3/ton in the area. The total WF in the rainfed lands is much more than the total WF in irrigated lands that is due to the significant yield differences in the irrigated and rainfed lands, especially for wheat and barley. In recent years, because of the decrease in precipitation, the rainfed crop yields have decreased considerably. Between the irrigated crops, wheat, barley, tomato, and canola are the four crops which have similar white WF (about 50%) and gray WF (about 10%). Also there are the same shares between white and gray WFs of corn and maize. The shares of white and gray WF in corn and maize are 28 and 18, respectively. These results show that agricultural practices and managements are similar. In other words, the irrigation system efficiency and fertilizer application are similar in farms and for crops. Also there aren’t significant differences in the green and blue WFs of corn and maize. These similarities in WF components are the result of approximate equalities in the evapotranspiration, effective rainfall, fertilizer application, and depth of irrigation. In irrigated lands, white WF contains about 46% of the total water footprint in the production of main crops. In irrigated and rainfed lands, about 42% of the WF is related to white water. Thus, irrigation losses are about 864 MCM/year in the region, which is really considerable for a region that faced with water shortage crisis. In rainfed lands, the gray WF component is about 13. In total. If this gray WF which is the environmental need for protecting water quality doesn’t meet, contamination of surface and groundwater resources will be occurred. Wheat has the most consumed and exported virtual water volume with 652 and 343 MCM/year, respectively. The export of wheat includes 28.4% of the total exported virtual water volume and 20.2% of the exported water resources volume. Total consumed and exported virtual water volume from the region are 1031 and 1022 MCM/year. The exported volume of blue, gray and white WFs consists about 783 MCM/year. Therefore, considerable volumes of groundwater and surface water resources exported from the region by exporting main crops. The exported weight of maize, corn, alfalfa and tomato from the region is greater than the weight of consumption in the region. The total of blue, gray and white WFs is much higher than the green WF of these crops. The export of these crops imports the most pressure on groundwater and surface water resources of the region.
Conclusions: Qazvin Plain as one of the most important plains in the central part of Iran faces to water shortage crisis. The concept of virtual water and WF of agricultural production help to better agricultural water management in the region. The total share of gray and white WFs in the region is about 907.5 MCM/year and 44% of the total WF in the agricultural main crop production. Low efficiency of irrigation systems and excessive use of nitrogen fertilizers in farms are the most important causes of high shares of these two WF components. The planting and export of summer crops hasa considerable share of VW trade in the region. Due to the high water requirements, the total share of blue, gray and white WFs is high in these crops. These WF components are supplied from the limited surface and groundwater resources of the region. Also, WF in rainfed crops is much greater than the irrigated crops. Droughts and rain reduction are the main reasons of severe decreasing in the yield of rainfed lands. Supplementary irrigation is a management for reducing WF and improving yield in rainfed land. VW trade volume is about 1,022 MCM/year.