Investigating precipitation role on water supply, yield and moisture stress of rainfed wheat and lentil in Zanjan plain

Rainfed cultivation is one of the best ways to rich the sustainable development with optimal use of green water. About 75 percent of the world's cultivated areas are rainfed, which forms important part of the international economy. For a long time rainfed cultivation has been a common method in low-rainfall areas of Iran and mentioned method is one of the main ways of producing crops yet. Rainfall is an important factor in rainfed agriculture, so its limitations and non- conformity with planting season can reduce the production efficiency. Wheat growing period consists of three seasons of the year and rainfall in spring, fall and winter is effective on wheat growth. Cereal grains, especially wheat, are the most important food source in the world. After cereals, legumes are considered to be the main human food source and have significant nutritional and agricultural importance. In addition to being high in quality and valuable, suitable and complementary protein for cereals in the nutritional pattern, lentils are also among the legumes that stabilize the air nitrogen in the soil, which lends itself to crop rotation. Thus, intermittent cultivation of rainfed wheat with rainfed lentil is an important factor in stabilizing production in the developing countries. Given that Iran is in the arid and semi-arid regions and its population is growing, it is important to plan and evaluate the past in order to predict the future. Zanjan province is the fifth country with 6.9% of total grains production. In this study the effect of precipitation in water requirement of these two important products and their water stress in the climatic conditions of Zanjan plain has been studied.

Zanjan province is located at 47 degrees 10minutes to 50degrees 5minutes east longitude, 35degrees 25minutes 37degrees 10minutes north latitude, with areas of about 39369 square kilometers. According to the De Marten climate classification, the tropical, temperate and subtropical climatic zones can be identified at the applied level. Average rainfall over the past decade has been reported at 301 mm. For conducting this study, statistical data including meteorological and crop yield data 2004-2014 obtained from the Meteorological and Agriculture-Jahad Organization, respectively. Zanjan synoptic station with latitude and longitude 48degree 31minute east and 36degree 39minute north, 1663 meter above sea level. In the last 50year, the annual precipitation trend has been decreasing and this trend is affecting the water availability of rainfed plants in the region and can decrease yield of crops. Although in the long term, the average temperature trend is somewhat constant, but with decreasing rainfall, the yield has also decreased. in this study, due to the importance of wheat and lentil as two main crops of rainfed and their placement in arid lands of Zanjan plain, investigated the regression relationship between yield and evapotranspiration with precipitation and water stress coefficient.

The results showed that the average evapotranspiration values of wheat and lentil for Zanjan plain during the study period were 398 and 262 mm and the mean temporal stress coefficients were 36 and 33%, respectively. Regression analysis showed the highest correlation between actual evapotranspiration and yield so, the highest correlation between temporal stress coefficient and yield of rainfed wheat. But in lentils this trend was different and the correlation between water stress coefficient (Ks) and yield is more than the precipitation and lentil yield. For 25% decrease in precipitation, wheat yield reduced almost 18%. Generalizing this issue, the response to water stress coefficient of the product or Ky become 1.14. The regression equation also showed that in case of being precipitation about 300 mm, wheat yield in the area will be near one tone. For 25% decrease in precipitation, wheat yield reduced about 22%. According to figures, the fitted model was significant and well acted; and during the growth period of these crops, lack of water supply caused water stress as well as severe yield loss. The occurrence of high tension time percentage of 25% for wheat and 20% for lentil in all years of study period confirms the climatic potential of the region does not rich the standard requirements of plants and it is not possible to achieve optimal performance, so new methods of tillage, conservation agriculture and supplemental irrigation are recommended for achieving high yield, as well as the expected cultivation method for crops.