Multi-years required irrigation times of winter wheat and summer maize and analysis of irrigation in representative growing seasons in northern Henan

With globe climate changing, the intensifying uncertainty of precipitation induced inconsistency of irrigation schedule in different years and at different growth stages of crops. Therefore, conventional irrigation schedule fails to guide irrigation activities precisely. It becomes increasingly important for irrigation management and sustainable development of agriculture to explore changes of agricultural irrigation requirement against the background of frequently extreme meteorology events. In this paper, meteorological data of the recent 63 years (from 1951 to 2013) and soil data in Xinxiang City of northern Henan, as well as crop growth parameters were used to establish the model of drought irrigation index according to the relationships among precipitation, irrigation, evapotranspiration (ETC) and available soil water. In the model, drought irrigation index (DII) was 1, 1. Once DII was less than 0, irrigation was necessary. On the basis of winter wheat-summer maize planting schedule in the study area, the model was used to calculate multi-year DIIs for the recent 63 years. Consequently, annual irrigation times potentially meeting the agricultural requirement were obtained based on DIIs from 1951 to 2013. Three representative growing seasons of winter wheat and summer maize were selected as wet (19851986 for winter wheat, 2003 for summer maize), normal (20042005 for winter wheat, 1993 for summer maize) and dry (19831984 for winter wheat, 2009 for summer maize) growing seasons. Water requirement of two crops in different growing seasons were calculated, and DIIs in there representative growing seasons of winter wheat and summer maize were calculated too under the conditions with and without irrigation. The results showed that required annual irrigation times ranged from 2 to 7 with an average of 5.1 in recently 63 years in norther Henan Province. ETC of winter wheat and summer maize in wet, normal, dry growing seasons were 489.4 mm, 551.4 mm, 481.7 mm and 466.1 mm, 477.8 mm, 529.3 mm, respectively. Under the condition without irrigation, the winter wheat and summer maize suffered varying degrees of drought in typical growing seasons. Winter wheat respectively needed 2, 3, and 4 times irrigation, while summer maize respectively needed 1, 2 and 3 times irrigation in wet, normal and dry actual representative growing seasons. Even if in wet growth seasons of summer maize, irrigation also required during periods with high ETC but no timely rainfall. DII could guide irrigation well according to the relationship among meteorology, available soil water and crop growth information. It was practicable to decide irrigation time with DII. With climate changing from 2003 to 2013, the frequency of irrigation times fluctuated more remarkable, and interannual drought stress took place more frequently than the past 63 years. Scientific and reasonable irrigation managements should be worked out in order to reduce the influence of drought stress on crop growth.