Temporal and spatial distribution characteristics of maize water surplus deficit and irrigation mode partition in Liaoning province

Abstract: It is necessary to formulate a partition irrigation management mode based on the feature of water resource and meteorology of different sub areas in a large area. Maize is the main crop and major agricultural water consumer in Liaoning province. The objective of this study was to analyze the temporal and spatial distribution characteristics of maize water surplus deficit and lay out an irrigation mode partition scheme in Liaoning province. We collected the data of maize growth index, irrigation, and daily meteorological data from 1955 to 2014 in 27 agricultural meteorological stations in Liaoning province. The calculated index included evapotranspiration (ET), irrigation requirement, crop water surplus and deficit index (CWSDI)?the drought probability during the maize growth stage in Liaoning. The results showed that: the ET during the growth stage of maize varied in a single peak style in all the regions of Liaoning. The ET in western Liaoning was the highest in Liaoning, and the monthly ET of the western Liaoning was more than 140 mm in July. The high value of ET mainly appeared in the western region (ET≥380 mm). The ET was lower in the central and southern regions in Liaoning. The minimum value of ET was in the southern Liaoning, which was less than 345 mm. The standard deviation of ET were higher in the central and southern Liaoning around the Bohai sea (SD>15 mm), but it were stable in eastern and western Liaoning (SD<8 mm). A total of 4 typically deficient irrigation schedule were recommended and the irrigation norm in different hydrological years were 40, 80, 120 and 135 mm, respectively for the wet year, the normal year, the dry year and the drought year. In most years, CWSDI of maize were above 0 in the eastern Liaoning, and the peak was above 2.5 (in the year of 1985). It indicates that the crop water supply exceeded demand in most of years. It was significantly different between the western and eastern Liaoning. In the western Liaoning, the most of the CWSDI was below 0, and sometimes even below (0.14. There was a widespread mild dry in most of the years, sometimes was dry even drought in this region. The spatial distribution of the dry frequency indicated that, in addition to the southeast Liaoning, the most regions may become mild dry, dry or drought, most especially in the western Liaoning. In the northwest Liaoning, the frequency of mild drought occurrence was high. The dry mainly appeared in the western Liaoning. The CWSDI and the dry frequency had the similar spatial distribution pattern. The area with mild dry frequency not less than 0.45, dry frequency not less than 0.28, the drought frequency not less than 0.12 and CWSDI higher than 0 was same. Thus, we defined the area meeting one of the conditions above as the arid area. Those areas were in the western and northern Liaoning where the water resource supply was less than demand and the dry condition appeared very often. We defined the area with mild dry frequency not less than 0.1 or CWSDI higher than 0.45 as the drouht-prone area. These areas were in the northern Liaoning, middle Liaoning and the west of eastern Liaoning. Based on the CWSDI and dry frequency, a total of 7 irrigation modes were set up. A total of 6, 4, 3 and 1 irrigation mode were for the drought, dry, normal and wet year, respectively. The study would improve not only the areas water resource utilization but also food security.