Assessing crop coefficients for Zea mays in the semi-arid Hailiutu River catchment, northwest China

To improve irrigation water-use efficiency, plant transpiration and soil evaporation in a maize (Zea mays L.) field in the Bulang sub-catchment of the Hailiutu River catchment in Northwest China were determined using in situ measurements. Crop transpiration (Tp) rates from Jul 15 to Oct 1, 2011 were measured with sap flow sensors, and soil evaporation (Ep) rates were measured with micro-lysimeters under an absence of water deficit. The two rates together gave the total evapotranspiration (ETc) of the maize field. Cumulative Tp and Ep were 245 and 85 mm, accounting for 74 and 26% of total ETc (330 mm), respectively. To calculate the total ETc rate of the maize field for the entire growing season, the Penman–Monteith equation combined with a single crop coefficient method (FAO-56) was used. The estimated crop coefficient (Kc) was calibrated using actual sap flow and soil evaporation data to provide accurate estimates of actual evapotranspiration. The total crop ETc of the maize field for the 2011 and 2012 growing seasons was 583 and 500 mm, respectively, with a mean daily value of ∼4 mm d−1. Groundwater contributed 33% of the maize ETc in 2011 (average groundwater table of 1.12 m with full irrigation) and 27% in 2012 (average groundwater table of 0.89 m with full irrigation). These results will improve precise planning and efficient management of irrigation for maize in this region.