Evapotranspiration and crop coefficient of spring maize with plastic mulch using eddy covariance in northwest China

Spring maize under plastic mulch is the staple food crop in northwest China. Studying its evapotranspiration (ET) and crop coefficient (Kc) is important for managing water-saving irrigation in the region. Eddy covariance (EC) was applied to measure spring maize ET in 2007 in northwest China, focusing on the characteristics of the maize ET and Kc processes under plastic mulch. An interesting result was that a higher Kc in this study relative to the value of FAO 56 was presented in the mid and late season, e.g. average Kc was 1.46, 1.39 and 1.22 during the heading, filling and maturity stage, respectively. This result was mainly due to that (1) the plastic mulch had an effect on anti-senescence of maize and great green leaf still existed before the harvest; (2) the FAO 56 PM model may underestimate the reference crop ET in the mid and late season of maize in the region; (3) the planting density was higher in the study, which was about 374,800 plants ha-1. Though Kc during the mid and late season was high, a high water use efficiency of 25.2 kg ha-1 mm-1 was still obtained in the study. Our study confirmed that plastic mulch has beneficial effect on improving maize water use efficiency in this severe water shortage region of northwest China.