A Comparison of Daily and Hourly Evapotranspiration and Transpiration Rate of Summer Maize with Contrast Canopy Size

Detailed characterization of evapotranspiration (ET) patterns is crucial for optimizing irrigation scheduling and enhancing water use efficiency in the North China Plain. A two-season study conducted at the National Experimental Station for Precise Agriculture in Beijing compared summer maize varieties with contrasting canopy sizes (JK: large canopy; CF: small canopy) using 12 weighing lysimeters. The results revealed: (1)seasonal ET patterns: daily average ET rates showed consistent variation between cultivars, with JK exhibiting higher water consumption, the highest daily ET of JK and CF reach 5.91 mm/day and 5.52 mm/day at V13-R1 stage in the first growth season and reach 5.21 mm/day and 5.22 mm/day at R1-R3 stage in the second growth season, respectively. (2)Diurnal dynamics: hourly ET fluctuations displayed similar temporal patterns across growth stages, regardless of canopy size. The most pronounced inter-varietal ET differences occurred during the R1-R3 reproductive stages when both cultivars maintained peak canopy development (Leaf area index(LAI) > 4.5). Notably, ET differences between JK and CF followed characteristic diurnal "increase-decrease" pattern, peaking in mid-morning (09:00-11:00) and early afternoon (13:00-15:00), with minimal divergence at solar noon. (3)Transpiration differentiation: pooled data analysis identified two critical periods driving cumulative ET differences: 12:00-17:00 during R1-R3 (anthesis) and 08:00-16:00 during R3-R5 (grain filling). JK maintained significantly higher transpiration rates (Tr), particularly during morning hours (09:00-12:00), with mean Tr exceeding CF by 5.3% (pre-anthesis) and 16.0% (post-anthesis).The observed Tr differentials suggest that canopy architecture modulates stomatal regulation patterns, with large-canopy genotypes demonstrating greater morning photosynthetic activity but similar midday water conservation strategies. Our findings reveal the relationship between the leaf area index and evapotranspiration of summer maize across multiple timescales, including periodic, daily, and hourly variations. This study provides valuable data to support precise and quantitative irrigation strategies for maize production in the region.