Effects of diversified and conventional crop management on evapotranspiration, yield, and water-use efficiency measured with weighing lysimeters over six years

Cover cropping and diversified crop rotations are widely promoted as strategies to enhance soil carbon inputs and contribute to climate change mitigation. However, including additional crop cover could have detrimental impact of water use efficiency (WUE) and has not been sufficiently quantified under continuous field conditions. We evaluated two contrasting crop management systems over two full rotation cycles (2017–2022): a diversified winter wheat–corn–soybean rotation with cover crops and a conventional soybean–corn–soybean rotation without cover crops. Evapotranspiration (ET) was measured at half-hourly resolution using large weighing lysimeters at the Elora Research Station in Ontario, Canada. Analyses focused on the growing season (1 May–1 November), and cumulative seasonal ET was calculated for each lysimeter. Crop yield was measured annually, and WUE was calculated as the ratio of yield to cumulative ET. The experiment included 12 lysimeters across two soil types (silt loam and loamy sand). Across six growing seasons, cumulative ET ranged from 350 to 800 mm, yield from 903 to 13,203 kg ha⁻¹, and WUE from 0.17 to 2.1 kg m⁻³. Despite clear differences in management practices, ET, yield, and WUE did not differ significantly between the diversified and conventional systems in five of six years. In 2017, significant differences were observed between managements for ET in loamy sand soil and for yield and WUE in silt loam soil, largely reflecting differences in crop type between systems. In contrast, soil type consistently exerted a strong influence on ET, yield, and WUE across all years. These results suggest that, in the studied agroecosystem, there are minimal trade-offs between climate change mitigation benefits associated with cover crop use and the water-use efficiency of diversified cropping systems, with soil properties exerting dominant control on crop water use and productivity.