Carbon and water dynamics of a perennial versus an annual grain crop in temperate agroecosystems

Abstract

Interest in novel perennial grain crops has increased as a sustainable alternative to conventional annual grain crops due to their improved carbon (C) sequestration and water use efficiency potentials. This study quantified carbon dioxide (CO2) and water fluxes over contrasting cropping systems: a perennial crop (i.e., Secale cereale L. × S. montanum Guss cv. ACE-1 perennial rye) vs. an annual crop (i.e., S. cereale L. cv. Gazelle spring rye). The experiment was conducted over two growing seasons (May to October) using eddy covariance system measurements in two adjacent 4-ha fields in Breton, Alberta, Canada. Substantially greater uptake of atmospheric C was observed in the perennial crop compared to the annual crop, as shown by growing season net ecosystem CO2 exchange of 556 g C m−2 yr−1 in the perennial crop vs. only 89 g C m−2 yr−1 in the annual crops. Net ecosystems carbon balances (NECB) of -60 and 448 g C m−2 were either C neutral or C gain in perennial crops, while NECB of -263 and -336 g C m−2 in annual crops were C losses during the two growing seasons. Overall, the ecosystem carbon use efficiency of the perennial crop was also greater than that of the annual crops. In addition to the longer growing period of the perennial crop, which enhanced the cumulative C captured via photosynthesis, the greater CO2 sink was attributed to relatively lower ecosystem respiration, which was influenced by soil temperature sensitivity, reduced soil disturbance, and soil moisture factors. Despite the perennial crop registering higher evapotranspiration (ET) at the beginning of growing season, the overall cumulative ET and the associated ecosystems-water use efficiency were similar between the two crops. As such, the perennial crop enhanced atmospheric CO2 sink compared to annual crop, whereas the terrestrial water balance was similar between two crops.