Net ecosystem exchange of carbon dioxide and water vapor fluxes in winter wheat and canola under conventional till and no-till systems

Abstract

It is crucial to understand the impacts of climatic and crop factors, and management practices on carbon and water dynamics of Wheat (Triticum aestivum L.) and Canola (Brassica napus L.) ecosystems for long-term water planning and improved resource use efficiencies. Net ecosystem exchange (NEE) of CO2 and H2O was measured using eddy covariance systems over neighboring wheat and canola fields with different tillage practices such as conventional till (CT) and no-till (NT) in El Reno, Oklahoma, USA. In addition, wheat fields received different grazing managements such as grain only and graze-grain. The objectives of this study were to determine the seasonality of NEE, evapotranspiration (ET), and ecosystem water use efficiency (EWUE) over wheat and canola ecosystems in response to biophysical factors and management practices. In wheat ecosystems, the results revealed that large differences in ET and EWUE were attributed to different climatic conditions and grazing management. Large differences in CO2 fluxes and ET during the canola growing season were caused by differences in stand establishment after winter dormancy rather than by tillage practices. The cumulative wheat ET was 459 mm for CT and 469 mm for NT under grain-only wheat and 365 mm for CT and 404 mm for NT under graze-grain wheat. The growing season EWUE was 3.49 (CT) and 3.27 (NT) g C mm⁻¹ ET for the grain-only and 2.82 (CT) g C mm⁻¹ ET and 2.99 (NT) g C mm⁻¹ ET for the graze-grain wheat fields. Daily ET reached 6 mm at CT and NT fields for grain-only wheat and 4.6 mm (CT) and 5.3 mm (NT) for graze-grain wheat.

The seasonal sums of NEE were -346 g C m⁻² and -188 g C m⁻² at the CT and NT canola fields. Cumulative seasonal ET during the growing season was similar for both fields (429 mm for CT and 415 mm for NT). The EWUE at the growing season scale was 2.97 and 2.78 g C mm⁻¹ ET for CT and NT canola fields, respectively. The maximum NEE (7-day average) reached -5.19 ± 0.49 and -4.66 ± 0.35 g C m⁻² d⁻¹ at CT and NT canola fields, respectively. Magnitude of daily canola ET (7-day average) reached 4.69 ± 0.42 mm d⁻¹ and 4.28 ± 0.36 mm d⁻¹ at CT and NT canola fields, respectively. This research showed the similar seasonal ET between CT and NT management and higher EWUE at CT field for grain-only wheat field under favorable conditions. The CT canola field was a strong carbon sink at the season scale. The ET were similar between CT and NT canola fields, however the higher EWUE was observed at CT field. However, long-term measurements are required to understand the influence of tillage practices and climatic conditions on carbon and ET dynamics.