Effects of Climatic Conditions and Management Practices on Agricultural Carbon and Water Budgets in the Inland Pacific Northwest USA. Issue 12 (14th December 2017) - Chi, Jinshu
Abstract: Cropland is an important land cover influencing global carbon and water cycles. Variability of agricultural carbon and water fluxes depends on crop species, management practices, soil characteristics, and climatic conditions. In the context of climate change, it is critical to quantify the long‐term effects of these environmental drivers and farming activities on carbon and water dynamics. Twenty site‐years of carbon and water fluxes covering a large precipitation gradient and a variety of crop species and management practices were measured in the inland Pacific Northwest using the eddy covariance method. The rain‐fed fields were net carbon sinks, while the irrigated site was close to carbon neutral during the winter wheat crop years. Sites growing spring crops were either carbon sinks, sources, or neutral, varying with crops, rainfall zones, and tillage practices. Fluxes were more sensitive to variability in precipitation than temperature: annual carbon and water fluxes increased with the increasing precipitation while only respiration increased with temperature in the high‐rainfall area. Compared to a nearby rain‐fed site, irrigation improved winter wheat production but resulted in large losses of carbon and water to the atmosphere. Compared to conventional tillage, no‐till had significantly lower respiration but resulted in slightly lower yields and water use efficiency over 4 years. Under future climate change, it is expected that more carbon fixation by crops and evapotranspiration would occur in a warmer and wetter environment. Plain Language Summary: Croplands play an important role in global carbon and water cycles. Agricultural carbon and water budgets are affected by crop species, management practices, and climatic and soil conditions. In the context of climate change, it is critical to investigated the long‐term effects of these environmental drivers and farming activities on carbon and water dynamics. Carbon and water budgets covering a large precipitation gradient and a variety of crop species and management practices were measured in the inland Pacific Northwest (iPNW) region. Winter wheat growing under the rain‐fed conditions had more net carbon gain versus the irrigated conditions. Sites growing spring crops were either uptaking or emitting carbon, or in carbon balance annually. The annual net carbon gain magnitudes increased in the following order: spring garbanzo, spring barely, spring pea, spring canola, spring wheat, potatoes, and winter wheat. Irrigation can improve crop production but result in large losses of carbon and water to the atmosphere. Adoption of no‐till can mitigate CO2 emissions but may cause lower yields and water use efficiency. Carbon and water dynamics are more sensitive to variability in precipitation than temperature in the iPNW. Under future climate change, more carbon fixation by crops and evapotranspiration would occur in a warmer and wetter environment. Key Points: The rain‐fed fields were net carbon sinks, while the irrigated site was close to carbon neutral during the winter wheat crop years Compared to conventional tillage, no‐till had significantly lower respiration but resulted in lower yields and water use efficiency Fluxes were more sensitive to variability in precipitation than temperature; GPP and ET would increase in a warmer and wetter environment