Effects of Climatic Conditions and Management Practices on Agricultural Carbon and Water Budgets in the Inland Pacific Northwest USA

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.

Potential greenhouse gas reductions from Natural Climate Solutions in Oregon, USA

“…Cumulative GHG reductions over the 30-year period of our analysis, reported as the median with 90% confidence interval lower and upper estimates in parenthesis, ranged from 72.2 (63)(64)(65)(66)(67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81) to 222 (184-260) MMTCO 2 e in the Limited and Ambitious scenarios, respectively (Fig 4). The Moderate scenario resulted in cumulative reductions of 123 (104-142) MMTCO 2 e by 2050.…”

“…No consensus exists on the effects of no-till on SOC in the PNW with at least two studies finding no significant effect of tillage on SOC [62,63]. However, in other studies, SOC was estimated to increase by 0.12 to 0.53 MTCO 2 e ha -1 yr -1 when switching from conventional tillage to no-till [59,64,65] and no-till did not negatively affect wheat yield [66]. PNW estimates are on the low end of average soil C sequestration rates, which tend to be lowest in cold northern and arid western states [60,67,68].…”

Interannual variability in net ecosystem carbon production in a rain-fed maize ecosystem and its climatic and biotic controls during 2005–2018

“…Vegetation phenology advance with the increasing spring precipitation and effective accumulated air temperature can lead to a decrease in CRP _begin . However, soil respiration was less sensitive to spring precipitation and temperature, due to a cover of organic residues on the soil at a no-till site [56].…”

“…The increase in spring precipitation and the effective accumulated temperature can lead to advancement of vegetation phenology [23]. Autumn phenology was dominated by autumn SWC, and soil water supply enabled carbon gain longer in the autumn [56]. The advancement of BDOY and delay of EDOY increase the length of the growing season in warmer and wetter years, and that affects the cumulative sum of assimilated carbon and NEP [17].…”

“…Although soil temperature was highly correlated to air temperature (y = 0.65x, R 2 = 0.78, P <0.001) in winter, the correlation between the two parameters in spring decreased (y = 1.25x-0.02, R 2 = 0.55, P <0.001). Residues cover from a previous year might inhibit the increases in soil temperatures in spring (y = -0.01x+7.72, R 2 = 0.34, P <0.001, S4 Fig) , and reduce soil respiration rates [56]. Vegetation phenology advance with the increasing spring precipitation and effective accumulated air temperature can lead to a decrease in CRP _begin .…”