Climate Change Predicted to Negatively Influence Surface Soil Organic Matter of Dryland Cropping Systems in the Inland Pacific Northwest, USA

Abstract

Soil organic matter (SOM) is a key indicator of agricultural productivity and overall soil health. Currently, dryland cropping systems of the inland Pacific Northwest (iPNW) span a large gradient in mean annual temperature (MAT) and precipitation (MAP). These climatic drivers are major determinants of surface SOM dynamics and storage characteristics. Future climate change projections through 2070 indicate significant shifts in MAT and MAP for the iPNW. We assessed surface (0-10 cm) soil organic C and N as well as active and recalcitrant fractions of SOM within long-term experiments representing different tillage regimes and cropping intensities across the current climatic gradient of the iPNW. We discovered that current levels of soil C and N as well as various SOM fractions were positively correlated with MAP and negatively correlated with MAT. Furthermore, these climatic drivers were more influential than either tillage regime or cropping intensity in determining SOM levels and characteristics. Soil organic C and total N as well as the hydrolyzable and non-hydrolyzable fractions were negatively correlated with the current ratio of MAT to MAP, called the climate ratio. Future climate projections (2030 and 2070) forecast an increase of the climate ratio, thus predicting declines in surface SOM and associated soil health across the iPNW.

Impact of Climate Change Adaptation Strategies on Winter Wheat and Cropping System Performance across Precipitation Gradients in the Inland Pacific Northwest, USA

“…Earthworms may be observed above 330-370 mm of mean annual precipitation (Walsh and Johnson-Maynard, 2016), and soil organic matter increases in the topsoil (Morrow et al, 2017). We determined that WW yields reached a maximum of 6,800 kg ha −1 at 520 mm yr −1 , within the annual cropping region where precipitation is adequate to economically support crops every year (Figure 2A).…”

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

“…Under the warmer conditions in the future, CO 2 emissions from agriculture could increase in the high-rainfall areas in this region. Correspondingly, Morrow, Huggins, and Reganold (2017) found that soil organic matter in this region would decrease as a result of temperature increases. The regional precipitation would also increase by 5-15% with wetter winters and springs as well as drier summers , which might result in a greater magnitude of carbon uptake and evapotranspiration in both high-and low-rainfall areas.…”

“…Based on model projections, other dynamic AECs (e.g., dynamic annual crop-fallow or dynamic grain-fallow) may increase (~60%) and result in more fallow management practice under future climate scenarios, although the counteracting effect of increasing atmospheric CO 2 concentration was not accounted for in their study (Kaur et al, 2017). On the other hand, climate change is predicted to have negative effects on soil health characteristics in the iPNW region (Morrow et al, 2017), which may directly affect carbon and water dynamics. Under these circumstances, studies at the expanding dynamic AECs as well as under different soil management conditions will be critical to understand the regional carbon and water budgets in the future, as the baseline measurements in this study can be utilized as analogs for future scenarios.…”

Northwest U.S. Agriculture in a Changing Climate: Collaboratively Defined Research and Extension Priorities

“…Another significant concern is that climate change may cause farmers to increase fallowing as a risk mitigation strategy in the dryland crop production areas of the inland Northwest. This could threaten decades of progress made in reducing soil erosion, and make maintaining SOC more challenging (Kaur et al, 2017;Morrow et al, 2017). Similarly, some strategies to limit emissions of N 2 O could increase losses of nitrogen as ammonia or nitrate.…”