Agroecosystems Lab

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Landscape-scale Control of Spatiotemporal Variability of Soil Organic Carbon and Nitrogen Dynamics in a Tilled and Conservation Tilled Agroecosystems

photo of goatsIncrease in atmospheric CO2 and other greenhouse gases (GHG) and its resulting global warming are of international concern. Warming is expected to dramatically alter C and N cycling and ecosystem functioning. Since agriculture and related land-uses are major anthropogenic sources for atmospheric CO2, N2O and CH4, some management options have been proposed to mitigate GHG emissions from agriculture. One mitigation option is enhancing the amount of C and N sequestered in soil organic matter (SOM) by implementing conservation tillage, such as minimum tillage and no-till.

photo of wheat samplingThe level of SOM tends to increase over time after conversion to MT from standard tillage due to improved soil stability, regardless of some adverse effects (e.g., increased N2O fluxes in both dry and humid climates). Overall, increased C and N sequestration in the soil would mitigate GHG emissions and potentially slow increasing global warming from other anthropogenic sources. Many studies have investigated the influence of conservation tillage on SOM levels in the Great Plains and Corn Belt Regions, but there have been very few studies in CA agricultural systems. In general, CA has a lower mitigation potential compared to other regions.

photo of Juhwan on wheat fieldThe scale-dependent spatial and temporal variability of GHG emissions has stimulated efforts to accurately estimate the net flux of CO2, N2O and CH4. Thus, to assess the mitigation potential of conservation tillage management, landscape-scale variation as an integral source of information can be used to test and improve agricultural management. However, the magnitude of tillage-induced changes in GHG emissions across sites and regions are poorly quantified and understood under Mediterranean climate conditions. Because of the uncertainty in the emission estimates, there is a strong need for determining the impacts of conservation tillage on the nature of interactions among biotic and abiotic factors that ultimately control GHG emissions and account for their spatial and temporal variability. The patterns and related processes must be also understood within landscapes in order to understand a system’s response to tillage management.

I hypothesize that increased short-term (< 5 yr) C and N sequestration, induced by conservation tillage, leads to a spatial and temporal reduction in net flux of CO2, N2O and CH4 across the furrow-irrigated agricultural landscape. The objectives of this project are 1) to identify and quantify a set of biotic and abiotic factors controlling soil C and N sequestration across the landscape under minimum and standard tillage, and 2) to determine tillage-induced changes on key factors and their interactions responsible for short-term changes in the flux of CO2, N2O and CH4.