Detecting small-scale spatial heterogeneity and temporal dynamics of soil organic carbon (SOC) stocks: a comparison between automatic chamber-derived C budgets and repeated soil inventories

Abstract

<p><strong>Abstract.</strong> Carbon (C) sequestration in soils plays a key role in the global C cycle. It is therefore crucial to adequately monitor dynamics in soil organic carbon (∆SOC) stocks when aiming to reveal underlying processes and potential drivers. However, small-scale spatial and temporal changes in SOC stocks, particularly pronounced on arable lands, are hard to assess. The main reasons for this are limitations of the well-established methods. On the one hand, repeated soil inventories, often used in long-term field trials, reveal spatial patterns and trends in ∆SOC but require a longer observation period and a sufficient number of repetitions. On the other hand, eddy covariance measurements of C fluxes towards a complete C budget of the soil-plant-atmosphere system may help to obtain temporal ∆SOC patterns but lack small-scale spatial resolution. To overcome these limitations, this study presents a reliable method to detect both short-term temporal as well as small-scale spatial dynamics of ΔSOC. Therefore, a combination of automatic chamber (AC) measurements of CO<sub>2</sub> exchange and empirically modeled aboveground biomass development (NPPshoot) was used. To verify our method, results were compared with ΔSOC observed by soil resampling. <br><br> AC measurements were performed from 2010 to 2014 under a <i>silage maize/winter fodder rye/sorghum-Sudan grass hybrid/alfalfa</i> crop rotation at a colluvial depression located in the hummocky ground moraine landscape of NE Germany. Widespread in large areas of the formerly glaciated Northern Hemisphere, this depression type is characterized by a variable groundwater level (GWL) and pronounced small-scale spatial heterogeneity in soil properties, such as SOC and nitrogen (Nt). After monitoring the initial stage during 2010, soil erosion was experimentally simulated by incorporating topsoil material from an eroded midslope soil into the plough layer of the colluvial depression. SOC stocks were quantified before and after soil manipulation and at the end of the study period. AC-based ∆SOC values corresponded well with the tendencies and magnitude of the results observed in the repeated soil inventory. The period of maximum plant growth was identified as being most important for the development of spatial differences in annual ΔSOC. Hence, we were able to confirm that AC-based C budgets are able to reveal small-scale spatial and short-term temporal dynamics of ∆SOC.</p>

Crop growth and soil water fluxes at erosion‐affected arable sites: Using weighing lysimeter data for model intercomparison

“…This landscape type is important for global crop production, as it covers ∼10% of the arable land at the global temperate climatic zone (Chapman et al., 2020; Sommer, Fiedler, Glatzel, & Kleber, 2004). It reveals a regular, erosion‐ and deposition‐related soil pattern across continents (Pennock, Bedard‐Haughn, Kiss, & van der Kamp, 2014; Sommer, Gerke, & Deumlich, 2008) and has been intensively studied under aspects of erosion feedbacks on crop biomasses and yields (Papiernik et al., 2005), as well as on greenhouse gas fluxes (Hoffmann et al., 2017; Pennock et al., 2010). We selected lysimeter observations from four soil profiles, which differed in both soil type and soil erosion history and capture a broad range of the field‐scale spatial variability of soils in erosion‐affected, hummocky agricultural landscapes (Miller et al., 2016; Sommer et al., 2008).…”

Net ecosystem fluxes and composition of biogenic volatile organic compounds over a maize field–interaction of meteorology and phenological stages

“…In this study, we analysed changes of BVOC emissions from a maize field as a function of environmental cofactors, phenological stages, and plant status (potential heat and drought stress effects). To achieve this, we applied large automatic chamber systems, initially used to capture net ecosystem exchange (NEE) of CO 2 and evapotranspiration (Hoffmann et al, 2016). These systems allow measuring concentration differences of air chemical compounds under almost all weather conditions and the simultaneously derived carbon and water fluxes can be used to evaluate plant stress.…”

Detecting small-scale spatial heterogeneity and temporal dynamics of soil organic carbon (SOC) stocks: a comparison between automatic chamber-derived C budgets and repeated soil inventories

“…The data referred to in this study is publicly accessible at doi:10.4228/ZALF.2017.322 (Hoffmann et al, 2017). Figure A1 shows the development of important environmental variables throughout the study period (January 2010-December 2014).…”