Search

In the light of the ongoing global climate crisis and the related increases in extreme hydrological events, it is crucial to assess ecosystem resilience and – in agricultural systems – to ensure sustainable management and food security. For this purpose, a comprehensive understanding of ecosystem water cycle budgets and spatiotemporal dynamics is indispensable. Evapotranspiration (ET) plays a pivotal role in returning up to 90 % of incoming precipitation back to the atmosphere. Here, we studied the impacts of soil types and management on an agroecosystem's seasonal cumulative ET (ET sum) and agronomic water use efficiency (WUE agro , the dry matter per unit of water used by the crop). To do so, a plot experiment with winter rye (17 September 2020 to 30 June 2021) was conducted in an eroded cropland which is located in the hilly and dry ground moraine landscape of the Uckermark region in northeastern Germany. Along the experimental plot (110 m × 16 m), two closed chambers were mounted on a robotic gantry crane system (FluxCrane as part of the AgroFlux platform) and used to determine ET. Three soil types representing the full soil erosion gradient related to the hummocky ground moraine landscape (extremely eroded: Calcaric Regosol; strongly eroded: Nudiargic Luvisol; non-eroded: Calcic Luvisol) and additional topsoil dilution (topsoil removal and subsoil admixture) were investigated (randomized block design, three replicates per treatment). Five different modeling approaches were used and compared in the light of their potential for reliable ET sum over the entire crop cultivation period and to reproduce short-term (e.g., diurnal) water flux dynamics. While machine-learning approaches such as support vector machines (SVMs) and artificial neural networks (with Bayesian regularization; ANN_BR) generally performed well during calibration, SVMs also provided a satisfactory prediction of measured ET during validation (k -fold cross-validation, k=5). We found significant differences in dry biomass (DM) and small trends in ET sum between soil types, resulting in different WUE agro. The extremely eroded Calcaric Regosol showed an up to 46 % lower ET sum and up to 54 % lower WUE agro compared to the non-eroded Calcic Luvisol. The key period contributing to 70 % of ET sum spanned the beginning of stem elongation in April to the harvest in June. However, differences in the ET sum between soil types and topsoil dilution resulted predominantly from small differences between the treatments throughout the cultivation rather than only during this short period of time. [ABSTRACT FROM AUTHOR]

• Soil erosion states strongly impact N 2 O emission similar to N fertilizer form. • Organic fertilizer resulted in highest N 2 O emission compared to mixed and mineral. • Depositional soil resulted in highest N 2 O emission compared to non-eroded and eroded. • Site-specific differences in soil properties induced by erosion influence N 2 O emission. Soil erosion affects 20% of croplands worldwide. However, understanding the effect of soil erosion on N 2 O emissions, which is one of the most potent greenhouse gases, is still limited. This limitation is likely because the small-scale differences in soil properties and fertility induced by erosion (i.e. ranges of erosion states) have barely been considered in studies quantifying N 2 O emissions from croplands. There are, however, indications that the erosion state itself strongly impacts N 2 O emission, similar to the N fertilizer form. Therefore, our investigations aimed to further explore these indications. We measured N 2 O fluxes for three years and at five sites within an erosion affected field experiment. N 2 O emissions were quantified using a manual chamber system. Three sites were established on a summit position (Albic Luvisol; non-eroded) but differed in N fertilizer forms (organic biogas fermented residues, calcium ammonium nitrate and a mixture of both fertilizers). Two additional sites were established on an extremely eroded soil (Calcaric Regosol) and wet depositional soil in a depression (Endogleyic Colluvic Regosol) to measure the effect of soil erosion states on N 2 O emissions. Both additional sites were fertilized with calcium ammonium nitrate only. In case of the non-eroded soil (summit), organic fertilization resulted in the highest cumulative N 2 O emission (6.2 ± 0.21 kg N 2 O-N/ha y−1) compared to mixed (5.5 ± 0.18 kg N 2 O-N/ha y−1) and mineral (1.9 ± 0.17 kg N 2 O-N/ha y−1) fertilization. These high emissions were probably caused by soluble C and N substrates from organic fertilizer, resulting in microbial activities favoring high N 2 O emissions. Regarding the erosion status, we observed the highest N 2 O emissions in the depositional soil (2.8 ± 0.21 kg N 2 O-N/ha y−1), followed by the non-eroded (1.9 ± 0.17 kg N 2 O-N/ha y−1) and the extremely eroded soil (0.6 ± 0.03 kg N 2 O-N/ha y−1). These differences in N 2 O emissions were mainly due to the site-specific, erosion induced differences in soil properties such as soil texture, soil organic C and total N contents and stocks, water-filled pore space and soil pH. These results indicate that soil erosion state may indeed be of similar importance, as N fertilizer form, for the magnitude of N 2 O emissions from croplands. [ABSTRACT FROM AUTHOR]

• Novel robotic chamber for high small-scale spatial resolution of GHG emissions • Reliability of robotic chamber is shown for CO 2 emissions based on sample dataset • Temporal dynamics of CO 2 emissions were influenced by phenology/weather and management • Spatial pattern of CO 2 emissions were influenced mainly by soil types The precise and accurate assessment of carbon dioxide (CO 2) exchange is crucial to identify terrestrial carbon (C) sources and sinks and for evaluating their role within the global C budget. The substantial uncertainty in disentangling the management and soil impact on measured CO 2 fluxes are largely ignored especially in cropland. The reasons for this lies in the limitation of the widely used eddy covariance as well as manual and automatic chamber systems, which either account for short-term temporal variability or small-scale spatial heterogeneity, but barely both. To address this issue, we developed a novel robotic chamber system allowing for dozens of spatial measurement repetitions, thus enabling CO 2 exchange measurements in a sufficient temporal and high small-scale spatial resolution. The system was tested from 08th July to 09th September 2019 at a heterogeneous field (100 m × 16 m), located within the hummocky ground moraine landscape of northeastern Germany (CarboZALF-D). The field is foreseen for a longer-term block trial manipulation experiment extending over three erosion induced soil types and was covered with spring barley. Measured fluxes of nighttime ecosystem respiration (R eco) and daytime net ecosystem exchange (NEE) showed distinct temporal patterns influenced by crop phenology, weather conditions and management practices. Similarly, we found clear small-scale spatial differences in cumulated (gap-filled) R eco , gross primary productivity (GPP) and NEE fluxes affected by the three distinct soil types. Additionally, spatial patterns induced by former management practices and characterized by differences in soil pH and nutrition status (P and K) were also revealed between plots within each of the three soil types, which allowed compensating for prior to the foreseen block trial manipulation experiment. The results underline the great potential of the novel robotic chamber system, which not only detects short-term temporal CO 2 flux dynamics but also reflects the impact of small-scale spatial heterogeneity. Image, graphical abstract [ABSTRACT FROM AUTHOR]