Irrigation Scheduling with Soil Gas Diffusivity as a Decision Tool to Mitigate N2O Emissions from a Urine-Affected Pasture

Pastures require year-round access to water and in some locations rely on irrigation during dry periods. Currently, there is a dearth of knowledge about the potential for using irrigation to mitigate N2O emissions. This study aimed to mitigate N2O losses from intensely managed pastures by adjusting irrigation frequency using soil gas diffusivity (Dp/Do) thresholds. Two irrigation regimes were compared; a standard irrigation treatment based on farmer practice (15 mm applied every 3 days) versus an optimised irrigation treatment where irrigation was applied when soil Dp/Do was ≈0.033 (equivalent to 50% of plant available water). Cow urine was applied at a rate of 700 kg N ha−1 to simulate a ruminant urine deposition event. In addition to N2O fluxes, soil moisture content was monitored hourly, Dp/Do was modelled, and pasture dry matter production was measured. Standard irrigation practices resulted in higher (p = 0.09) cumulative N2O emissions than the optimised irrigation treatment. Pasture growth rates under treatments did not differ. Denitrification during re-wetting events (irrigation and rain) contributed to soil N2O emissions. These results warrant further modelling of irrigation management as a mitigation option for N2O emissions from pasture soils, based on Dp/Do thresholds, rainfall, plant water demands and evapotranspiration.

Effects of liming on soil structure and GHG fluxes at three spruce sites in SW Germany

<p>Forest soils in Central Europe received massive atmospheric deposition of SO<sub>2</sub> and NO<sub>x</sub> during the second half of the 20<sup>th</sup> century. The resulting fast acidification of the soils was accompanied by massive forest dieback and problematic nutrient imbalances at some sites. After the emissions of SO<sub>2</sub> have been reduced in the 80´s and 90´s, the situation of acidic deposition has been gradually improving. Yet, the deposition of N compounds remains high and still has an impact on forest ecosystems. Natural soil development and “regeneration” is a slow process, which is why other options were investigated to recover heavily affected forest soils. A well-known means to mitigate the observed effects of the anthropogenic acidification surges is liming, i.e. the application of minerals such as CaCO<sub>3</sub> and CaMg(CO<sub>3</sub>)<sub>2</sub> that are able to buffer strong acids. Liming directly affects soil pH which is a “master variable” of the soil. Soil pH, and thus, liming, affects and interacts with many soil processes from mineralization of organic matter and humification, to (de-) stabilization soil structure, nutrient availability and mobility, plant growth and more.</p><p>Several study sites were established in the 1980 in Baden-Wuerttemberg to study long term effects of liming on soil structure and forest growth. At all sites a “control” plot and a “limed” plot were established next to each other. The limed plots were treated with approx. 3 t ha<sup>-1</sup> of CaCO<sub>3</sub> in the 1980´s and 6 t ha<sup>-1</sup> of Ca/MgCO<sub>3 </sub>in 2003. Here we report on results from three sites (Bad Waldsee, Hospital, Herzogenweiler) with Spruce stands (70-110 years), where long term effects of liming on the physical soil structure and soil gas profiles (2017-2019) were studied (Jansone et al., 2020). Liming resulted in a reduction of the thickness of the humus layer and a blurring of the previously clearly separated boundary between the mineral soil and the humus layer. Even though total pore space in the top soil was slightly reduced at the limed plots, soil gas diffusivity was higher at a given air-filled pore-space. This indicates a better connectivity in the air-filled pores, that means more larger pores connecting the atmosphere at the soil surface and the mineral soil. Soil CO<sub>2</sub> concentrations showed clear seasonal patterns and a typical increase with depth. Higher CO<sub>2</sub> concentrations tend to be found in the un-limed control plots. Soil CH<sub>4</sub> concentrations at the soil–humus interface were closer to atmospheric concentrations in the limed plots compared to the control plots. This can be interpreted as an effect of the decrease in the thickness of the humus layer and the increase in the soil gas diffusivity (better aeration) or in a reduced activity of the methanotrophic community.</p><p> </p><p>Acknowledgement</p><p>This research was financially supported by Bundesministerium für Ernährung und Landwirtschaft (BMEL), grant number 28W-B-4-075-02 (2018–2021).</p><p><em>Literature</em></p><p><em>Jansone, L., von Wilpert, K. and Hartmann, P., 2020. Natural Recovery and Liming Effects in Acidified Forest Soils in SW-Germany. Soil Systems, 4(38): 1-35.</em></p>

Characterization of Wetting of Deep Silica Nanoholes by Aqueous Solutions Using ATR-FTIR

In advanced semiconductor manufacturing, deep hydrophilic nanoholes are found in various applications, which require a wet clean after patterning. In this work, we use an in-situ ATR-FTIR spectroscopy technique to characterize the wetting of nanoholes in a silica matrix by UPW and electrolyte solutions. Wetting was much slower than predicted by a numerical model, while temperature cycling evidenced the formation of unexpectedly stable gas pockets in the wetted nanoholes. Water structuring in the nanoholes was characterized by an analysis of the OH stretching peak. Besides, monitoring the dissolution of CO2 in the wetted nanoholes allowed to compare the diffusivity in the nano-confined solutions with that in bulk solutions. Our results strongly suggest that the gas pockets were stabilized by the decreased gas diffusivity resulting from water structuring.

Application of magnetic field to CO hydrogenation using a confined-space catalyst: effect on reactant gas diffusivity and reactivity

Synergy between an external magnetic field and limited mass transfer within zeolite cavities leads to different diffusion abilities of CO and H2 during the reaction within the catalyst pores, leading to significant improvement in CO conversion.