Modelling the effect of aggregates on N2O emission from denitrification in an agricultural peat soil

Nitrous oxide (N2O) emissions are highly variable in time, with high peak emissions lasting a few days to several weeks and low background emissions. This temporal variability is poorly understood which hampers the simulation of daily N2O emissions. In structured soils, like clay and peat, aggregates hamper the diffusion of oxygen, which leads to anaerobic microsites in the soil, favourable for denitrification. Diffusion of N2O out of the aggregates is also hampered, which leads to delayed emissions and increased reduction of N2O to N-2. In this model simulation study we investigate the effect of aggregates in soils on the N2O emissions. We present a parameterization to simulate the effects of aggregates on N2O production by denitrification and on N2O reduction. The parameterization is based on the mobile-immobile model concept. It was implemented in a field-scale hydrological-biogeochemical model combination. We compared the simulated fluxes with observed fluxes from a fertilized and drained peat soil under grass. The results of this study show that aggregates strongly affect the simulated N2O emissions: peak emissions are lower, whereas the background emissions are slightly higher. Including the effect of aggregates caused a 40% decrease in the simulated annual emissions relative to the simulations without accounting for the effects of aggregates. The new parameterization significantly improved the model performance regarding simulation of observed daily N2O fluxes; r(2) and RMSE improved from 0.11 and 198 g N2O-N ha(-1) d(-1) to 0.41 and 40 g N2O-N ha(-1) d(-1), respectively. Our analyses of the model results show that aggregates have a larger impact on the reduction than on the production of N2O. Reduction of N2O is more sensitive to changes in the drivers than production of N2O and is in that sense the key to understanding N2O emissions from denitrification. The effects of changing environmental conditions on reduction of N2O relative to N2O production strongly depend on the NO3 content of the soil. More anaerobic conditions have hardly any effect on the ratio of production to reduction if NO3 is abundant, but will decrease this ratio if NO3 is limiting. In the first case the emissions will increase, whereas in the second case the emissions will decrease. This study suggests that the current knowledge of the hydrological, biogeochemical and physical processes may be sufficient to understand the observed N2O fluxes from a fertilized clayey peatland. Further research is needed to test how aggregates affect the N2O fluxes from other soils or soils with different fertilization regimes

Water en nutriënten gelimiteerde gewasopbrengst : koppeling van de modellen SWAP-ANIMAO-WOFOST

Dit rapport beschrijft een verkennende studie voor een methodiek waarin de bodem-nutriëntenhuishouding op dynamische wijze is gekoppeld aan gewasgroei. Voor deze studie is gewasgroei gesimuleerd met het model WOFOST, gekoppeld aan het hydrologisch model SWAP. Dit is uitgebreid met een dynamische koppeling met het biogeochemisch model ANIMO waardoor het mogelijk is terugkoppelingen tussen nutriënten, water en vegetatie te bestuderen. In een casestudie en verschillende modelexperimenten is nagegaan wat het effect is van een beperking in bodem-nutriëntenaanbod op gewasgroei en verdamping. De modelresultaten laten zien dat het veronderstelde effect van stikstoftekort op gewasgroei en verdamping aantoonbaar is en gekwantificeerd kan worden met het huidige modelinstrumentarium. Hierbij is het aanbod van water en nutriënten in detail gemodelleerd. De vraagkant vanuit het gewas is relatief eenvoudig gemodelleerd en vereist nadere studie om operationele toepassingen (bijvoorbeeld schade-berekeningen) mogelijk te maken

Significant non-linearity in nitrous oxide chamber data and its effect on calculated annual emissions

Chambers are widely used to measure surface fluxes of nitrous oxide (N2O). Usually linear regression is used to calculate the fluxes from the chamber data. Non-linearity in the chamber data can result in an underestimation of the flux. Non-linear regression models are available for these data, but are not commonly used. In this study we compared the fit of linear and non-linear regression models to determine significant non-linearity in the chamber data. We assessed the influence of this significant non-linearity on the annual fluxes. For a two year dataset from an automatic chamber we calculated the fluxes with linear and non-linear regression methods. Based on the fit of the methods 32% of the data was defined significant non-linear. Significant non-linearity was not recognized by the goodness of fit of the linear regression alone. Using non-linear regression for these data and linear regression for the rest, increases the annual flux with 21% to 53% compared to the flux determined from linear regression alone. We suggest that differences this large are due to leakage through the soil. Macropores or a coarse textured soil can add to fast leakage from the chamber. Yet, also for chambers without leakage non-linearity in the chamber data is unavoidable, due to feedback from the increasing concentration in the chamber. To prevent a possibly small, but systematic underestimation of the flux, we recommend comparing the fit of a linear regression model with a non-linear regression model. The non-linear regression model should be used if the fit is significantly better. Open questions are how macropores affect chamber measurements and how optimization of chamber design can prevent this

Beïnvloeden van landgebonden broeikasgasemissies : Naar een klimaatneutrale(re) inrichting van het landelijke gebied

Onderzocht is of mitigatie mogelijk terug te dringen is in de veenweidegebieden en of het door de vastlegging van koolstof in bossen te verhogen is. Daarnaast is bepaald wat de effecten zijn van het Nederlandse landgebruik in de toekomst (scenario's) op de broeikasemissie

Ultra-shallow junction formationby outdiffusion from implanted oxide

We present a new method for the fabrication of shallow n/sup +/ and p/sup +/ junctions in silicon. The method consists of implanting a screening oxide followed by a diffusion step to drive the dopant into the silicon. This paper reports on the electrical and physical characteristics of these shallow junctions, and it show results obtained with sub-100 nm NMOS devices fabricated with these junctions

Simulation of daily Nitrous Oxide emissions from managed peat soils

Simulation of emissions of the greenhouse gas N2O from agricultural land is still a challenge. This is mainly due to its high temporal variability, with low background emissions and a few transient peaks. In this study, a first attempt was made to simulate observations of N2O fluxes with a daily time step from managed peat soils. We used a new N2O module added to the extensively tested hydrological–biogeochemical model combination SWAP-ANIMO, hypothesizing that accurate simulation of the controlling factors would imply accurate simulation of the dynamics of the N2O emissions as well. We used daily N2O emission data from three sites in the Netherlands, with complementary data on soil moisture, mineral N content, and soil N2O concentration. Simulation of soil moisture, mineral N, and N2O concentration was reasonable to good. Still, simulation of the daily N2O emissions was poor, with model efficiencie