Simulation of effect of climate, soils and management on N2O emission from grassland

Nitrous oxide (N2O) is a potent greenhouse gas with a high contribution from agricultural soils and emissions that depend on soil type, climate, crops and management practices. The N2O emissions therefore need to be included as an integral part of environmental assessment of agricultural production systems. A dynamical algorithm for N2O production and emission from agricultural soils was developed and included in the FASSET whole-farm model. The model simulated carbon and nitrogen (N) turnover on a daily basis. Both nitrification and denitrification was included in the model as sources for N2O production, and the N2O emissions were simulated to depend on soil microbial and physical conditions. The model was tested on experimental data of N2O emissions from grasslands in UK, Finland and Denmark, differing in climatic conditions, soil properties and management. The model simulated the general time course of N2O emissions and captured the observed effects of fertiliser and manure management on emissions. However, emissions from a soil with high clay content were overestimated with the model. Scenario analyses for grazed and cut grasslands were conducted to evaluate the effects of soil type, climatic conditions, grassland management and N fertilisation on N2O emissions. The soils varied from sandy to sandy loam and the climatic variation was taken to represent the climatic variation within Denmark. N fertiliser rates were varied from 0 to 500 kg N ha-1. The simulated N2O emissions showed a non-linear response to increasing N rates with increasing emission factors at higher N rates. The simulated emissions increased with increasing soil clay contents. There was no effect of climatic conditions. Emissions were slightly higher from grazed grasslands compared with cut grasslands at similar rates of total N input (fertiliser and animal excreta). The results indicate higher emission factors and thus higher potentials for reducing N2O emissions for intensively grazed grasslands on fine textured soils than for extensive cut based grasslands on sandy soils

Models meet data: Challenges and opportunities inimplementing land management in Earth system models

As the applications of Earth system models (ESMs) move from general climate projections toward questions of mitigation and adaptation, the inclusion of land management practices in these models becomes crucial. We carried out a survey among modeling groups to show an evolution from models able only to deal with land‐cover change to more sophisticated approaches that allow also for the partial integration of land management changes. For the longer term a comprehensive land management representation can be anticipated for all major models. To guide the prioritization of implementation, we evaluate ten land management practices—forestry harvest, tree species selection, grazing and mowing harvest, crop harvest, crop species selection, irrigation, wetland drainage, fertilization, tillage, and fire—for (1) their importance on the Earth system, (2) the possibility of implementing them in state‐of‐the‐art ESMs, and (3) availability of required input data. Matching these criteria, we identify “low‐hanging fruits” for the inclusion in ESMs, such as basic implementations of crop and forestry harvest and fertilization. We also identify research requirements for specific communities to address the remaining land management practices. Data availability severely hampers modeling the most extensive land management practice, grazing and mowing harvest, and is a limiting factor for a comprehensive implementation of most other practices. Inadequate process understanding hampers even a basic assessment of crop species selection and tillage effects. The need for multiple advanced model structures will be the challenge for a comprehensive implementation of most practices but considerable synergy can be gained using the same structures for different practices. A continuous and closer collaboration of the modeling, Earth observation, and land system science communities is thus required to achieve the inclusion of land management in ESMs

Modelling of N2O emissions from grasslands in Denmark

A dynamic algorithm to simulate the N2O production and emission from nitrification and denitrification has been included in the field component of the FASSET whole-farm model. Firstly, the model was tested on experimental data of N2O emissions from typical North European grasslands with mineral soils (Denmark, Finland, UK), differing in climatic conditions, soil properties and management. A good agreement was obtained between simulated and measured seasonal N2O emissions grazed and mown grasslands. The predicted annual N2O emissions were generally in accordance with the emission factor of 1.25% suggested by IPCC. Secondly, the model was tested under different climatic and management scenarios applicable for Denmark. The reasonable calculations of potent N2O emissions were done for a 4-year rotation with one year of spring barley undersown with grass, two years of grass and a forth year of barley undersown with grass. The grasslands were considered to be either grazed with heifers and treated as a cut based system (4 cuts per year), with removal of the grass production. The level of applied mineral N (ammonium nitrate, 50:50) ranged from 0 to 500 kg ha-1. For estimation of average results, 30 independent calculations with the original climatic and soil datasets were done for 3 sites in Denmark. The results showed that denitrification was always an important source for N2O emissions, increasing with increasing of denitrification rates for soils with higher clay content and N input. The emissions increased for a climate with a higher rainfall. Nitrification became a significant source for N2O emissions only in very sandy soils, losing importance for the grazed treatment faster than for cut treatments. There was almost no available N source for N2O emission during the period from late autumn to early spring. For the annual N2O emissions there was no clear climate effect between different sites. Nevertheless, for daily dynamics the higher N2O emission peaks were clearly determined by the weather pattern. For the grazed treatments N2O emissions were higher than for cut treatments with the same mineral N input. Emissions increased in a non-linear way for both the grazed and the cut treatments with relatively higher emissions at higher N inputs. There were also considerable differences between different soil types. These effects suggest that the simple IPCC methodology is not directly applicable to evaluate N2O emissions from grasslands

Udledning af lattergas fra græsmarker øges ved afgræsning og gødskning

Danmark har underskrevet Kyoto-protokollen, som forpligter til en reduktion i samfundets udledning af drivhusgasser på 21 procent i perioden fra 1990 til 2010. Med hensyn til reduktion af landbrugets udledning af drivhusgasser har fokus hidtil været på reduktion af kvælstofanvendelsen. I den nationale opgørelse beregnes lattergasudledningen som 1,25 procent af den udbragte kvælstofmængde. De nye modelberegninger, som præsenteres her, viser at dette er en alt for simpel måde at beregne lattergasudledningen på. Der er dels store forskelle mellem jordtyper, og dels er den procentvise udledning større ved høje kvælstofniveauer end ved lave niveauer. Det sidste forhold kan gøre økologisk jordbrug interessant som redskab i klimapolitikken, da kvælstofniveauet generelt er lavere i økologisk jordbrug. Der er dog brug for yderligere undersøgelser for dokumentere dette

A study of the N2O emission from grassland with the FASSET farm model

Local adaptations of the IPCC methodology (http://www.ipcc.ch) are applied in different countries. They include a combination of theoretical, experimental and simulation methods for evaluating the activity and factors indicated N2O emission. The N2O emission from agricultural soil is considered an important source both for environmental impact and non-industrial losses of nitrogen (Petersen, Olesen, 2002). In this study a multifactorial approach, based on dynamic modelling, is used at a farm/field level to estimate N2O emission from grassland. For this purpose an algorithm for modeling of gaseous N2O emission was developed and analyzed. In the algorithm, based on the conceptual process-oriented model HIP (Davidson et al., 2000), both nitrification and denitrification are included as important sources for the N2O emission (Bremner, 1997). Soil-microbiological processes are described with first-order kinetics. The algorithm was implemented within the Danish farm model FASSET (Berntsen et al., 2003) to study of N2O emission from grassland under different treatments

Accessing topography-related spatial variability in crop yields using coupled agroecosystem-geomorphic modelling approach

A majority of the European arable fields is situated on rolling topographies, characterized by high in-field crop yields variability. In addition, geomorphic research has indicated that considerable within-field redistribution of soil material occurs. However, crop yield prognoses based on agroecosystem modelling typically characterize the soil system as static and as a point, i.e. as a single profile with generally unknown uncertainty. In order to improve the confidence levels for future agroecosystem development, it is essential to include this interaction between geomorphic and crop growth processes and to include uncertainty estimation while presenting the modelling results. We applied a spatially explicit approach in order to analyze relations between geomorphic processes, landscape position and crop growth. For this purpose, we use three computer experiments (“past”, assuming homogenous soil properties; “present”, time correspondent to the measured year; and “future”, in 50 years from “today” assuming the same soil redistribution rates) using downscaling technique. The approach was developed by implicit combination of the FASSET agroecosystem model, dynamically simulated crop growth dependent on meteorological and soil conditions, and the SPEROS geomorphic model, dynamically simulated lateral transfers of soil material and nutrients in the given landscape. To evaluate the approach, site-specific experimental data for croplands from two European locations (Belgium and the UK) were used, differing in climatic conditions, soil properties and management. Besides spatial difference in meteorological and initial soil properties in the fields, twofold water effect on soil-crop modelling system was considered: (1) effect related to differences in water retention as a result of differences in soil properties (e.g. texture, SOM), and (2) effect related to the topographical position. The results clearly show that soil redistribution significantly affected crop yields in all three computer experiments using the FASSET model. However, the model captured the observed effects in crop yields satisfactory only when both water effects were included in the simulations. Our simulations indicate that future landscape development as a result of ongoing soil redistribution will further increase spatial variability in crop yields. Furthermore, the results indicate higher crop variability and low potentials for reducing modelling uncertaintyforintensivelytilledscenariosinbothlocations.Finally,weshowhowthisapproachcanbedeveloped further as a tool for a long-term agroecosystem evolution analysis