Uwe Franko

A comparison of the performance of nine soil organic matter models using datasets from seven long-term experiments

Nine soil organic models were evaluated using twelve datasets from seven long-term experiments. Datasets represented three different land-uses (grassland, arable cropping and woodland) and a range of climatic conditions within the temperate region. Different treatments (inorganic fertilizer, organic manures and different rotations) at the same site allowed the effects of differing land management to be explored. Model simulations were evaluated against the measured data and the performance of the models was compared both qualitatively and quantitatively. Not all models were able to simulate all datasets; only four attempted all. No one model performed better than all others across all datasets. The performance of each model in simulating each dataset is discussed. A comparison of the overall performance of models across all datasets reveals that the model errors of one group of models (RothC, CANDY, DNDC, CENTURY, DAISY and NCSOIL) did not differ significantly from each other. Another group (SOMM, ITE and Verberne) did not differ significantly from each other but showed significantly larger model errors than did models in the first group. Possible reasons for differences in model performance are discussed in detail.

Simulation of temperature-, water- and nitrogen dynamics using the model CANDY

Abstract The theoretical basis of the simulation model CANDY (CArbon-Nitrogen-DYnamics) is briefly described along with results of its application to a test data set. The model contains modules for calculating soil temperature, moisture content and the processes of the soil carbon-nitrogen cycle. The model inputs are weather data (air temperature, precipitation and global radiation on a daily basis), plant development characteristics (seeding, harvesting, crop height and root depth), soil texture data and agricultural management (irrigation, fertilization, manuring, tillage). The test data material from two catchments in north Germany, one with loam soil (Neuenkirchen) and one with sand (Nienwohlde) included data from several nitrogen fertilizer treatments. The results show that the model outputs for temperature, moisture and nitrogen fit the observations quite well despite some deviations. Summarizing for all soil layers the square root of the mean quadratic differences of simulated and observed data are: for soil temperature ≤ 2.3 K for the loamy soil over a five-year period and ≤2.5 K for the sandy soil over a five-year period; for soil moisture ≤4.1 Vol.% for the loam and ≤4.4 Vol.% for the sand both over a three-year period. The results of soil nitrogen in 0–90 cm depth depend on the particular site under consideration. In most cases 2 3 of the whole data was contained within the deviation class less than or equal to 40 kg ha−1. The differences between observed and simulated data are within the usual range for applications on farm fields.

Impact of selected agricultural management options on the reduction of nitrogen loads in three representative meso scale catchments in Central Germany

Nitrogen inputs into surface waters from diffuse sources are still unduly high and the assessment of mitigation measures is associated with large uncertainties. The objective of this paper is to investigate selected agricultural management scenarios on nitrogen loads and to assess the impact of differing catchment characteristics in central Germany. A new modelling approach, which simulates spatially distributed N-transport and transformation processes in soil and groundwater, was applied to three meso scale catchments with strongly deviating climate, soil and topography conditions. The approach uses the integrated modelling framework JAMS to link an agro-ecosystem, a rainfall-runoff and a groundwater nitrogen transport model. Different agricultural management measures with deviating levels of acceptance were analysed in the three study catchments. N-leaching rates in all three catchments varied with soil type, the lowest leaching rates being obtained for loess soil catchment (18.5 kg nitrate N ha(-1) yr(-1)) and the highest for the sandy soils catchment (41.2 kg nitrate N ha(-1) yr(-1)). The simulated baseflow nitrogen concentrations varied between the catchments from 1 to 6 mg N l(-1), reflecting the nitrogen reduction capacity of the subsurfaces. The management scenarios showed that the highest N leaching reduction could be achieved by good site-adapted agricultural management options. Nitrogen retention in the subsurface did not alter the ranking of the management scenarios calculated as losses from the soil zone. The reduction effect depended strongly on site specific conditions, especially climate, soil variety and the regional formation of the crop rotations.

Modelling approaches of soil organic matter turnover within the CANDY system

The development of the CANDY system (CArbon and Nitrogen DYnamics) has been based on experience of organic matter turnover and nitrogen dynamics gained over a long period, a major part of the scientific work in Bad Lauchstadt. The main objective in developing the model was to give farmers a tool for calculating short term dynamics of nitrogen transformations and long term changes in the carbon content of the soil. For this reason the system consists of a database interface and several model components. The main component is the CANDY module, written in TURBO - PASCAL which calculates daily changes of water, temperature, carbon and nitrogen for a 2 m deep soil profile. Alongside this daily-timestep nitrogen simulation, there is a long term carbon module that calculates the amount of decomposable carbon in steady state for a given crop rotation. The calculation is specific to the site and management practices and is based on averaged turnover conditions, yields and inputs of organic material.

Modellierung des umsatzes der organischen bodensubstanz

Modelle zum Umsatz der organischen Bodensubstanz (OBS) werden seit langer Zeit entwickelt. Die Ergebnisse aus Dauerversuchen zeigen, das mindestens zwei OBS Fraktionen (inert und umsetzbar) existieren. Weitergehende Untersuchungen fuhrten zur Definition einer aktiven und einer stabilisierten Fraktion innerhalb der umsetzbaren OBS. Einfache Modelle arbeiten in Jahresschritten, was zu einer geometrischen Reihe fuhrt. Die Losung von Differentialgleichungen bietet bessere Moglichkeiten zur Beschreibung der Umsatzdynamik mit beliebiger Zeitauflosung. Die Besonderheit des hier beschriebenen Modells besteht im Ausdruck der Umweltwirkungen als Zeittransformation und in der Berechnung des reproduktionswirksamen Kohlenstoffinputs. Ein Rechenschema, erganzt durch die erforderlichen Parameter verdeutlicht, wie das standortspezifische Niveau der umsetzbaren OBS zu ermitteln ist. Die Stickstoffdynamik ist eng mit dem Kohlenstoffumsatz verbunden. Mineralisierung und Immobilisierung ergeben sich aus den C/N‐Verhaltnissen...

EuroSOMNET – a European database of long-term experiments on soil organic matter: the WWW metadatabase

Since 1997, the EuroSOMNET project, funded by the EU-ENRICH programme, has assembled a metadatabase, and separate experimental databases, of European long-term experiments that investigate changes in soil organic matter. In this paper, we describe the WWW-based metadatabase, which is a product of this project. The database holds detailed records of 110 long-term soil organic matter experiments, giving a wide geographical coverage of Europe, and includes experiments from the European part of the former Soviet Union, many of which have not been available previously. For speed of access, records are stored as hyper-text mark-up language (HTML) files. In this paper, we describe the metadatabase, the experiments for which records are held, the information stored about each experiment, and summarize the main characteristics of these experiments. Details from the metadatabase have already been used to examine regional trends in soil organic matter in Germany and eastern Europe, to construct and calibrate a regional statistical model of humus balance in Russia, to examine the effects of climatic conditions on soil organic matter dynamics, to estimate the potential for carbon sequestration in agricultural soils in Europe, and to test and improve soil organic matter models. The EuroSOMNET metadatabase provides information applicable to a wide range of agricultural and environmental questions and can be accessed freely via the EuroSOMNET home page at URL: http://www.iacr.bbsrc.ac.uk/aen/eusomnet/index.htm.

Spatially Distributed Lateral Nitrate Transport at the Catchment Scale

In river catchments, N transformation and storage processes during lateral transport are important in controlling N loads of surface waters. There is a lack of approaches which capture lateral flows and associated N transformation in a spatially distributed way. The aim of this paper is to develop a new conceptual N transport and transformation model which simulates the lateral nitrate transport in subsurface flow from the source area to the receiving water body. The developed tool is based on the object modeling system (OMS) framework and consists of the analytical spatially distributed hydrological model J2000, the nitrate recharge model Meta Candy and a new groundwater N routing component. Nitrate degradation in groundwater is calculated stoichiometrically according to a predefined amount on oxidizable substrate. The new modeling approach was tested in a small agricultural lower mountain range catchment of Thuringia, Germany. The calibration of the N model using a 4-yr period showed reasonable results for nitrate load calculations with a Nash and Sutcliff coefficient of 0.78. The 3-yr validation period produced Nash-Sutcliff (NS) values of 0.75. There was a clear relationship of the goodness-of-fit between the hydrological simulations and the nitrate concentration calculations. Due to short residence times of the interflow nitrate degradation was restricted to slow base flow components. The new approach can be used to target N source areas within a catchment and assess the impact of these source areas on the N load of surface waters in a spatially distributed manner.

Einfluss von klima und textur auf die biologische aktivität beim umsatz der organischen bodensubstanz

Der Umsatz organischer Bodensubstanzen last sich durch Kinetiken 1. Ordnung beschreiben. Die Reaktionskoeffizienten sind von der Bodentemperatur und ‐feuchte sowie den Aerationsverhaltnissen im Boden abhangig. Unter Verwendung des Quasistationaritatsprinzips konnen die Umsatzprozesse in einer biologischen Zeitbasis, der wirksamen Mineralisierungszeit (WMZ), auf einfache und uberschaubare Art und Weise beschrieben werden. Die standortspezifischen Werte der WMZ mussen in der Regel durch zeitaufwendige Simulationsrechnungen uber verschiedene Fruchtfolgen ermittelt werden. Zur Vereinfachung wurde eine Regressionsgleichung entwickelt, mit deren Hilfe eine Abschatzung der standorttypischen Jahressumme der WMZ bei Kenntnis des Jahresmittels der Lufttemperatur, des Niederschlags sowie des Feinanteilgehaltes im Boden moglich ist.

EuroSOMNET—a database for long-term experiments on soil organic matter in Europe

Abstract Long-term experiments are usually connected with a large volume of data published in many different papers. Centralised storage of information in the form of databases is a suitable way to make the data more accessible for possible users. Although a collection of metadata exists on long-term experiments in Europe, related to the turnover of soil organic matter, a convenient method to access the actual data was required. The EuroSOMNET database has been designed in order to save detailed information from those experiments. The data model contains five pools of information: basics, climate, soil information, field management and results. Dataholders decide on the state of accessibility of their dataset (related to each experiment). Possible states range from private (access only for dataholders) to public (access to all Internet users). The most important advantages of this system are a standardised yet flexible data structure that facilitates the data exchange between different users. At this time there are 25 experiments at different states of data processing stored. The sites extend from Russia to Great Britain. Land use systems contained are arable systems, grassland, bare fallow and vegetable production.

Die organische bodensubstanz —bedeutung, definition, bestimmung

Die organische Substanz des Bodens (OBS) ist Voraussetzung fur Bodenbildung und Bodenfunktionen. Es werden die Vielfalt der gebrauchlichen Definitionen dargestellt und die Probleme einer ausreichend genauen Bestimmung diskutiert. Eine direkte Bestimmung ist praktisch nicht moglich. Fur den Kohlenstoffgehalt der OBS werden in der Literatur Faktoren zwischen 1,6 und 3,3 angegeben. Der Corg‐Gehalt im Boden hat eine grose zeitliche und raumliche Variabilitat, die Einhaltung der zu fordernden Prazision und Treffgenauigkeit wird zusatzlich durch die verschiedenen Bestimmungsmethoden und ihren zahllosen apparativen und methodischen Variationen erschwert. Fur eine Bewertung der OBS ist eine Differenzierung nach dem Grad ihrer Umsetzbarkeit erforderlich. Es wird eine entsprechende Gliederung der OBS als Voraussetzung fur die Modellierung von Umsetzungsprozessen vorgeschlagen.