Functional Multi-Scale Integration of Agricultural Nitrogen-Budgets Into Catchment Water Quality Modeling

Funding Information: The work is supported by the TERENO and MOSES projects, Helmholtz Association. The authors highly acknowledge the data from the Extended Static Fertilization Experiment at Bad Lauchst?dt and the State Institute for Agriculture and Horticulture Saxony-Anhalt. The authors also thank the German Weather Service, the Federal Institute for Geosciences and Natural Resources and the State Agency for Flood Protection and Water Management Saxony-Anhalt for the model setup data. The authors thank the Editor Harihar Rajaram and two anonymous reviewers for their constructive comments. Open access funding enabled and organized by Projekt DEAL.Peer reviewedPublisher PD

Simulating the soil phosphorus dynamics of four long‐term field experiments with a novel phosphorus model

Phosphorus is a nonrenewable resource, which is required for crop growth and to maintain high yields. The soil P cycle is very complex, and new model approaches can lead to a better understanding of those processes and further guide to research gaps. The objective of this study was to present a P-submodel, which has been integrated in the existing Carbon Candy Balance (CCB) model that already comprises a C and N module. The P-module is linked to the C mineralization and the associated C-pools via the C/P ratio of fresh organic material. Besides the organic P cycling, the module implies a plant-available P-pool (Pav), which is in a dynamic equilibrium with the nonavailable P-pool (Pna) that comprises the strongly sorbed and occluded P fraction. The model performance was tested and evaluated on four long-term field experiments with mineral P fertilization, farmyard manure as organic fertilizer and control plots without fertilization. The C dynamics and the Pav dynamics were modelled with overall good results. The relative RMSE for the C was below 10% for all treatments, while the relative RMSE for Pav was below 15% for most treatments. To accommodate for the rather small variety of available P-models, the presented CNP-model is designed for agricultural field sites with a relatively low data input, namely air temperature, precipitation, soil properties, yields and management practices. The CNP-model offers a low entry threshold model approach to predict the C-N and now the P dynamics of agricultural soils.Fachagentur Nachwachsende Rohstoffe http://dx.doi.org/10.13039/501100010812Peer Reviewe

Differences in labile soil organic matter explain potential denitrification and denitrifying communities in a long-term fertilization experiment

Content and quality of organic matter (OM) may strongly affect the denitrification potential of soils. In particular, the impact of soil OM fractions of differing bioavailability (soluble, particulate, and mineral-associated OM) on denitrification remains unresolved. We determined the potential N2O and N2 as well as CO2 production for samples of a Haplic Chernozem from six treatment plots (control, mineral N and NP, farmyard manure - FYM, and FYM + mineral N or NP) of the Static Fertilization Experiment Bad Lauchstädt (Germany) as related to OM properties and denitrifier gene abundances. Soil OM was analyzed for bulk chemical composition (13C-CPMAS NMR spectroscopy) as well as water-extractable, particulate, and mineral-associated fractions. Soils receiving FYM had more total OM and larger portions of labile fractions such as particulate and water-extractable OM. Incubations were run under anoxic conditions without nitrate limitation for seven days at 25 °C in the dark to determine the denitrification potential (N2O and N2) using the acetylene inhibition technique. Abundances of nirS, nirK, and nosZ (I + II) genes were analyzed before and after incubation. The denitrification potential, defined as the combined amount of N released as N2O + N2 over the experimental period, was larger for plots receiving FYM (25.9–27.2 mg N kg−1) than pure mineral fertilization (17.1–19.2 mg N kg−1) or no fertilization (12.6 mg N kg−1). The CO2 and N2O production were well related and up to three-fold larger for FYM-receiving soils than under pure mineral fertilization. The N2 production differed significantly only between all manured and non-manured soils. Nitrogenous gas emissions related most closely to water-extractable organic carbon (WEOC), which again related well to free particulate OM. The larger contribution of N2 production in soils without FYM application, and thus, with less readily decomposable OM, coincided with decreasing abundances of nirS genes (NO2− reductase) and increasing abundances of genes indicating complete denitrifying organisms (nosZ I) during anoxic conditions. Limited OM sources, thus, favored a microbial community more efficient in resource use. This study suggests that WEOC, representing readily bioavailable OM, is a straightforward indicator of the denitrification potential of soils

Response of subsoil organic matter contents and physical properties to long‐term, high‐rate farmyard manure application

Application of farmyard manure (FYM) is common practice to improve physical and chemical properties of arable soil and crop yields. However, studies on effects of FYM application mainly focussed on topsoils, whereas subsoils have rarely been addressed so far. We, therefore, investigated the effects of 36‐year FYM application with different rates of annual organic carbon (OC) addition (0, 469, 938 and 1875 g C m−2 a−1) on OC contents of a Chernozem in 0–30 cm (topsoil) and 35–45 cm (subsoil) depth. We also investigated its effects on soil structure and hydraulic properties in subsoil. X‐ray computed tomography was used to analyse the response of the subsoil macropore system (≥19 μm) and the distribution of particulate organic matter (POM) to different FYM applications, which were related to contents in total OC (TOC) and water‐extractable OC (WEOC). We show that FYM‐C application of 469 g C m−2 a−1 caused increases in TOC and WEOC contents only in the topsoil, whereas rates of ≥938 g C m−2 a−1 were necessary for TOC enrichment also in the subsoil. At this depth, the subdivision of TOC into different OC sources shows that most of the increase was due to fresh POM, likely by the stimulation of root growth and bioturbation. The increase in subsoil TOC went along with increases in macroporosity and macropore connectivity. We neither observed increases in plant‐available water capacity nor in unsaturated hydraulic conductivity. In conclusion, only very high application of FYM over long periods can increase OC content of subsoil at our study site, but this increase is largely based on fresh, easily degradable POM and likely accompanied by high C losses when considering the discrepancy between OC addition rate by FYM and TOC response in soil. Highlights A new image processing procedure to distinguish fresh and decomposed POM. The increase of subsoil C stock based to a large extend on fresh, labile POM. Potential of arable subsoils for long‐term C storage by large FYM application rates is limited. The increase in TOC has no effect on hydraulic properties of the subsoil.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

Simulating the soil phosphorus dynamics of four long‐term field experiments with a novel phosphorus model

Phosphorus is a nonrenewable resource, which is required for crop growth and to maintain high yields. The soil P cycle is very complex, and new model approaches can lead to a better understanding of those processes and further guide to research gaps. The objective of this study was to present a P‐submodel, which has been integrated in the existing Carbon Candy Balance (CCB) model that already comprises a C and N module. The P‐module is linked to the C mineralization and the associated C‐pools via the C/P ratio of fresh organic material. Besides the organic P cycling, the module implies a plant‐available P‐pool (Pav), which is in a dynamic equilibrium with the nonavailable P‐pool (Pna) that comprises the strongly sorbed and occluded P fraction. The model performance was tested and evaluated on four long‐term field experiments with mineral P fertilization, farmyard manure as organic fertilizer and control plots without fertilization. The C dynamics and the Pav dynamics were modelled with overall good results. The relative RMSE for the C was below 10% for all treatments, while the relative RMSE for Pav was below 15% for most treatments. To accommodate for the rather small variety of available P‐models, the presented CNP‐model is designed for agricultural field sites with a relatively low data input, namely air temperature, precipitation, soil properties, yields and management practices. The CNP‐model offers a low entry threshold model approach to predict the C‐N and now the P dynamics of agricultural soils.Fachagentur Nachwachsende Rohstoffe http://dx.doi.org/10.13039/50110001081

Meteorological data (1997-2018) of experimental field station in Bad Lauchstädt, Germany

The considered data set contains measurements of 4 automatic weather stations from 1997 until 2018 installed by Helmholtz Centre for Environmental Research - UFZ GmbH. Here, the main station corresponded to typical sensor technology and equipment of the German Meteorological Service [Deutscher Wetterdienst, DWD]. These data were quality-checked and processed as daily values. As far as possible, erroneous values were replaced by means of other stations on site. Very short failures could be supplemented by interpolation or averaging. Hence, values of measured variable can originate from different stations. However, only one value for each measured variable is provided for every day within the table. A unique label for individual weather stations is used to identify the exact origin of data

Meteorological data of experimental field station in Bad Lauchstädt, Germany

Continuously measured weather data are of utmost importance for ecological and environmental field experiments in Bad Lauchstädt, Germany. For this reason, data were collected from different sources: i) handwritten records from weather stations at the experimental sites, ii) records from meteorological service of German Democratic Republic and iii), German Meteorological Service [Deutscher Wetterdienst, DWD]. The DWD had digitalized handwritten data before their recording started in 1991 and was therefore able to publish data going back to 1947. Historical data before 1947 are not yet published. Thus, starting in 2007 until 2018, the DWD did not operate their own weather station on site. The data of this publication intend to complete the time periods before 1947 and between 2007 and 2018 in a long-term data series. Our complete available data sets of extent weather information on site (1896-1955; 1997-2018) are presented additionally

Historical meteorological data (1896 – 1955) of experimental field station in Bad Lauchstädt, Germany

The historical weather data from 1896 to 1955 complete the long-term series of measurements of the weather data of Bad Lauchstädt. Values are available for air temperature and precipitation as pentad values (sum values of 5 days). Unfortunately, the exact origin of the data, as well as the measurement method and the quality of the data cannot be described. The data were digitalized on basis of original records of the experimental station and documents of the Central Office of the German Meteorological Service [Deutscher Wetterdienst] (see reference Hoffmann et al.). The data were checked for plausibility, but a residual uncertainty still remains. Nevertheless, the data represent an important contribution to a complete weather description at the site of Bad Lauchstädt. With the help of these data, evaluations and modelling of long-term experiments are possible

Imagine All the Plants: Evaluation of a Light-Field Camera for On-Site Crop Growth Monitoring

The desire to obtain a better understanding of ecosystems and process dynamics in nature accentuates the need for observing these processes in higher temporal and spatial resolutions. Linked to this, the measurement of changes in the external structure and phytomorphology of plants is of particular interest. In the fields of environmental research and agriculture, an inexpensive and field-applicable on-site imaging technique to derive three-dimensional information about plants and vegetation would represent a considerable improvement upon existing monitoring strategies. This is particularly true for the monitoring of plant growth dynamics, due to the often cited lack of morphological information. To this end, an innovative low-cost light-field camera, the Lytro LF (Light-Field), was evaluated in a long-term field experiment. The experiment showed that the camera is suitable for monitoring plant growth dynamics and plant traits while being immune to ambient conditions. This represents a decisive contribution for a variety of monitoring and modeling applications, as well as for the validation of remote sensing data. This strongly confirms and endorses the assumption that the light-field camera presented in this study has the potential to be a light-weight and easy to use measurement tool for on-site environmental monitoring and remote sensing purposes