Application of the DNDC model to predict N2O emissions from sandy arable soils with differing fertilization in a long‐term experiment

Modeling crop growth and soil N dynamics is difficult due to the complex nature of soil–plant systems. In several studies, the DNDC model has been claimed to be well‐suited for this purpose whereas in other studies applications of the model were less successful. Objectives of this study were to test a calibration and validation scheme for DNDC‐model applications to describe a field experiment with spring wheat on a sandy soil near Darmstadt (SW Germany) using different fertilizer types (either application of mineral fertilizer and straw—MSI; or application of farmyard manure—FYM) and rates (low—MSI_L, FYM_L; and medium—MSI_M, FYM_M). The model test is based on a model parameterization to best describe the case MSI_L and applies this parameterization for a retrospective simulation of the other cases (MSI_M, FYM_L, FYM_M) including crop growth and N₂O emissions. Soil water contents were not accurately simulated using either the DNDC default values for a loamy sand or for the next finer texture class or using results from the pedotransfer function provided by ROSETTA. After successful calibration of the soil water flow model using a soil texture class that led to the best fit of the measured water content data, grain yield of spring wheat and cumulative N₂O emission were slightly underestimated by DNDC and were between 91% and 86% of the measured data. A subsequent calibration of the yields and cumulative N₂O emissions from soils of the MSI_L treatment gave a good prediction of crop growth and N₂O emissions in the MSI_M treatment, but a marked underestimation of yields of the FYM treatments. Cumulative N₂O emissions were predicted well for all MSI and FYM treatments, but seasonal dynamics were not. Overall, our results indicated that for the sandy soil in Germany, site‐specific calibration was essentially required for the soil hydrology and that a calibration was useful for a subsequent prediction where greater amounts of the same fertilizer were used, but not useful for a prediction with a different fertilizer type.     

Features of follicular dendritic cells in ovine pharyngeal tonsil: an in vivo and in vitro study in the context of scrapie pathogenesis

Although the alimentary tract has been suggested as the most likely portal of entry in natural scrapie, a growing amount of data indicates that the respiratory system and more specifically the pharyngeal tonsils serve as a natural portal of entry for scrapie. This study describes for the first time the broad cell populations in the lymphoid compartment of pharyngeal tonsils and more specifically inside the lymphoid follicles where the scrapie agent accumulates during the period of latency. Follicular dendritic cells (FDCs), stromal cells located in the light zone of the germinal centre of lymphoid follicles, seem to be the principal causal factor in the accumulation of the infectious agent in transmissible spongiform encephalopathy (TSE) diseases. Knowing that efficient lymphoreticular prion propagation requires PrPc expression, we analysed the expression of PrPc with the mouse monoclonal antibody Pri 909 both in situ and on FDC-cluster-enriched cell suspensions. In situ, a positive staining was observed in the germinal centre of pharyngeal lymph follicles. The germinal centre labelling was due to the presence of a follicular dendritic network as revealed after immunogold staining of isolated FDC clusters. Our results suggest that the pharyngeal lymphoreticular system and more specifically PrPc expressing follicular dendritic cells could serve as a prion "reservoir" during the latency phase, thus playing a key role during the scrapie lymphoinvasion.     

Comparison of three methods for the detection of Potato virus Y in seed potato certification

Journal of Plant Diseases and Protection - Potato virus Y (PVY) is becoming increasingly important in potato growing regions worldwide. The main reason for this is an increase in the incidence of...     

Arbuscular Mycorrhizal Fungal Infectivity in Two Soils as Affected by Atmospheric Phenanthrene Pollution

Arbuscular mycorrhizal fungi (AMF) hold a crucial role in ecosystems because they are involved in nutrient cycling between soil and plants. This work aimed at evaluating the impacts that atmospheric pollution by polycyclic aromatic hydrocarbons may have on infectivity of indigenous AMF in soils. Two agricultural soils (Maconcourt, La Bouzule) were exposed for 2?weeks to ambient air (control, C) or to atmospheric phenanthrene (PHE) deposition (180???g?m^?3 air). After exposure, soils were divided into a top (0?C1?cm) and a bottom (1?C15?cm) layer fraction. AMF infectivities of soils were determined after 2?weeks of atmospheric exposition using leek (Allium porum) as bioassay plant. Atmospheric PHE was mainly recovered in the top layer of soil (500?C1,350???g?kg^?1) of both soils and did not readily diffuse into the depth. Atmospheric contamination led to decreases in AMF infectivities of the top layer in both soils and affected the growth of leeks. Our results not only report evidence that infectivity of indigenous AMF is sensitive to PHE in soils but also emphasize that AMF are primary affected by the soil layer regardless to the pollution level.     

Cause and duration of mustard incorporation effects on soil-borne plant pathogenic fungi

Two fungal plant pathogens, Rhizoctonia solani AG 2-2 and Fusarium oxysporum f.sp. lini, were studied in relation to general responses of soil fungi and bacteria following incorporation of Brassica juncea. Our aim was to understand to what extent the changes in the biological and physicochemical characteristics of the soil could explain the effects on the studied pathogens and diseases, and to determine the temporal nature of the responses. Short-term effects of mustard incorporation (up to 4 months) were investigated in a microcosm experiment, and compared with a treatment where composted plant material was incorporated. In a field experiment, the responses were followed up to 11 months after removal or incorporation of a mustard crop. In general, responses in the variables measured changed more after incorporation of fresh mustard material than after addition of similar amounts of composted plant material (microcosms) or after removal of the mustard crop (field). The soil inoculum potential of R. solani AG 2-2 decreased directly after incorporation of mustard, but increased later to disease levels above those in the untreated soil. Neither of these effects could be explained by changes in the population density of R. solani AG 2-2. Fusarium spp. were less influenced, although an increase in the suppressiveness to Fusarium wilt was observed after mustard incorporation as compared with the treatment where mustard was removed. The microbial responses to mustard incorporation were more pronounced for bacteria than for fungi. After an initial substantial increase, the bacterial density decreased but remained above the levels in the control treatment throughout the experimental periods. The bacterial community structure was modified up to 8 months after mustard incorporation. We conclude that incorporation of fresh mustard influences soil microbial communities, especially the bacteria, and has a potential to control the pathogenic activity of R. solani 2-2 on a short-term perspective. The time dependency in microbial responses is important and should be taken into consideration for the evaluation of the potential of Brassicas to control plant disease on a field scale.     

Adaptation of the STICS intercrop model to simulate crop growth and N accumulation in pea–barley intercrops

Cereal–legume intercrops are gaining increasing interest in Europe. Modelling, by taking into account the complexity of species interactions, can be a very useful tool to study such systems and to test new strategies in various soil and climatic conditions. The present work describes the adaptation of an intercrop model for pea–barley intercrops through the extrapolation of the STICS sole crop model and its parameterisation from experimental data recorded on sole crops. Several improvements have been added to the existing crop model to allow an inversion of dominance in height between species during the crop cycle and a trophic link between crop growth rate and the potential for N₂ fixation. A 2-year dataset on pea and barley sole crops grown under non-limiting water conditions and with full crop protection was first used for calibration. The intercrop model was subsequently tested on experimental datasets of pea–barley intercrops grown under the same conditions as the sole crops. The intercrop experiments used to test the intercrop model differed in soil type, soil N supply and plant densities of each species.     

Potential for microbial diuron mineralisation in a small wine‐growing watershed: from treated plots to lotic receiver hydrosystem

BACKGROUND: Since biological degradation processes are known to be a major driver of the natural attenuation of pesticide residues in the environment, microbial communities adapted to pesticide biodegradation are likely to play a key environmental role in reducing pesticide exposure in contaminated ecosystems. The aim of this study was to assess the diuron‐mineralising potential of microbial communities at a small‐scale watershed level, including a diuron‐treated vineyard (pollution source), its associated grass buffer strip (as a river protection area against pesticide runoff) and the lotic receiver hydrosystem (sediments and epilithon), by using radiorespirometry. RESULTS: Comparison of results obtained at different sampling sites (in both soil and aquatic systems) revealed the importance of diuron exposure in the adaptation of microbial communities to rapid diuron mineralisation in the vineyard but also in the contaminated grass strip and in downstream epilithic biofilms and sediments. CONCLUSION: This study provides strong suggestive evidence for high diuron biodegradation potential throughout its course, from the pollution source to the final receiving hydrosystem, and suggests that, after microbial adaptation, grass strips may represent an effective environmental tool for mineralisation and attenuation of intercepted pesticides. Copyright © 2009 Society of Chemical Industry     

Evaluating the transferability of measurements from simple constructed non weighable gravitation lysimeters to predict the water regime on field scale—a case study

The transfer of lysimeter‐based water balances to field scale is still a challenge, whereby the reliability of measured data from non‐weighable gravitation lysimeters (NWGL) is more questioned than the transferability of data from more modern lysimeter devices. The hypothesis of this study was to predict the water regime of a drained arable field (81 ha) based on measurement results of three neighboring (distance of 20 km northern Altmark region Saxony‐Anhalt, Germany) NWGL (surface area of 1 m², depth of 1.25 m) for three hydrological years (HY) from 11/1/2012 to 10/31/2015. For the first two HY, manually collected monthly outflow rates from the NWGL were comparable to registered (data logger) drain rates of the field. But NWGL outflow was underestimated as compared to field drainage in the third HY. This deficit in the lysimeter water balance was caused by heavy rain events in summer 2014 in combination with wind and interception by the crop canopy (Zea maize). Precipitation did not match the NWGL surface whereas this canopy effect did not play a role at the field site. Thus, further numerical simulations of the soil water flow with the HYDRUS 1D/2D‐software package, which were based only on input data determined at the NWGL (stand precipitation, potential evaporation/ transpiration) without taking into account the canopy effect, described registered outflow of the field adequately for the whole observation period. But determining precipitation matching the NWGL surface, which was not registered due to the missing weighing mechanism, is absolutely required to interpret deviating measured outflow rates.     

Negotiating a political path to agroforestry through the Conservation Security Program

Temperate agroforestry systems have faced obstacles to adoption despite their multiple environmental, economic, and social benefits. In part, these obstacles derive from the typically small scale of agroforestry systems relative to large-scale mainstream grain agriculture, which in the US is supported by strong commodity subsidies. One promising option for promoting agroforestry on a policy level, and thus for making it more appealing to landowners, is the Conservation Security Program (CSP), which provides payments to farmers for sustainable conservation practices on working lands. CSP was first passed in 2002 and has many supporters; however it has also faced opposition, delays in implementation and funding caps. CSP proponents have thus promoted its expansion in current and future Farm Bills. Since CSP is one part of the Farm Bill clearly suited to promoting agroforestry practices, supporters of agroforestry should consider joining coalitions around CSP to ensure that it includes explicit provisions for advancing agroforestry. In addition, CSP and agroforestry proponents alike should develop a strategic plan to market the expansion of CSP to policy makers. Specifically, a broad and strong coalition based on ideological common ground (e.g., attention to the notion of a family farmer) and on situational factors (e.g., potential international pressure from the World Trade Organization to reduce commodity subsidies) might be sufficient to push CSP into an expanded role in current and future Farm Bills.