Bioenergy crops are expected to provide biomass to replace fossil resources and reduce greenhouse gas emissions. In this context, changes in soil organic carbon (SOC) stocks are of primary ...importance. The aim of this study was to measure changes in SOC stocks in bioenergy cropping systems comparing perennial (Miscanthus × giganteus and switchgrass), semi‐perennial (fescue and alfalfa), and annual (sorghum and triticale) crops, all established after arable crops. The soil was sampled at the start of the experiment and 5 or 6 years later. SOC stocks were calculated at equivalent soil mass, and δ13C measurements were used to calculate changes in new and old SOC stocks. Crop residues found in soil at the time of SOC measurements represented 3.5–7.2 t C ha−1 under perennial crops vs. 0.1–0.6 t C ha−1 for the other crops. During the 5‐year period, SOC concentrations under perennial crops increased in the surface layer (0–5 cm) and slightly declined in the lower layers. Changes in δ13C showed that C inputs were mainly located in the 0–18 cm layer. In contrast, SOC concentrations increased over time under semi‐perennial crops throughout the old ploughed layer (ca. 0–33 cm). SOC stocks in the old ploughed layer increased significantly over time under semi‐perennials with a mean increase of 0.93 ± 0.28 t C ha−1 yr−1, whereas no change occurred under perennial or annual crops. New SOC accumulation was higher for semi‐perennial than for perennial crops (1.50 vs. 0.58 t C ha−1 yr−1, respectively), indicating that the SOC change was due to a variation in C input rather than a change in mineralization rate. Nitrogen fertilization rate had no significant effect on SOC stocks. This study highlights the interest of comparing SOC changes over time for various cropping systems.
Soil pH can be affected by land use change and acid deposition and is one of the primary regulators of nutrient cycling in the soil. In this study, two soils from adjacent forest and grassland sites ...in central Alberta were subjected to different pH treatments to evaluate the short-term effects of pH on soil gross N transformations using the 15N tracing technique and calculated by the numerical model FLUAZ. For the forest soil, gross NH4+ immobilization increased faster than gross N mineralization rates with increasing soil pH, leading to a declining pattern in net N mineralization rates; however, none of those rates changed with pH in the grassland soil. In contrast, the increase in pH significantly stimulated gross and net nitrification rates while soil acidification decreased gross and net nitrification rates for both the forest and grassland soils. The ratio of gross nitrification to gross NH4+ immobilization rates (N/IA) was significantly increased by KOH addition but declined to nearly zero by HCl addition for each soil. The low and high KCl addition treatments partially or completely inhibited gross nitrification rates, respectively, but gross mineralization was less sensitive to salt additions than the nitrification process. We conclude that based on the short-term laboratory incubation experiments both pH and salt (osmotic effect) affected gross N transformations and pH had contrasting effects on gross and net nitrogen mineralization but not on nitrification in the adjacent forest and grassland soils.
► Soil pH and salt effects on gross and net N transformations rates were studied in grassland and forests. ► Soil pH affected net and gross N mineralization in the two soils in different ways. ► Increasing pH increased gross and net nitrification rates in both soils. ► Salt reduced gross nitrification but not gross mineralization rates.
•40 years of full inversion, shallow or no-tillage lead to similar SOC stocks over the ploughed layer or down to 60cm.•In the reduced tillage treatments, SOC accumulated in the upper layer (0–10cm) ...but declined continuously below 10cm.•The amount of C sequestered due to reduced tillage followed a non-monotonic pattern over time.•Changes in SOC over time in the upper layer of no-till were negatively correlated with the water balance.•C sequestration rate was positive in dry periods and negative in wet conditions.
Although numerous studies have been conducted on the effect of tillage on soil organic carbon (SOC), there is still no consensus on the importance of sequestration which can be expected from reduced tillage. Most studies have used a synchronic approach in fields or long-term experiments which were often poorly characterized with respect to initial conditions. In this paper, we used a diachronic approach to quantify SOC changes in a 41 years experiment comparing no-till (NT), shallow till (ST) and full inversion tillage (FIT) combined with crop managements (residues removal, rotation and catch crops). It included SOC measurements at time 0 and every 4 years, calculations at equivalent soil mass within or below the old ploughed layer. Results show that tillage or crop management had no significant effect on SOC stocks after 41 years both in the old ploughed layer (ca. 0–28cm) and deeper (ca. 0–58cm). Tillage had no effect on crop yields and residues. In the reduced tillage treatments (ST and NT), SOC accumulated in the surface layer (0–10cm), reaching a plateau after 24 years but declined continuously in the lower layer (10–28cm) at a rate of 0.42–0.44% yr−1. The difference in SOC stocks (ST or NT minus FIT) over the old ploughed layer followed a non-monotonic pattern over time. Reduced tillage caused a rapid SOC sequestration during the first 4 years which remained more or less constant (mean=2.17 and 1.31tha−1, resp.) during the next 24 years and disappeared after 28 years. The drop was attributed to the higher water balance recorded during years 24–28. In the reduced tillage treatments, the changes in SOC over time were negatively correlated with the water balance, indicating that sequestration rate was positive in dry periods and negative in wet conditions. This study highlights the interest of diachronic approaches to understand the effect of tillage and its interaction with environmental and management factors.
Many studies have assessed the potential of agricultural practices to sequester carbon (C). A comprehensive evaluation of impacts of agricultural practices requires not only considering C storage but ...also direct and indirect emissions of greenhouse gases (GHG) and their side effects (e.g., on the water cycle or agricultural production). We used a high‐resolution modeling approach with the Simulateur mulTIdisciplinaire pour les Cultures Standard soil‐crop model to quantify soil organic C (SOC) storage potential, GHG balance, biomass production and nitrogen‐ and water‐related impacts for all arable land in France for current cropping systems (baseline scenario) and three mitigation scenarios: (i) spatial and temporal expansion of cover crops, (ii) spatial insertion and temporal extension of temporary grasslands (two sub‐scenarios) and (iii) improved recycling of organic resources as fertilizer. In the baseline scenario, SOC decreased slightly over 30 years in crop‐only rotations but increased significantly in crop/temporary grassland rotations. Results highlighted a strong trade‐off between the storage rate per unit area (kg C ha−1 year−1) of mitigation scenarios and the areas to which they could be applied. As a result, while the most promising scenario at the field scale was the insertion of temporary grassland (+466 kg C ha−1 year−1 stored to a depth of 0.3 m compared to the baseline, on 0.68 Mha), at the national scale, it was by far the expansion of cover crops (+131 kg C ha−1 year−1, on 17.62 Mha). Side effects on crop production, water irrigation and nitrogen emissions varied greatly depending on the scenario and production situation. At the national scale, combining the three mitigation scenarios could mitigate GHG emissions of current cropping systems by 54% (−11.2 from the current 20.5 Mt CO2e year−1), but the remaining emissions would still lie far from the objective of C‐neutral agriculture.
We used a high‐resolution modeling approach with the Simulateur mulTIdisciplinaire pour les Cultures Standard soil‐crop model to quantify soil organic carbon (C) storage potential, greenhouse gases (GHG) balance, biomass production and nitrogen‐ and water‐related impacts for all arable land in France for current cropping systems and three mitigation scenarios. At the national scale, combining the three mitigation scenarios could mitigate GHG emissions of current cropping systems by 54% (−11.2 from the current 20.5 Mt CO2e year−1), but the remaining emissions would still lie far from the objective of C‐neutral agriculture.
Sustainable bioenergy crops must contribute not only to the production of renewable energy but also to maintaining or restoring water resource and quality. The aim of this study was to quantify water ...drainage and nitrate leaching under perennial (
Miscanthus
×
giganteus
and switchgrass), “semi-perennial” (fescue and alfalfa) and annual (sorghum and triticale) bioenergy crops managed with two N fertilisation rates. Soil water and mineral N contents were measured twice a year during 7 consecutive years. These measurements were used to initialize the STICS model which simulated in turn the amounts of drained water and nitrate leached below 210 cm. Semi-perennial crops produced less drainage than annual crops (64 vs. 133 mm year
−1
) despite a similar biomass production. Perennial crops resulted in an intermediate drainage (90 mm year
−1
) but a greater biomass production. The drainage was negatively correlated with biomass production for perennial and annual crops. Perennial crops exhibited much higher water use efficiency than the other species. Nitrate concentration in drained water was low for all crops, most often less than 20 mg NO
3
l
−1
. It was lower for perennials than other crops, except for miscanthus on the first year of measurement. However, the comparison of model outputs with nitrate concentrations measured in subsoil after 5 years indicated that the peak of nitrate produced after miscanthus establishment was subsequently recovered by the crop in deep layers (below 210 cm). Perennial bioenergy crops have potential for restoring water quality but may decrease groundwater recharge in deep soils or dry climates.
Magnetic resonance imaging (MRI) has become an unrivalled medical diagnostic technique able to map tissue anatomy and physiology non-invasively. MRI measurements are meticulously engineered to ...control experimental conditions across the sample. However, residual radiofrequency (RF) field inhomogeneities are often unavoidable, leading to artefacts that degrade the diagnostic and scientific value of the images. Here we show that, paradoxically, these artefacts can be eliminated by deliberately interweaving freely varying heterogeneous RF fields into a magnetic resonance fingerprinting data-acquisition process. Observations made based on simulations are experimentally confirmed at 7 Tesla (T), and the clinical implications of this new paradigm are illustrated with in vivo measurements near an orthopaedic implant at 3T. These results show that it is possible to perform quantitative multiparametric imaging with heterogeneous RF fields, and to liberate MRI from the traditional struggle for control over the RF field uniformity.
The world's soils store more carbon than is present in biomass and in the atmosphere. Little is known, however, about the factors controlling the stability of soil organic carbon stocks and the ...response of the soil carbon pool to climate change remains uncertain. We investigated the stability of carbon in deep soil layers in one soil profile by combining physical and chemical characterization of organic carbon, soil incubations and radiocarbon dating. Here we show that the supply of fresh plant-derived carbon to the subsoil (0.6-0.8 m depth) stimulated the microbial mineralization of 2,567 226-year-old carbon. Our results support the previously suggested idea7 that in the absence of fresh organic carbon, an essential source of energy for soil microbes, the stability of organic carbon in deep soil layers is maintained. We propose that a lack of supply of fresh carbon may prevent the decomposition of the organic carbon pool in deep soil layers in response to future changes in temperature. Any change in land use and agricultural practice that increases the distribution of fresh carbon along the soil profile could however stimulate the loss of ancient buried carbon.
Repeated applications of organic amendments increase soil organic carbon (SOC) storage and nitrogen (N) availability for crops. Soil-crop models can facilitate the study of these effects and optimize ...the management of amendments. In soil-crop models, C and N mineralization of amendments is simulated by several pools of soil organic matter which have their specific turnover rate. We used the STICS model to quantify the effects of amendments on C and N dynamics in the long-term QualiAgro experiment, in which four amendments were spread every 2 years since 1998. We studied the model’s ability to simulate laboratory incubation and field experiments, depending on the calibration method and the partitioning of the amendment into one or two pools. The one-pool model simulated C and N dynamics in the field experiment as accurately as the two-pools model with a calibration based on field data. However, C and N dynamics measured under laboratory conditions could only be simulated with the two-pools model, which was then used to simulate C and N in the field. The root mean square errors were 1.6 t DM ha
−1
for grain yield, 2.6 t C ha
−1
for SOC and 41 kg N ha
−1
for soil mineral N. Model parameters could be determined using the C:N ratio of amendments and the indicator of remaining organic carbon (
I
ROC
), measured at the laboratory. The STICS model can thus be used to simulate SOC and N dynamics with long-term amendments with a simple calibration.
Agriculture is the main source of terrestrial N2O emissions, a potent greenhouse gas and the main cause of ozone depletion. The reduction of N2O into N2 by microorganisms carrying the nitrous oxide ...reductase gene (nosZ) is the only known biological process eliminating this greenhouse gas. Recent studies showed that a previously unknown clade of N2O‐reducers (nosZII) was related to the potential capacity of the soil to act as a N2O sink. However, little is known about how this group responds to different agricultural practices. Here, we investigated how N2O‐producers and N2O‐reducers were affected by agricultural practices across a range of cropping systems in order to evaluate the consequences for N2O emissions. The abundance of both ammonia‐oxidizers and denitrifiers was quantified by real‐time qPCR, and the diversity of nosZ clades was determined by 454 pyrosequencing. Denitrification and nitrification potential activities as well as in situ N2O emissions were also assessed. Overall, greatest differences in microbial activity, diversity, and abundance were observed between sites rather than between agricultural practices at each site. To better understand the contribution of abiotic and biotic factors to the in situ N2O emissions, we subdivided more than 59,000 field measurements into fractions from low to high rates. We found that the low N2O emission rates were mainly explained by variation in soil properties (up to 59%), while the high rates were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of the nosZII clade but not of the nosZI clade was important to explain the variation of in situ N2O emissions. Altogether, these results lay the foundation for a better understanding of the response of N2O‐reducing bacteria to agricultural practices and how it may ultimately affect N2O emissions.
We investigated how N2O‐producers and N2O‐reducers were affected by agricultural practices across a range of cropping systems and how peak and baseline N2O emissions were related to these microbial communities, We found that the low rates were mainly explained by variation in soil properties (up to 59%), while the high emissions were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of a recently discovered clade of N2O‐reducers (nosZII) was important to explain the variation of in situ N2O emission fractions. Altogether, these results lay the foundation for a better understanding of the response of N2O reducing bacteria to agricultural practices and how it may ultimately affect N2O emissions.
Purpose
To develop and test a deep learning approach named Convolutional Neural Network (CNN) for automated screening of T2‐weighted (T2WI) liver acquisitions for nondiagnostic images, and compare ...this automated approach to evaluation by two radiologists.
Materials and Methods
We evaluated 522 liver magnetic resonance imaging (MRI) exams performed at 1.5T and 3T at our institution between November 2014 and May 2016 for CNN training and validation. The CNN consisted of an input layer, convolutional layer, fully connected layer, and output layer. 351 T2WI were anonymized for training. Each case was annotated with a label of being diagnostic or nondiagnostic for detecting lesions and assessing liver morphology. Another independently collected 171 cases were sequestered for a blind test. These 171 T2WI were assessed independently by two radiologists and annotated as being diagnostic or nondiagnostic. These 171 T2WI were presented to the CNN algorithm and image quality (IQ) output of the algorithm was compared to that of two radiologists.
Results
There was concordance in IQ label between Reader 1 and CNN in 79% of cases and between Reader 2 and CNN in 73%. The sensitivity and the specificity of the CNN algorithm in identifying nondiagnostic IQ was 67% and 81% with respect to Reader 1 and 47% and 80% with respect to Reader 2. The negative predictive value of the algorithm for identifying nondiagnostic IQ was 94% and 86% (relative to Readers 1 and 2).
Conclusion
We demonstrate a CNN algorithm that yields a high negative predictive value when screening for nondiagnostic T2WI of the liver.
Level of Evidence: 2
Technical Efficacy: Stage 2
J. Magn. Reson. Imaging 2018;47:723–728.
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