Rotational History Research Articles

Crop rotational complexity affects plant-soil nitrogen cycling during water deficit

One of the biggest environmental challenges facing agriculture is how to both supply and retain nitrogen (N), especially as precipitation becomes more variable with climate change. We used a greenhouse experiment to assess how contrasting histories of crop rotational complexity affect plant-soil-microbe interactions that govern N processes, including during water stress. With higher levels of carbon and N cycling hydrolytic enzymes, higher mineral-associated organic matter N concentrations, and an altered microbial community, soils from the most complex rotation enabled 80% more corn N uptake under two moisture regimes, compared to soil from monoculture corn. Higher levels of plant N likely drove the changes in corn leaf gas exchange, particularly increasing intrinsic water use efficiency by 9% in the most complex rotation. The water deficit increased the standing pool of nitrate 44-fold in soils with a history of complex crop rotations, compared to an 11-fold increase in soils from the corn monoculture. The implications of this difference must be considered in a whole cropping systems and field context. Cycling of 15N-labeled fresh clover residue into soil N pools did not depend on the water regime or rotation history, with 2-fold higher recovery in the mineral vs. particulate organic N pool. In contrast, the water deficit reduced recovery of clover 15N in corn shoots by 37%, showing greater impacts of water deficit on plant N uptake compared to organic N cycling in soil. This study provides direct experimental evidence that long-term crop rotational complexity influences microbial N cycling and availability with feedbacks to plant physiology. Collectively, these results could help explain general observations of higher yields in more complex crop rotations, including specifically during dry conditions.

Monte Carlo simulations of evolving rotational distributions of low-mass stars in young open clusters. Testing the influence of initial conditions

ABSTRACT The rotational evolution of a young stellar population can give informations about the rotation pattern of more evolved clusters. Combined with rotational period values of thousands of young stars and theoretical propositions about the redistribution and loss of stellar angular momentum, it allows us to trace the rotational history of stars according to their mass. We want to investigate how internal and environmental changes on single stars can change the rotational evolution of a young stellar population. We run Monte Carlo simulations of a young cluster composed by solar mass stars of 0.5, 0.8 and 1.0 M⊙ from 1 to 550 Myr taking into account observational and theoretical parameters. In order to compare our results with the observations we run Kolmogorov-Smirnov tests. Our standard model is able to reproduce some clusters younger than h Per and marginally M37, which is 550 Myr old. Varying the disk fraction or the initial period distribution did not improve the results. However, when we run a model with a finer mass grid the Pleiades can be also reproduced. Changing the initial mass distribution to be similar to the empirical ONC mass function also gives good results. Modeling the evolution of a young synthetic cluster from pre-main sequence to early main sequence considering physical mechanisms of extraction and exchange of angular momentum can not be achieved successfully for all clusters for which we have enough rotational data. Clusters of about the same age present different rotational behaviors due perhaps to differences in their initial conditions.

The influence of the environment on the spin evolution of low-mass stars – I. External photoevaporation of circumstellar discs

ABSTRACT Massive stars are strong sources of far-ultraviolet radiation that can be hostile to the evolution of protoplanetary discs, driving mass-loss by external photoevaporation and shortening disc-dissipation time-scales. Their effect may also reduce the time-scale of angular momentum exchanges between the disc and host star during the early pre-main-sequence phase. To improve our understanding of the environmental influence on the rotational history of stars, we developed a model that considers the influence of the local far-ultraviolet radiation on the spin evolution of low mass stars. Our model includes an assumption of disc locking, which fixes the rotation rate during the star-disc-interaction phase, with the duration of this phase parametrized as a function of the local far-ultraviolet radiation and stellar mass (in the range of 0.1–1.3 M⊙). In this way, we demonstrate how the feedback from massive stars can significantly influence the spin evolution of stars and explain the mass dependence observed in period-mass distributions of young regions like Upper Sco and NGC 2264. The high far-ultraviolet environments of high-mass stars can skew the period distribution of surrounding stars towards fast-rotation, explaining the excess of fast-rotating stars in the open cluster h Per. The proposed link between rotation and the pre-main-sequence environment opens new avenues for interpreting the rotational distributions of young stars. For example, we suggest that stellar rotation may be used as a tracer for the primordial ultraviolet irradiation for stars up to ∼1 Gyr, which offers a potential method to connect mature planetary systems to their birth environment.

The key impact of the host star’s rotational history on the evolution of TOI-849b

Context. TOI-849b is one of the few planets populating the hot-Neptune desert and it is the densest Neptune-sized one discovered so far. Its extraordinary proximity to the host star, together with the absence of a massive H/He envelope on top of the 40.8 M⊕ rocky core, calls into question the role played by the host star in the evolution of the system. Aims. We aim to study the impact of the host star’s rotational history on the evolution of TOI-849b, particularly focussing on the planetary migration due to dynamical tides dissipated in the stellar convective envelope, and on the high-energy stellar emission. Methods. Rotating stellar models of TOI-849 are coupled to our orbital evolution code to study the evolution of the planetary orbit. The evolution of the planetary atmosphere is studied by means of the JADE code, which uses realistic X-ray and extreme-ultraviolet (XUV) fluxes provided by our rotating stellar models. Results. Assuming that the planet was at its present-day position (ain = 0.01598 AU) at the protoplanetary disc dispersal, with mass 40.8 M⊕, and considering a broad range of host star initial surface rotation rates (Ωin ∈ [3.2, 18] Ω⊙), we find that only for Ωin ≤ 5 Ω⊙ do we reproduce the current position of the planet, given that for Ωin > 5 Ω⊙ its orbit is efficiently deflected by dynamical tides within the first ∼40 Myr of evolution. We also simulated the evolution of the orbit for values of ain ≠ 0.01598 AU for each of the considered rotational histories, confirming that the only combination suited to reproduce the current position of the planet is given by ain = 0.01598 AU and Ωin ≤ 5 Ω⊙. We tested the impact of increasing the initial mass of the planet on the efficiency of tides, finding that a higher initial mass (Min = 1 MJup) does not change the results reported above. Based on these results we computed the evolution of the planetary atmospheres with the JADE code for a large range of initial masses above a core mass of 40.8 M⊕, finding that the strong XUV-flux received by the planet is able to remove the entirety of the envelope within the first 50 Myr, even if it formed as a Jupiter-mass planet.

Pre- and within-season crop type classification trained with archival land cover information

Crop type maps were created without the traditional need for in-season training data across the Corn Belt and Great Plains regions of the United States. This was accomplished through machine learning of historical land cover information, paired with a time-series of multi-spectral satellite imagery composites spanning the growing season, to develop rulesets, which were used for real-time prediction in the current year. Specifically, a decade's worth of annual 30 m resolution crop specific maps, known as the Cropland Data Layer (CDL), provided the foundation, and prior and current year's satellite imagery from Landsat 7 and 8 and Sentinel-2a and -2b built upon it. Four modeling scenarios, all using random forests, were performed to understand the crop mapping abilities of the datasets independently and combined. They were 1) use of CDLs only (i.e. prediction based solely on crop rotation history) 2) use of Landsat 7 and 8 bottom-of-atmosphere surface reflectance imagery only, 3) use of Sentinel-2a and -2b top-of-atmosphere imagery only, and 4) integration of the CDL, Landsat, and Sentinel-2 information together in a unified effort. Furthermore, the model runs were generated monthly, beginning in April, through the growing season to provide understanding of classification performance as a function of time. The 2020 crop year, relatively normal in terms of planting and weather, was used for the test. Accuracy statistics were generated by randomly sampling 50 counties and comparing those classification outputs to the actual 2020 CDL. Pixel-level results showed that prediction by midsummer using only the CDL information provided a crop type map with corn and soybean consumer and producer agreement above 70% and winter wheat just below 50%. The early season imagery-based classifications were markedly worse. However, as Landsat or Sentinel-2 imagery accumulated through July, those classifications became significantly better than those reliant on the use of the CDL information only. Ultimately, the very best crop maps resulted from integrating the CDLs with a full season's worth of Landsat and Sentinel-2 imagery. At that point in late September, the corn and soybean agreements were around 85% and winter wheat near 70%. All analysis was performed within Google Earth Engine cloud-based public imagery repository and high-performance computing system. The classification outputs provide practitioners with US crop type maps in near real-time.

Legacy effects of pre-crop plant functional group on fungal root symbionts of barley.

Arbuscular mycorrhizal (AM) fungi, a group of widespread fungal symbionts of crops, could be important in driving crop yield across crop rotations through plant-soil feedbacks (PSF). However, whether preceding crops have a legacy effect on the AM fungi of the subsequent crop is poorly known. We set up an outdoor mesocosm crop rotation experiment that consisted of a first phase growing either one of four pre-crops establishing AM and/or rhizobial symbiosis or not (spring barley, faba bean, lupine, canola), followed by an AM crop, winter barley. After the pre-crop harvest, carbon-rich organic substrates were applied to test whether it attenuated, accentuated or modified the effect of pre-crops. The pre-crop mycorrhizal status, but not its rhizobial status, affected the richness and composition of AM fungi, and this difference, in particular community composition, persisted and increased in the roots of winter barley. The effect of a pre-crop was driven by its single symbiotic group, not its mixed symbiotic group and/or by a crop-species-specific effect. This demonstrates that the pre-crop symbiotic group has lasting legacy effects on the AM fungal communities and may steer the AM fungal community succession across rotation phases. This effect was accentuated by sawdust amendment, but not wheat straw. Based on the previous observation of decreased crop yield after AM pre-crops, our findings suggest negative PSF at the level of the plant symbiotic group driven by a legacy effect of crop rotation history on AM fungal communities, and that a focus on crop symbiotic group offers additional understanding of PSF.

Crop rotation history constrains soil biodiversity and multifunctionality relationships

Human agricultural activities are recognized to play a major role in structuring soil microbial communities, which are of critical importance in terms of maintaining the multiple functions of soil (‘multifunctionality’ hereafter). However, the impact of agricultural management history on soil multifunctionality and its relationship with soil microbial diversity has not been well understood enough. To address this gap, we characterized the multifunctionality (via activity of multiple extracellular enzymes) in soils subjected to four rice rotation regimes (rice-rapeseed, rice-wheat, rice-vegetable and rice-fallow) with or without fertilization and explored the linkages between bacterial community diversity and soil multifunctionality. We found that the crop rotation history rather than fertilization explained a significant portion of the variation in soil multifunctionality (52%), bacterial species richness (69%) and community composition (61%). Bacterial diversity (species richness and weighted Unifrac dissimilarity) exhibited strong positive relationships with soil multifunctionality. In particular, bacterial diversity in the rice-rapeseed rotation had the strongest effect on the ability of the soil system to provide more functions. Partial least squares path modeling indicated that crop rotation indirectly controlled soil multifunctionality via changes in bacterial species richness and community composition, which positively affected multifunctionality mainly by regulating C cycling-related enzyme activities. This study highlights the importance of the crop rotation history in influencing soil microbial diversity and multifunctionality relationships, indicating rice rotation with rapeseed combined with fertilization can greatly improve soil multifunctionality despite the typical focus on nutrient inputs in cropland ecosystems.

Revisiting Kepler-444

Context.Kepler-444 is one of the oldest planetary systems known thus far. Its peculiar configuration consisting of five sub-Earth-sized planets orbiting the companion to a binary stellar system makes its early history puzzling. Moreover, observations of HI-Lyαvariations raise many questions about the potential presence of escaping atmospheres today.Aims.We aim to study the orbital evolution of Kepler-444-d and Kepler-444-e and the impact of atmospheric evaporation on Kepler-444-e.Methods.Rotating stellar models of Kepler-444-A were computed with the Geneva stellar evolution code and coupled to an orbital evolution code, accounting for the effects of dynamical, equilibrium tides and atmospheric evaporation. The impacts of multiple stellar rotational histories and X-ray and extreme ultraviolet (XUV) luminosity evolutionary tracks are explored.Results.Using detailed rotating stellar models able to reproduce the rotation rate of Kepler-444-A, we find that its observed rotation rate is perfectly in line with what is expected for this old K0-type star, indicating that there is no reason for it to be exceptionally active as would be required to explain the observed HI-Lyαvariations from a stellar origin. We show that given the low planetary mass (~0.03 M⊕) and relatively large orbital distance (~0.06 AU) of Kepler-444-d and e, dynamical tides negligibly affect their orbits, regardless of the stellar rotational history considered. We point out instead how remarkable the impact is of the stellar rotational history on the estimation of the lifetime mass loss for Kepler-444-e. We show that, even in the case of an extremely slow rotating star, it seems unlikely that such a planet could retain a fraction of the initial water-ice content if we assume that it formed with a Ganymede-like composition.

Rotational states and shapes of Ryugu and Bennu: Implications for interior structure and strength

Images of asteroids (162173) Ryugu and (101955) Bennu acquired by the Hayabusa2 and OSIRIS-REx missions, respectively, reveal rocky worlds covered in rubble. These two asteroids do not have hydrostatic shapes, indicating that they possess some internal friction and/or cohesion even if they lack tensile strength. Understanding the deviation of the surfaces of these bodies from those of idealized shapes helps constrain the mechanical properties of their interiors. Here, we focus on the feedback between YORP-induced spin-up (in which asymmetric reflection and re-emission of solar radiation from the surface systematically change the rotation rate), long-wavelength topography (which provides a structure to control the orientation), and surface roughness on Ryugu and Bennu. By performing spherical harmonic analyses of the shapes of these two asteroids, we find that although they are superficially similar, they exhibit different long-wavelength topography that implies different internal structures and rotational histories. Bennu's shape and rotation rate require a modest amount of internal strength through some combination of at least 17° of internal friction or a few Pa of cohesion, whereas Ryugu could be nearly strengthless. Bennu's longitudinal ridges make it susceptible to YORP spin-up, consistent with the observed increase in rotation rate that is not seen on Ryugu. These longitudinal ridges also suggest a heterogeneous density structure for Bennu, consistent with gravity data.

Experimental characterization of a novel nose landing gear shimmy damper using a small-scale test rig

This paper presents the design and fabrication details of a small-scale testing system for characterizing a novel nose landing gear shimmy damper. This test rig is designed to simulate take-off and landing conditions of an aircraft nose landing gear in the laboratory environment. A roller drum is employed to simulate the forward speed of the aircraft on the ground, while an impact hammer mechanism is used to induce shimmy through a small initial tire slip. Weights can be used to induce vertical force exerted by the fuselage. The vibration signals are recorded using accelerometers, and processed numerically to obtain shimmy characteristics. A prototype of the novel shimmy damper designated as the Symmetric Torque Link Damper (STLD) is fabricated. The specifications of STLD are discussed in previous publications and summarized in the current paper. The experimental results including rotational vibration time histories, peak frequencies, and attenuation characteristics for the STLD are presented and compared with those of the baseline system without a shimmy damper, as well as with the built-in shimmy damper trends. Overall, this experimental work confirms the stability gain offered by the STLD, while it does not outperform the built-in damper in all scenarios. Instead, STLD has the attractive features of being retrofittable to existing landing gears and is symmetric in design, leading to an even distribution of dynamics loads on the gear. Furthermore, the testing apparatus presented in this work contributes to shimmy mitigation practice by offering a novel, yet simple, validation approach suitable for early prototype developments.

A Semi-Automatic Method to Measure the Rotation of Sunspots

Sunspots have been observed to undergo rotation about their umbral centre. This is typically a slow rotation, with even the fastest sunspot rotations only reaching angular velocities of a few degrees per hour. This rotation may inject magnetic energy into the Sun’s atmosphere, which can be stored in the coronal magnetic field and later released in eruptive events such as solar flares and coronal mass ejections. To usefully investigate rotating sunspots long periods of data need to be analysed, often of the order of several days, to build up a bulk rotation profile for the sunspot over time. This article outlines a semi-automated approach for analysing series of solar continuum data to extract the rotation profile of a sunspot as it transits across the solar disc. Moving towards an automated approach is vital for generating large, unbiased statistical samples of rotating sunspots in order to understand their contribution to solar activity. Existing methods typically focus on sunspots near disc centre for short time periods, neglecting much of the rotation history of the sunspot. The method is tested on six sunspots observed in continuum data from the Helioseismic and Magnetic Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO). These have been chosen to test the method for a range of different types of sunspots, including well-behaved sunspots, shape-changing sunspots, fast rotators, non-rotators, and interacting sunspots. The rotation profiles are compared by eye to animations of the sunspot from the data and are in acceptable visual agreement with the observed bulk rotation of the sunspot for all of the cases, except for the one which contains two sunspots in a shared penumbra. The method is also tested against sunspot rotations in active region (AR) 11158 that have been reported in the literature. While the results compare to some degree, the method outlined in this article reports lower rotations than those reported in the literature. Some of this discrepancy can be attributed to selection bias by the approaches in the literature, where only features that undergo larger rotation are tracked in sunspots that exhibit non-uniform rotation. The method also provides uncertainties on the calculated rotation profile which can be broken down to allow the principal sources of error to be identified. For the test sunspots in this article, the dominant source of uncertainty is the resolution of the SDO/HMI instrument.

The complex interplay between tidal inertial waves and zonal flows in differentially rotating stellar and planetary convective regions

Context.Quantifying tidal interactions in close-in two-body systems is of prime interest since they have a crucial impact on the architecture and the rotational history of the bodies. Various studies have shown that the dissipation of tides in either body is very sensitive to its structure and to its dynamics. Furthermore, solar-like stars and giant gaseous planets in our Solar System experience differential rotation in their outer convective envelopes. In this respect, numerical simulations of tidal interactions in these objects have shown that the propagation and dissipation properties of tidally excited inertial waves can be strongly modified in the presence of differential rotation.Aims.In particular, tidal inertial waves may strongly interact with zonal flows at the so-called co-rotation resonances, where the wave’s Doppler-shifted frequency is cancelled out. The energy dissipation at such resonances could deeply modify the orbital and spin evolutions of tidally interacting systems. In this context, we aim to provide a deep physical understanding of the dynamics of tidal waves at co-rotation resonances in the presence of differential rotation profiles that are typical of low-mass stars and giant planets.Methods.In this work, we have developed an analytical local model of an inclined shearing box that describes a small patch of the differentially rotating convective zone of a star or a planet. We investigate the propagation and the transmission of free inertial waves at co-rotation, and more generally at critical levels, which are singularities in the governing wave differential equation. Through the construction of an invariant called the wave action flux, we identify different regimes of wave transmission at critical levels, which are confirmed with a one-dimensional three-layer numerical model.Results.We find that inertial waves can be fully transmitted, strongly damped, or even amplified after crossing a critical level. The occurrence of these regimes depends on the assumed profile of differential rotation, on the nature as well as the latitude of the critical level, and on wave parameters such as the inertial frequency and the longitudinal and vertical wavenumbers. Waves can thus either deposit their action flux in the fluid when damped at critical levels, or they can extract action flux from the fluid when amplified at critical levels. Both situations can lead to significant angular momentum exchange between the tidally interacting bodies.

Awareness and Knowledge Among Internal Medicine House-Staff for Dose Adjustment of Cardiovascular Drugs in Chronic Kidney Disease.

Patients with chronic kidney disease (CKD) are vulnerable to adverse-drug events from cardiovascular drugs. To evaluateawareness and knowledge for appropriate dose adjustment of cardiovascular drugs in CKD patients among Internal Medicine house-staff (IMHS). Cross-sectional convenience sample survey in Fall 2015 among 341 IMHS from multiple academic institutions in the suburban New York City metropolitan area. Awareness was whether drug dose adjustment was needed. Knowledge was correct GFR level for drug dose adjustment. Multivariate logistic regression was conducted. We found overall high percentages and high odds for all cardiovascular drugs for incorrect awareness and knowledge. Postgraduate year (PGY)-1 had greater odds than PGY-3 for Carvedilol (OR: 5.56, 95% CI: 2.19-14.12, p < 0.001) and Digoxin (OR: 3.87, 95% CI: 1.37-10.95, p < 0.05), and lesser odds than PGY3 for Atenolol (OR: 0.31, 95% CI: 0.10-0.91, p < 0.05). Nephrology exposure during medical school rotation, renal clinic, or family history had lesser odds for Carvedilol (OR: 0.45, 95% CI: 0.21-0.97, p < 0.05), Simvastatin (OR: 0.40, 95% CI: 0.16-0.97, p < 0.05), and Hydralazine (OR: 0.31, 95% CI: 0.12-0.81, p < 0.05). Nephrology exposure during residency (OR: 1.96, 95% CI: 1.10-3.50, p < 0.05) and US osteopathic graduates (OR: 2.40, 95% CI: 1.04-5.50, p < 0.05) each had greater odds for Enalapril (OR: 2.40, 95% CI: 1.04-5.50, p < 0.05). International medical graduates had lesser odds than US graduates for Amlodipine (OR: 0.30, 95% CI: 0.11-0.82, p < 0.05). IMHS had overall poor awareness and knowledge for dose adjustment for common cardiovascular drugs in patients with CKD. As the majority of CKD patients are managed by their primary care providers, training programs should ensure that IMHS have adequate education in Nephrology during their residency training.

The Effect of Crop Rotation and Cultivation History on Predicted Carbon Sequestration in Soils of Two Experimental Fields in the Moscow Region, Russia

Soil organic carbon (SOC) sequestration in arable soils is a challenging goal. We focused on the effect of crop rotation and previous land use for future carbon sequestration on two experimental fields on Retisols with four contrasting fertilization treatments each. We analyzed the SOC dynamics and used the RothC model to forecast the SOC. We found a consistent increase in SOC stocks and stable fractions of the soil organic matter (SOM) with C accumulation in the next 70 years compared to the 90-year experimental period, more evident under the Representative Concentration Pathway 4.5 (RCP4.5) compared with the RCP8.5 scenario. The expected increase in SOC will be higher in the crop rotation with a grass field than in the experiment with an alternation of row crops and cereals. The efficiency depended on stable SOM fractions, and fields with more extended cultivation history showed higher SOM stability. Proper crop rotations are more important for SOC stability than the uncertainty associated with the climate change scenarios that allows timely adaptation. The goal of a 4‰ annual increase of SOC stocks may be reached under rotation with grasses in 2020–40 and 2080–90 when applying a mineral or organic fertilizer system for scenario RCP4.5 and a mineral fertilizer system in 2080–2090 for scenario RCP8.5.

Experimental and numerical studies of concrete-encased concrete-filled steel tube stub columns under uniaxial and biaxial eccentric compression

Experimental and numerical studies were conducted to investigate the structural performance and resistances of concrete-encased concrete-filled steel tube (CECFST) stub columns under uniaxial and biaxial eccentric compression. A test programme, consisting of 1 axially-loaded stub column, 3 uniaxial-eccentrically-loaded stub columns and 11 biaxial-eccentrically-loaded stub columns, was firstly conducted. The effects from uniaxial and biaxial loading eccentricities and end moment ratios on the structural performance of CECFST stub columns were studied. The key test results, including the failure load and mode of each specimen, crushing and spalling of the concrete cover, load–deflection and moment–curvature curves, were presented. It was found that the loading eccentricity and end moment ratio affect the ductility and failure mode of the specimen. The mid-height moment capacity of each specimen was maintained by the inner CFST after the outer concrete encasement was crushed. The test programme was followed by a numerical modelling programme, where finite element models were initially developed and validated against the experimental results, including the full load–deflection curves and end moment–rotation histories, and then adopted for conducting parametric studies to generate additional numerical data. The obtained test and numerical data were then used to evaluate the applicability of the codified design approaches in the American specification (Method 1 and 2), European code, and AIJ standard for composite columns under eccentric compression. The results of the evaluations revealed that the European code and American specification (Method 2) overestimate the cross-section resistances of CECFST stub columns under uniaxial eccentric compression, while the AIJ standard and American specification (Method 1) provide conservative resistance predictions. For CECFST stub columns subjected to biaxial eccentric compression, both the European code and American specification (Method 2) underestimate the cross-section resistances. Finally, new design methods were proposed for CECFST columns under uniaxial and biaxial eccentric compression, indicating a higher level of design accuracy over the design codes.

Root-associated Burkholderia spp. on the hairy vetch (Vicia villosa Roth.) cover crop vary depending on soil history of use

Vicia villosa is a cover crops commonly introduced in the rotation schema of sustainable agricultural practices. As a leguminous crop, Vicia villosa interacts with rhizobia to fix atmospheric nitrogen, modifying the nutritional status of consecutive crops. The interaction with other probiotic bacteria is, however, unknown. Burkholderia spp. are dominant members of rhizosphere, providing biological functions to promote plant growth. To recognize the interaction of the hairy vetch with the relevant plant related Burkholderia spp. species we performed microcosm experiments with soils having different history of use. Results showed that populations size of Burkholderia spp. on Vicia roots were similar for all treatments irrespective of land uses history. However, Vicia villosa was able to recruited different diversity of root associated Burkholderia spp. species, ressembling the populations structure in the bulk soils. Root-associated Burkholderia spp. were mainly enriched in strains with already recognized interactions with plants. These results suggest that bulk soils with a history of crop rotation instead of monocropping contribute with a higher diversity of Burkholderia spp. species capable of interacting with hairy vetch roots.

Weed infestation is affected by chickpea farmer demographics and agronomic practices

AbstractTo investigate the effects of agronomic practices and farmer demographics on levels of weed infestation in chickpea fields, a survey was conducted during 2015 in Sanjabi district, Kermanshah, Iran. Two sets of data were collected: (a) weed sampling from the selected chickpea fields, and (b) questionnaire recording of farmer demographics and agronomic management. The farmers were asked about their residence status (resident or migrant), occupation (farming only, farming plus a second job), experience and education levels, as well as seedbed preparation, sowing date and method, source of seed supply, crop cultivar, sowing seed rate, weed control operation and crop rotation history. The results showed that weed species composition was similar across the studied fields. The use of a row crop planter, a sowing rate of 45 kg ha‐1, and weed control resulted in 30.2, 23.03 and 34.2% reductions in weed infestation compared with hand sowing, a sowing rate of 30 kg ha‐1 and lack of weed control, respectively. Weed density decreased with increasing farmer experience and decreased by 33.0% and 23.5% in chickpea fields of resident farmers and owners whose sole occupation was agriculture. We found that 89.5% of the most experienced farmers adopted weed control operations and most resident landowners (77.4%) opted for crop planter (77.4%) and weed control (90.3%) compared to migrant farmers (50 and 68.5%, respectively). More landowners who were exclusively farmers performed weed control (90.6%) than owners who had a second job (67.9%).

Orientation dependence of dislocation structure in surface grain of pure copper deformed in tension

Orientation dependence of dislocation structure in surface grain of pure copper deformed in tension was investigated and compared with that in bulk grain. Dislocation cell structure is dominated in [100]-[100] surface grain at a given strain, which follows the same rule with its bulk counterpart. For [110]-[110] and [110]-[111], bulk grains in a strain range are dominated by dislocation cell block structures, while surface grains with the same lattice rotation history can develop into either a cell block structure or dislocation cell/tangle structure, depending on the grain geometry and strain level. Dislocation structure evolution is postponed in surface grains due to the image force of the surface. The results indicate that dislocation evolution in surface grain of pure copper is not only orientation-dependent, but also strongly related with grain geometry.

Paleomagnetic data from the Precordillera of northern Chile: A multiphase rotation history related to a multiphase deformational history

One of the most conspicuous features of the Andean chain is the change in its trajectory from NW-SE to N-S at 18°S known as the Bolivian Orocline. Although the Central Andes rotation pattern (CARP) agrees roughly with the geometry of the orocline, large variations and greater than expected rotation magnitudes cannot be explained by a progressive oroclinal bending history alone.In this work, 621 oriented samples from Mesozoic and Cenozoic rocks in three different areas in the Precordillera of northern Chile, north of Calama, were analyzed. The samples were subjected to different demagnetization processes to isolate the characteristic magnetic remanence and calculate the tectonic rotations. By sampling pretectonic, syntectonic and post-tectonic units, the rotation history of different structural blocks was determined and related to specific deformational events. The results obtained from Lower Cretaceous units intruded or overlain by Upper Cretaceous units not rotated or recording smaller rotations indicate the existence of 20° clockwise and 20° counterclockwise rotated sites related to the Late Cretaceous Peruvian orogenic event. Data obtained from Upper Cretaceous-lowermost Paleocene rocks show areas slightly clockwise rotated (10–15°) and not rotated during the early Paleocene “K-T" deformation event. Remanence data from Upper Cretaceous-Eocene units across the area indicate as much as 20° clockwise rotation in the hanging wall of the Eocene Chintoraste-Quetena-Rabonas-Jaspe Reverse Fault System, whereas the footwall was unaffected. This Eocene rotation occurred during the early stages of the Eocene-Oligocene Incaic orogenic phase, prior to emplacement of the 40–37 Ma Fortuna Granodiorite Complex.Current models propose that rotations in CARP were entirely Cenozoic and largely accomplished in a single Paleogene event. Our data indicate that each of the Peruvian, K-T and Incaic deformation events contributed to CARP, with each event generating a non-uniform pattern of rotations which was superimposed on prior rotations in a non-uniform manner.

Characterization of clubroot (Plasmodiophora brassicae) from canola (Brassica napus) in the Peace Country of Alberta, Canada

Clubroot of canola (Brassica napus L.), caused by Plasmodiophora brassicae Woronin, has spread to more than 3000 fields in Alberta, Canada, since it was first identified in 2003, but the disease had not been reported in the Peace Country Region in the northwest of the province. In 2017, 21 cases of clubroot were found in Big Lakes County, the southeastern-most district in this region. In 2018, an additional five cases were identified. Surveys of the infested crops in 2017 detected a clubroot disease index (DI) of < 10% in 15 fields and > 10% in the other six, while in 2018, the DI was < 5% in four fields and > 50% in one. Canola had been grown 3–6 times over the preceding 7–8 years in all fields for which rotation histories could be obtained. A subset of 23 P. brassicae field isolates was evaluated for pathotype classification on the hosts of the Canadian Clubroot Differential (CCD) set. Of the isolates collected in 2017, 11 were pathotype 3H, two each were pathotypes 5I and 8N, and three had novel virulence patterns designated 5A, 8A, and 8B. The five field isolates tested from 2018 included pathotypes 6C, 8A and 8 N, plus two isolates of the novel pathotype 8C. On the differential system of Somé et al., 17 isolates were classified as pathotype P2 and six as P3. As the CCD pathotype 8C is virulent on clubroot-resistant canola, integrated disease management strategies will be required for resistance stewardship in this region.