US Southern Great Plains Research Articles

Convectively Induced Secondary Circulations and Wind‐Driven Heat Fluxes in the Surface Energy Balance Over Land

AbstractIncreased resolution has enabled kilometer‐scale weather and climate models to partially resolve secondary circulations, including horizontal convective rolls (HCRs) and cold pool gust fronts. Although these circulations are ubiquitous in convective boundary layers over land, their impacts on the surface energy balance are largely unknown. Doppler lidar and surface observations were combined with DOE E3SM land model experiments, revealing increased surface winds (5 m/s) and heat fluxes (50 W/m2) in convergent branches of HCRs. Larger wind‐driven flux responses (up to 150 W/m2) were found along gust fronts. Surface energy balance shifts to accommodate wind‐driven fluxes, reducing ground heat conduction and longwave cooling. Our findings from the US Southern Great Plains are broadly relevant to modeling convective boundary layers. In particular, widely used subgrid wind gust parameterizations were found to be physically inconsistent with resolved secondary circulations and could worsen climate prediction biases at kilometer‐scales.

Estimating plant β-diversity using airborne and spaceborne imaging spectroscopy

ABSTRACT The increasing threats to grassland ecosystems from land-use/land-cover change, disturbances, and invasive species underscore the importance of monitoring grassland plant diversity. While most remote sensing studies have mainly focused on quantifying α-diversity (diversity within communities), less attention has been given to remotely estimating β-diversity (diversity between communities) in naturally-assembled grasslands. In this study, we used remote sensing to map plant β-diversity in a naturally-assembled grassland managed using prescribed fire and grazing in a North American tallgrass prairie ecosystem within the US Southern Great Plains. We aimed to assess the impact of time since fire on the relationship between in situ plant β-diversity and remotely–sensed β-diversity, also known as spectral β-diversity. We collected in situ observations at 60 m × 60 m, 120 m × 120 m, 180 m × 180 m, and 240 m × 240 m plots, alongside airborne and spaceborne DESIS imaging spectroscopy data with spatial resolutions of 1 m and 30 m, respectively. To assess how management practices influenced β-diversity, we grouped our in situ observations into three categories based on time since fire, including recently-burned (burn age <1 year), transitional (burn age of 1–2 years), and unburned (burn age >2 years). Our findings showed that the association between in situ and spectral β-diversity was strongly influenced by time since fire. Excluding plots with high soil cover (≥50%) improved our remote estimation of β-diversity, despite soil exposure effects. Our study demonstrated that remote sensing of β-diversity in grassland ecosystems is influenced by spatial scale, time since fire, and soil exposure, all of which can be addressed with scale-appropriate imaging spectrometry. This study also highlighted the capability of spaceborne imaging spectrometers to estimate β-diversity of grassland ecosystems across large spatial domains.

Influence of lower-tropospheric moisture on local soil moisture–precipitation feedback over the US Southern Great Plains

Abstract. ​​​​​​​Land–atmosphere coupling (LAC) has long been studied, focusing on land surface and atmospheric boundary layer processes. However, the influence of humidity in the lower troposphere (LT), especially that above the planetary boundary layer (PBL), on LAC remains largely unexplored. In this study, we use radiosonde observations from the US Southern Great Plains (SGP) site and an entrained parcel buoyancy model to investigate the impact of LT humidity on LAC there during the warm season (May–September). We quantify the effect of LT humidity on convective buoyancy by measuring the difference between the 2–4 km vertically integrated buoyancy with the influence of background LT humidity and that without it. Our results show that, under dry soil conditions, anomalously high LT humidity is necessary to produce the buoyancy profiles required for afternoon precipitation events (APEs). These APEs under dry soil moisture cannot be explained by commonly used local LAC indices such as the convective triggering potential and low-level humidity index (CTP / HILow), which do not account for the influence of the LT humidity. On the other hand, consideration of LT humidity is unnecessary to explain APEs under wet soil moisture conditions, suggesting that the boundary layer moisture alone could be sufficient to generate the required buoyancy profiles. These findings highlight the need to consider the impact of LT humidity, which is often decoupled from the humidity near the surface and is largely controlled by moisture transport, in understanding land–atmospheric feedbacks under dry soil conditions, especially during droughts or dry spells over the SGP.

Forage yield and nutritive value of summer legumes as affected by row spacing and harvest timing

Winter wheat (Triticum aestivum L.) is an essential, high-quality forage used for grazing stocker cattle from fall to spring in the US Southern Great Plains (SGP). However, the lack of nutritious forages during summers limits grazing by stocker cattle. To fill this quality gap, a short season species capable of producing significant yield and quality of forage is necessary. A two-year experiment was conducted to evaluate the performance of three legumes: tepary bean (Phaseolus acutifolius A. Gray), mothbean [Vigna aconitifolia (Jacq.) Marechal], and soybean [Glycine max (L.) Merr.] as a control, at different harvest dates, in response to different row spacing (38 ​cm and 76 ​cm) and moisture levels (rainfed and irrigated). Results showed forage yield by all legumes planted at 38 ​cm spacing (4.5 and 3.9 ​Mg ​ha−1) was higher than at 76 ​cm spacing (3.4 and 2.4 ​Mg ​ha−1) in 2018 and 2019. Soybean was the most productive while mothbean had the highest relative feed value (RFV) in both 2018 and 2019 (160 and 118, respectively). Although soybean produced more forage, mothbean and tepary bean provided high quality forage in terms of neutral detergent fiber (NDF), acid detergent fiber (ADF), and in-vitro true digestibility (IVTD). The results indicate that no single legume species stands out as the unequivocal leader in delivering both high-quality and abundant forage. Consequently, the choice of which species to utilize should be tailored to the specific forage requirements and management goals. Future research should explore mothbean genotypes to identify cultivars with greater yield potential and develop agronomic practices that effectively utilize those cultivars.

From Hydrometeor Size Distribution Measurements to Projections of Wind Turbine Blade Leading-Edge Erosion

Wind turbine blade leading-edge erosion (LEE) is a cause of increased operation and maintenance costs and decreased annual energy production. Thus, detailed, site-specific quantification of likely erosion conditions are critically needed to inform wind plant owner/operator decisions regarding mitigation strategies. Estimating the damage potential at a wind plant site requires accurate measurement of precipitation intensity, phase, droplet size distributions, wind speeds and their joint statistics. The current work quantifies the effect of disdrometer type on the characterization of LEE potential at a site in the US Southern Great Plains. using observations from three co-located disdrometers (an optical, an impact and a video disdrometer), along with hub-height wind-speed observations from a Doppler lidar and two LEE models: a kinetic energy model and the Springer model. Estimates of total kinetic energy of hydrometeor impacts over the four-year study period vary by as much as 38%, and coating lifetime derived from accumulated distance-to-failure estimates from the Springer model differ by an even greater amount, depending on disdrometer type. Damage potential at this site is concentrated in time, with 50% of impact kinetic energy occurring in 6–12 h per year, depending on which set of disdrometer observations is used. Rotor-speed curtailment during the most erosive 0.1–0.2% of 10 min periods is found to increase blade lifetimes and lead to the lowest levelized cost of energy.

Towards a Unified Setup to Simulate Mid‐Latitude and Tropical Mesoscale Convective Systems at Kilometer‐Scales

AbstractMesoscale convective systems (MCSs) are the main source of precipitation in the tropics and parts of the mid‐latitudes and are responsible for high‐impact weather worldwide. Studies showed that deficiencies in simulating mid‐latitude MCSs in state‐of‐the‐art climate models can be alleviated by kilometer‐scale models. However, whether these models can also improve tropical MCSs and whether we can find model settings that perform well in both regions is understudied. We take advantage of high‐quality MCS observations collected over the Atmospheric Radiation Measurement (ARM) facilities in the US Southern Great Plains (SGP) and the Amazon basin near Manaus (MAO) to evaluate a perturbed physics ensemble of simulated MCSs with 4 km horizontal grid spacing. A new model evaluation method is developed that enables to distinguish biases stemming from spatiotemporal displacements of MCSs from biases in their reflectivity and cloud shield. Amazon MCSs are similarly well simulated across these evaluation metrics than SGP MCSs despite the challenges anticipated from weaker large‐scale forcing in the tropics. Generally, SGP MCSs are more sensitive to the choice of model microphysics, while Amazon cases are more sensitive to the planetary boundary layer (PBL) scheme. Although our tested model physics combinations had strengths and weaknesses, combinations that performed well for SGP simulations result in worse results in the Amazon basin and vice versa. However, we identified model settings that perform well at both locations, which include the Thompson and Morrison microphysics coupled with the Yonsei University (YSU) PBL scheme and the Thompson scheme coupled with the Mellor‐Yamada‐Janjic PBL scheme.

How Does Land Cover and Its Heterogeneity Length Scales Affect the Formation of Summertime Shallow Cumulus Clouds in Observations From the US Southern Great Plains?

AbstractThis study investigates the effects of heterogeneous land covers on shallow cumulus (ShCu) clouds at the US Southern Great Plains using high‐resolution satellite and land cover data. During late summer, ShCu occurs over cities the most frequently and over open waters the least frequently, and more often over forest than over grassland. The preferential occurrence of ShCu over forest relative to grassland is consistent with surface measurements showing larger heat fluxes over forests. This preferential occurrence also varies with the length scales of land patches with the largest cloud occurrence difference shifting from smaller length scales (&lt;9 km) during midday to larger scales (&gt;9 km) in the early afternoon. Consistent with theory, these signals are more pronounced under low wind conditions. The preferential length scale shift with time suggests the existence of secondary circulations that strengthen and promote convergence over larger spatial scales as the differential land surface heating intensifies.

Understanding the Roles of Convective Trigger Functions in the Diurnal Cycle of Precipitation in the NCAR CAM5

AbstractThe wrong diurnal cycle of precipitation is a common weakness of current global climate models (GCMs). To improve the simulation of the diurnal cycle of precipitation and understand what physical processes control it, we test a convective trigger function described in Xie et al. with additional optimizations in the NCAR Community Atmosphere Model version 5 (CAM5). The revised trigger function consists of three modifications: 1) replacing the convective available potential energy (CAPE) trigger with a dynamic CAPE (dCAPE) trigger, 2) allowing convection to originate above the top of planetary boundary layer [i.e., the unrestricted air parcel launch level (ULL)], and 3) optimizing the entrainment rate and threshold value of the dynamic CAPE generation rate for convection onset based on observations. Results from 1° resolution simulations show that the revised trigger can alleviate the long-standing GCM problem of too early maximum precipitation during the day and missing the nocturnal precipitation peak that is observed in many regions, including the U.S. southern Great Plains (SGP). The revised trigger also improves the simulation of the propagation of precipitation systems downstream of the Rockies and the Amazon region. A further composite analysis over the SGP unravels the mechanisms through which the revised trigger affects convection. Additional sensitivity tests show that both the peak time and the amplitude of the diurnal cycle of precipitation are sensitive to the entrainment rate and dCAPE threshold values.

Climatological sensitivities of shallow-cumulus bulk entrainment in continental and oceanic locations

AbstractCumulus entrainment is a complex process that has long challenged conceptual understanding and atmospheric prediction. To investigate this process observationally, two retrievals are used to generate multi-year climatologies of shallow-cumulus bulk entrainment (ϵ) at two Atmospheric Radiation Measurement cloud observatories, one in the US southern Great Plains (SGP) and the other in the Azores archipelago in the eastern North Atlantic (ENA). The statistical distributions of ϵ thus obtained, as well as certain environmental and cloud-related sensitivities of ϵ, are consistent with previous findings from large-eddy simulations. The retrieved ϵ robustly increases with cloudlayer relative humidity and decreases in wider clouds and cloud ensembles with larger cloud-base mass fluxes. While ϵ also correlates negatively with measures of cloud-layer vigor (e.g., maximum in-cloud vertical velocity and cloud depth), the extent to which these metrics actually regulate ϵ (or vice-versa) is unclear. Novel sensitivities of ϵ include a robust decrease of ϵ with increasing subcloud wind speed in oceanic flows, as well as a decrease of ϵ with increasing cloud-base mass flux in individual cumuli. A strong land–ocean contrast in ϵ is also found, with median values of 0.5-0.6 km−1 at the continental SGP site and and 1.0-1.1 km−1 at the oceanic ENA site. This trend is associated with drier and deeper cloud layers, along with larger cloud-base mass fluxes, at SGP, all of which favor reduced ϵ. The flow-dependence of retrieved ϵ implies that its various sensitivities should be accounted for in cumulus parameterization schemes.

Productivity and water use in intensified forage soybean-wheat cropping systems of the US southern Great Plains

Agro-ecological intensification of continuous dryland wheat ( Triticum aestivum L.) systems with forage soybean [ Glycine max (L.) Merr] in lieu of summer fallow could provide nutritious summer forage for livestock, reduce requirements for inorganic N fertilizer for winter wheat, and ameliorate sustainability issues associated with summer fallow, such as soil erosion and low precipitation use efficiency ( PUE ). This modeling study utilized DSSAT-CSM to assess: the yield and water use of three cultivars of forage soybean of diverse maturity groups (MGs) harvested at three different dates [60, 90, and 120 days after planting (DAP)]; and their influence on performance and water productivity of subsequent winter wheat, and overall double-cropping systems in comparison to the fallow-wheat system. Crop yield and evapotranspiration (ET) data, collected from continuous field experiments at El Reno, Oklahoma (35.57 °N, 98.03 °W) during 2002–2006, were used for calibration and validation of soybean and wheat models. Long-term simulations conducted using historical weather data (1994–2019) suggested that mid-maturity group (MGV) soybean could provide greater forage yields and higher water use efficiency ( WUE B ) than later-maturing soybeans (MGVI & MGVII) when harvested at 90–120 days after planting (DAP). Double-cropping forage soybean and winter wheat caused a reduction of 1.4-2.1 Mg ha −1 grain and 4.7-5.6 Mg ha −1 and biomass by wheat, and higher seasonal ET losses of 77−132 mm than the fallow-wheat system. However, trade-offs in yields between forage soybean and winter wheat were effective when precipitation was >180 mm during the first 60 d of growth by soybean. Despite yield losses in winter wheat, double-cropped forage soybean-wheat systems could be a viable option based on its economic competitiveness and other ecological benefits.

N2O Emissions From Residues of Oat and Grass Pea Cover Crops Cultivated in the US Southern Great Plains

Grass pea (Lathyrus sphaericus) and oat (Avena sativa) are potential cover crops for spring periods of summer crop systems in the US Southern Great Plains (SGP). The main objective of this study was to compare nitrous oxide (N2O) emissions from residues of grass pea and oat grown as green nitrogen (N) crops. The comparisons included responses from plots cultivated with oat, grass pea, and control (spring-fallowed) plots. Two management options were applied to grass pea: residues retained and aboveground biomass removed for forage. Crabgrass (Digitaria sanguinalis) was cultivated as a main summer crop immediately after termination of the cover crops. Fluxes of N2O were measured by closed chamber connected to a portable gas analyzer on 23 dates during a 3 month growing period for crabgrass. At termination, oat produced more aboveground biomass than grass pea (2.17 vs. 3.56 Mg ha−1), but total N in biomass was similar (102–104 kg ha−1) due to greater N concentrations in grass pea than oat (4.80% vs. 2.86% of dry mass). Three month cumulative emissions of N2O from grass pea-incorporated plots (0.76 ± 0.11 kg N2O-N ha−1; mean ± standard error, n = 3) were significantly lower than from oat-incorporated plots (1.26 ± 0.14 kg N2O-N ha−1). Emissions from grass pea plots with harvested biomass (0.48 ± 0.04 kg N2O-N ha−1) were significantly lower than those from grass pea-incorporated plots. Cumulative N2O emissions from control plots were significantly greater than those from grass pea-harvested plots but were similar to the emissions from grass pea-incorporated plots. Yields produced by crabgrass were similar from all cover crop treatments (8.65–10.46 Mg ha−1), but yield responses to the control (18.53 Mg ha−1) were significantly larger. Nitrogen concentrations in crabgrass were greater in response to oat- and grass pea-incorporated plots (2.86–2.87%) than in grass pea-harvested (1.93%) and control (1.44%) plots. In conclusion, the results indicated that (i) post-incorporation emissions of N2O can be greater from a non-legume green N crop than a legume green N crop due to greater biomass productivity of the cereal, and (ii) emissions of N2O could be mitigated by removing biomass of the green N crop for use as forage.

Simulating the Effects of Surface Energy Partitioning on Convective Organization: Case Study and Observations in the US Southern Great Plains

AbstractRealistic cloud‐resolving simulations were performed to study the effects of surface energy partitioning (surface sensible and latent heat fluxes) on the organization of isolated convection into larger mesoscale convective systems (MCSs) near the US Southern Great Plains. The role of cold pools in mediating surface‐convection interactions was explored. Better organized MCSs tended to occur in the experiments with perturbed wetter soil (and more active vegetation), regardless of the effects of soil moisture on the diurnal timing of convective triggering. Wetter soil led to shallower boundary layers and more convective available potential energy than drier soil. The roles of cold pools on convection are lifecycle‐stage dependent: A dry surface allows more numerous colliding cold pools, thereby aiding in convective triggering by reducing entrainment in the early stages, and providing gust‐front uplift in later stages. However, horizontal propagation of the cold‐pool density current can outrun the convective system, creating a slantwise updraft and thus weakening the gust front uplift in later stages. This effect calls into question previous cold pool parameterizations, in which the gust front uplift is mainly proportional to the negative buoyancy of cold air. Lastly, both the model and observation show an enhancement of surface latent heat flux during the passage of a gust front at night, suggesting that a positive feedback between the surface and convection helps MCSs to persist into the nighttime.

Soil water dynamics under a warm-season cover crop mixture in continuous wheat

Cover crop technology can potentially benefit monoculture wheat systems in the semi-arid US Southern Great Plains, but the biggest hurdle in such regions where evapotranspiration exceeds precipitation is soil water. Cover crop impact on soil water use and availability is a major cause for concern in water-limited environments. The objective of this study was to evaluate the impact of cover crops, grazing, and intercrops on soil water dynamics under rainfed conditions. Seven treatments were evaluated, including conventional tillage (CT) and combinations of no-tillage (NT) with a cover crop mixture, grazed cover crops, and/or cash crop intercropping. The three-year study was conducted on a long-term NT continuous wheat system in the Texas Rolling Plains. Despite dry periods, the cover crop mixture produced 2141 to 3503 kg ha−1 dry herbage mass. Stored soil water was significantly lower within 60 days after planting for cover crop compared to no cover crop treatments. Stored soil water was 22–26% lower in cover crop plots at time of termination. In the final two years of the study, the positive change in stored soil water from cover crop termination to wheat planting was two to four times greater for cover crop treatments compared to non-cover crop treatments. The greater infiltration and water capture after termination has the potential to make up for the loss in soil water that cover crops used.

Climate change impacts on wind power generation

Wind energy is a virtually carbon-free and pollution-free electricity source, with global wind resources greatly exceeding electricity demand. Accordingly, the installed capacity of wind turbines grew at an annualized rate of >20% from 2000 to 2019 and is projected to increase by a further 50% by the end of 2023. In this Review, we describe the factors that dictate the wind resource magnitude and variability and illustrate the tools and techniques that are being used to make projections of wind resources and wind turbine operating conditions. Natural variability due to the action of internal climate modes appears to dominate over global-warming-induced non-stationarity over most areas with large wind energy installations or potential. However, there is evidence for increased wind energy resources by the end of the current century in northern Europe and the US Southern Great Plains. New technology trends are changing the sensitivity of wind energy to global climate non-stationarity and, thus, present new challenges and opportunities for innovative research. The evolution of climate modelling to increasingly address mesoscale processes is providing improved projections of both wind resources and wind turbine operating conditions, and will contribute to continued reductions in the levelized cost of energy from wind power generation.

Ten Years of Aerosol Effects on Single-Layer Overcast Clouds over the US Southern Great Plains and the China Loess Plateau

Using almost 10 years of observations of clouds and aerosols from the US Southern Great Plains (SGP) atmospheric observatory and the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) in China, the impact of aerosols on single-layer overcast clouds over continental land for different regimes were investigated. Atmospheric conditions at the two sites were first compared in an attempt to isolate the influence of aerosols on cloud properties from dynamic and thermodynamic influences. Cloud types and amounts are similar at the two sites. The dominant aerosol types at the SGP and SACOL sites are sulphate and dust, respectively, with greater aerosol optical depths (AODs) and absorption at the SACOL site. Aerosol first indirect effect (FIE) ranges from 0.021 to 0.152 and from −0.078 to 0.047 at the SGP and SACOL sites, respectively, when using the AOD below cloud base as CCN proxy. Although differences exist, the influence of meteorological conditions on the FIE at the two sites is consistent. FIEs are easily detected under descending motion and dry condition. The FIE at the SGP site is larger than that at the SACOL site, which suggests that the cloud albedo effect is more sensitive under relatively cleaner atmospheric conditions and the dominating aerosol at the SACOL site has less hygroscopicity. The radiative forcing of the FIE over the SGP site is −3.2 W m−2 for each 0.05 increment in FIE. Cloud durations generally prolong as aerosol loading increases, which is consistent with the hypothesis of the aerosol second indirect effect. The negative relationship between cloud duration time and aerosol loading when aerosol loading reaches a large value further might suggest a semidirect effect.

Economic returns of one versus two fungicide applications in oklahoma winter wheat

AbstractFungicides protect winter wheat (Triticum aestivum L.) yield potential by managing foliar fungal diseases, but little information comparing one vs. two applications is available for the US southern Great Plains. Field experiments conducted from 2016–2018 at two Oklahoma locations (Apache and Stillwater) used two winter wheat cultivars (‘Gallagher’ and ‘Bentley’) and four fungicide application timings (control, Feekes 6, Feekes 9, and Feekes 6 + 9). Disease levels were highest during 2017 due to leaf rust. Dry conditions during 2018 limited disease development overall. Fungicide applications resulted in significantly higher yields in three of eight year × location × cultivar comparisons, all during 2017. The Feekes 6 + 9 treatment only showed the highest grain yield for the leaf rust‐susceptible cultivar Bentley at Stillwater that season. Partial profit was also examined by year, location, and cultivar using four fungicide cost scenarios at three grain sale prices. Only 22 of 96 comparisons showed significant positive partial profit from fungicide use, and all occurred at Stillwater during 2017. Two fungicide applications had the highest profit in 4 of the 22 comparisons for the cultivar Bentley. However, a single application of a low‐cost fungicide was most often among the highest profitable fungicide treatments, depending when higher disease levels were present. Partial profits from one and two fungicide applications were not significant or significantly negative when disease levels were low. Knowledge of cultivar disease susceptibility and disease scouting need to be considered to economically justify one or two fungicide applications in Oklahoma winter wheat.

Correction to: Greenhouse gas mitigation strategies for agronomic and grazing lands of the US Southern Great Plains

Correction to: Greenhouse gas mitigation strategies for agronomic and grazing lands of the US Southern Great Plains

Greenhouse mitigation strategies for agronomic and grazing lands of the US Southern Great Plains

Challenges to sustainable agriculture are increasing with forecasts for greater climate variability, including rising temperatures, extreme precipitation events, and prolonged droughts. One important factor that contributes to the increasing climate variability is greenhouse gas emissions, including from agro-ecosystems. The US Environment Protection Agency indicates soil management and enteric fermentation from livestock contribute ~ 80% of total greenhouse gas from agriculture sector. Management practices conducive to greenhouse gas emissions, and possible mitigation strategies for the agricultural systems of Southern Great Plains, an integral part of the US beef industry, have not been thoroughly defined. The objective of this paper is to review and synthesize the literature regarding management practices conducive to emissions [carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4)] from croplands and grazing lands of Southern Great Plains, and potential strategies that may aid in greenhouse gas mitigation in the region. The results from different published studies evaluating such strategies were analyzed to determine whether these practices have potential in mitigating greenhouse gas emissions from agronomic and grazing lands. Based on the analysis, it can be recommended that increasing the amount of cropland managed by conservation tillage, fertilizer management, crop rotation systems, grazing management, and fertilizer amendments can be potential management strategies for greenhouse gas mitigation. As agro-ecosystems are very complex and reducing emissions using strategies in one sector may stimulate higher emissions in other sectors, these strategies require testing at the systems-level before they can be implemented to advise applied policies for the Southern Great Plains region.

Plant Traits to Increase Winter Wheat Yield in Semiarid and Subhumid Environments

Core Ideas Wheat simulations occurred in over 2000 site–years for semiarid and subhumid climates.Limited transpiration trait increased wheat yield in 12 g m−2 in semiarid climate.Root exploration traits improved wheat yield by 60 g m−2 in semiarid climate.Faster leaf development trait increased wheat yield by 21 g m−2 across the entire study‐regionGenetic variability exists for the above traits for breeding programs to explore. Genetic variability exists for plant traits that confer drought tolerance to wheat (Triticum aestivum L.); however, there are limited quantitative assessments on the long‐term effects of these traits on wheat yield. As some of these traits might be detrimental in wet years, our objectives were to assess predicted winter wheat yield gains resulting from six altered traits in a moist subhumid to semiarid climate transition area. We used a mechanistic crop simulation model and daily weather data for 30 consecutive years at semiarid (n = 27), dry‐ (n = 23) and moist‐subhumid (n = 18) locations in the US Southern Great Plains. Modified traits were limited transpiration rate under elevated vapor pressure deficit, deeper root system, faster root development, early or late stomata closure in response to soil drying, faster or slower leaf area development, and shorter vegetative cycle. Probability of water‐deficit, defined as fraction of transpirable soil water (FTSW) &lt; 0.3 (i.e., limiting to transpiration), was 0.1 and 0.9 for the moist subhumid and semiarid environments, respectively. Increased root depth and rate of root development resulted in 35.5 to 87.3 g m−2 yield increases and probabilities of yield gain &gt; 0.7 in dry subhumid and semiarid environments. Faster leaf area development resulted in probabilities of yield gain &gt; 0.85 in subhumid environments. Limited transpiration rate increased grain yield by 12 g m−2 in semiarid environments. Neutral traits were early‐ and late‐stomatal closure in response to soil drying, reduced length of vegetative cycle, and slow rate of leaf area development.

Soil respiration from winter wheat-based cropping systems in the US Southern Great Plains as influenced by tillage managements

ABSTRACTThis study compared soil respiration (SR) fluxes from winter wheat-based cropping systems in the US Southern Great Plains (SGP) under reduced and conventional tillage. The study consisted of four sets of paired paddocks assigned to conventional or reduced tillage with a four-year crop rotation applied over time. During the 2016–2017 study year, four sets of paired paddocks were planted to: winter wheat managed for grazing, dual-purpose (grazing and grain production), and grain-only systems of production, and winter canola. Heterotrophic SR fluxes were measured using a plant and root exclusion method on eight permanently deployed PVC cores per paddock. Fluxes from the cores were measured manually using a closed chamber connected to an infrared gas analyser on 12–13 dates during the winter wheat growing season (October through May). There were strong seasonal patterns of SR flux, with lower rates during dry and cold periods, and higher rates during warm and wet periods. Large rainfall induced pulses of SR flux were observed for both tillage systems. There was no consistent large-scale difference in SR flux between tillage treatments applied to paired paddocks. Results from this study indicate SR fluxes from winter wheat-based cropping systems are controlled more by soil environmental conditions than form of tillage.