Field-scale Experiments Research Articles

Horizontal single hole blast testing – Part 1: Systematic measurements using TLS surveys

Large scale Single Hole Blast (SHB) testing is used to characterize blasting behavior in a cost-effective manner. SHB testing provides the means to assess the effect of blasting specifications (e.g. burden dimension, explosive used, borehole diameter) on rock cratering and blast efficiency. The observed behavior depends significantly on the testing procedure and measurements recorded. Crater characteristics are commonly described by the displaced volume of rock and breakout shape. Analysis of SHB test results relies on reproducible measurements.This paper proposes a method for analysis of horizontal SHB tests using data collected via terrestrial laser scanning (TLS) surveys. The procedural algorithms, point cloud manipulations, and analysis facilitate systematic SHB testing, including the use of a reference axis aligned with the blasthole orientation. The definition of crater extents, absolute burden measurements, methods for crater slicing, and filtering are developed to maintain consistency with the plane strain assumption. Crater partitioning protocols are elaborated to enhanced details of captured data. A detailed workflow of the analysis is provided with examples from compiled field testing. The conventional SHB measurement approach for crater breakout angle is refined to account for superficial surface roughness, and to capture the full crater shape. Data captured for the craters is represented along the blasthole length to capture the plane-strain component of single blasthole cratering. Comprehensive results from full scale field experiments are presented in a companion paper.

Relaxation damage control via fatigue-hydraulic fracturing in granitic rock as inferred from laboratory-, mine-, and field-scale experiments

The ability to control induced seismicity in energy technologies such as geothermal heat and shale gas is an important factor in improving the safety and reducing the seismic hazard of reservoirs. As fracture propagation can be unavoidable during energy extraction, we propose a new approach that optimises the radiated seismicity and hydraulic energy during fluid injection by using cyclic- and pulse-pumping schemes. We use data from laboratory-, mine-, and field-scale injection experiments performed in granitic rock and observe that both the seismic energy and the permeability-enhancement process strongly depend on the injection style and rock type. Replacing constant-flow-rate schemes with cyclic pulse injections with variable flow rates (1) lowers the breakdown pressure, (2) modifies the magnitude-frequency distribution of seismic events, and (3) has a fundamental impact on the resulting fracture pattern. The concept of fatigue hydraulic fracturing serves as a possible explanation for such rock behaviour by making use of depressurisation phases to relax crack-tip stresses. During hydraulic fatigue, a significant portion of the hydraulic energy is converted into rock damage and fracturing. This finding may have significant implications for managing the economic and physical risks posed to communities affected by fluid-injection-induced seismicity.

Impact of managed stingless bee and western honey bee colonies on native pollinators and yield of watermelon: A comparative study

Watermelon (Citrullus lanatus) is an important crop cultivated in India and other warmer regions of the world. The crop is dependent on insect pollinators for its fruit set. However, information about pollination ecology in Indian states remains undetermined. We used a replicated field-scale experiment to identify the native pollinators and their foraging behaviour, including abundance, visitation rate, duration of visit, and pollination efficiency. We compared treatments with open-pollinated, hand-pollinated and the addition of two managed pollinator species to estimate the yield enhancement potential of managed stingless bees and western honey bees and their impact on native pollinator species. We found that ants, bees, butterflies, beetles, and wasps visited the flowers either for nectar, pollen, and/or floral tissue. Regarding the ‘pollinator importance’ value of the visitors, Halictus acrocephalus and Lasioglossum funebre were the most effective native pollinators. Despite their contribution, the plants showed a significant pollination deficit in the open-pollinated system which can be overcome by supplementary pollination services through the management of western honey bees (Apis mellifera) and/or stingless bees (Tetragonula iridipennis). However, the application of A. mellifera colonies greatly reduces the abundance, visitation rate and foraging time (amount of time spent per visit on a flower) of native pollinators. Hence, the utilization of managed stingless bee colonies for pollination services is more suitable and has a lesser impact on native pollinator species, which may lead to sustainable agricultural practices.

Preliminary assessment of chlorine reactivity with environmental materials accounting for boundary layer and maximum deposition effects

Many toxic industrial chemicals (TICs) such as chlorine and ammonia are very reactive with commonly encountered materials in the environment. The amount of TIC material reacted in the environment is an important factor in determining the impact of a release. Typically characterized with a dry deposition rate in atmospheric dispersion models, the reaction rate has predominately been studied in field scale experiments at concentration levels typical for air pollution (ppm levels). When considering the removal of chlorine by (dry) deposition in an episodic release, gas phase concentrations will be much higher than those associated with air pollution, and near-field reaction of chlorine with local vegetation will be strongly influenced by the response of leaves and other elements of the surface “canopy” to those high concentrations. In this work, standard engineering methods characterizing the rate of mass transfer from a fluid to a surface in conjunction with reaction at that surface are applied. Previous experimental programs that studied the removal of chlorine under conditions relevant to this study show that deposition of chlorine to plant material can reach a limiting maximum so that the plant material can no longer react with gaseous chlorine despite continued exposure. In the analysis presented here, it is shown that the effect of the maximum deposition can be treated using the same approach as has been used to model catalyst poisoning. This study developed a model to account for boundary layer resistance and the impact of maximum deposition in a framework that could be incorporated in atmospheric dispersion models. To test the efficacy of this model, the Controlled Environment Reactivity Test (CERT) apparatus was designed to expose selected environmental materials (substrates including soil, rye grass, white clover, maple leaves, and spruce branches) to chlorine with initial concentration of (nominally) 1000 ppm where the gas phase chlorine concentration can be measured as a function of time to determine relevant modeling parameters. The apparatus was built to control the flow velocity of the chlorine/air mixture over the experimental substrates with turbulence levels that are comparable to the atmosphere. Model parameters were found for the environmental materials tested.

Use of Biochar for Limiting the Pathway of Exposure and Reducing the Risk of Heavy Metal Contamination from Mines

Field-scale experiments were conducted to assess biochar’s ability with and without supplements to sequester heavy metals of lead (Pb2+) and zinc (Zn2+) from stream water contaminated by abandoned mines. The study was conducted at the Frongoch mine watercourse site in central Wales for 1104 h (46 days). The methods employed include pyrolysis of waste Leylandii feedstocks at 700 °C and post-amendment ash at ratios in mass (kg/kg) 1:10, 1:35, 1:50, and 1:100 of biophos to biochar (BC) and 1:1:100 mixed biophos and cockleshell ash to biochar (CBB). The collected data were analyzed by ASTM Brunauer-Emmett-Teller (BET), XRF spectrometer, R-stat, and SPSS statistical procedures. The results showed that non-amended samples are better suitable as adsorbent materials of lead and zinc. Overall, this field study showed that 33 g/kg of lead and 30 g/kg of zinc could be sequestered by 50 g of biochar (BC) and activated carbon (AC) from the contaminated mine watercourse containing 0.62 mg/L and 15.8 mg/L of lead and zinc metals flowing at 0.014 m3/s. These adsorbent materials BC and AC applications are variably recommended at an optimal replacement interval of 1104 h (46 days) and 72 h (3 days) for lead and zinc sorption, respectively.

Field-Scale Improvement of Water Allocation for Maize Cultivation Using Grey Wolf Optimization Algorithm

It is necessary to develop methods to improve soil moisture capacity and agricultural productions in arid and semiarid areas. This study was conducted to evaluate the impact of optimal water allocation to improve the yield production in Gotvand Plain, Khuzestan Province, south-western Iran. A field-scale experiment with three scenarios of sugarcane bagasse compost application (0, 15 and 30 ton/ha) and four levels of water supply (50%, 75%, 100% and 125% of total allowable water) was performed in three replications (March–July 2019). Porous media texture, infiltration rate and irrigation demand were simulated at daily time steps to provide the root zone moisture content using real-time analysis of soil water balance. Furthermore, the maximization of readily available water based on the agricultural demand were considered using grey wolf optimization algorithm under deep percolation and runoff constraints. The results showed that the water allocation strategies and compost scenarios can improve water use efficiency and soil moisture.

Assessing the hydraulic and mechanical impacts of heat generating radioactive waste at the whole repository scale

Radioactive waste disposal facilities for heat generating waste are designed to maintain a compressive stress regime in the host rock. Field-scale tests have been undertaken to study how heating of the host rock can reduce the effective stress on the rock. However, it is not possible to carry out experiments at the scale of a whole repository (km-scale), so variation of host rock properties that might be encountered at this scale is not captured by the experiments.Previous numerical modelling of field scale experiments has demonstrated that the physical processes leading to changes in the stress regime are well understood. Here those models are applied at the km-scale, considering approaches to representing a whole repository and the effect of variability in the properties of the host rock. A dataset from the Callovo-Oxfordian Claystone at the Meuse/Heute-Marne Underground Rock Laboratory is used to characterise the natural variability of a potential host rock at the scale of a disposal facility.The modelling demonstrates that for understanding the generation of thermal stresses, considerable learning can be gained from models that employ symmetry conditions and represent a small part of the repository, hence reducing the size of the computational problem. The host rock at the mid-point between waste cells remained in vertical compression for all the parameter combinations used, which builds confidence that horizontal fracturing of the host rock between waste cells due to thermal pressurisation is unlikely for the disposal concept discussed here. Ground surface uplift was also considered and is in the range of 9–13 cm for disposal system studied.Spatial variability in the properties of the host rock has the potential to lead to significant variability in temperature, pressure, effective stress and displacement around the facility. In particular, thermal conductivity, permeability, Young’s modulus and coefficient of thermal expansion need to be well characterised.

Simultaneous immobilization of arsenic and cadmium in paddy soil by Fe-Mn binary oxide

Paddy soil in south China has long been haunted by the co-contamination of arsenic (As) and cadmium (Cd), resulting in the relatively high accumulation of As and Cd in rice, which puts humanity into a food safety dilemma. Therefore, it is paramount to restrain the migration of contaminants from soil to rice grains to cushion their impact on human health. However, the opposite biogeochemical behaviors of As and Cd in paddy soils under flooding condition make it a great challenge to simultaneously immobilize both As and Cd, particularly for the large-scale remediation. In this work, lime, Fe2O3, and Fe-Mn binary oxides (FM) were performed for immobilizing As and Cd in paddy soil at a field-scale experiment, and their associated mechanisms were discussed. Results showed that 0.10 wt% of Lime reduced Cd in grain (36.68%), 0.60 wt% of Fe2O3 decreased the accumulation of As and Cd (28.32% and 26.91%, respectively), and 0.60 wt% of FM significantly decreased As and Cd (42.42% and 36.49%, respectively). Analytical results of As speciation in rhizosphere soils demonstrated that FM played a dual role in oxidation and adsorption toward As immobilization. The DGT-measured As and Cd concentrations in rhizosphere soils showed that 0.60 wt% of FM significantly reduced the bioavailability of As and Cd in the paddy soil by 65.63% and 52.98%, respectively. Moreover, 0.60 wt% of FM promoted the formation of Fe/Mn-plaque on root surface, which significantly enhanced the adsorption of As and Cd upon Fe/Mn-plaque (44.06% and 32.14%, respectively) and further inhibited the uptake of As and Cd by rice. Hence, the mechanism for As and Cd immobilization by FM can be summarized: (1) oxidation of As(III) to As(V) and transformation and immobilization of As and Cd in rhizosphere soil and (2) promotion of Fe/Mn-plaque formation on root surface to retard the uptake of As and Cd by rice. These efforts attempt to set up a theory-to-practice solution for remediating As and Cd co-contamination in paddy soil.

Design and development of a low-cost automatic runoff sampler for time distributed sampling

Monitoring sediment yield is necessary for assessing erosion induced land degradation and used for planning conservation measures. Collecting time and space integrated as well as time distributed runoff samples cost-effectively is still a challenge for hydrologists, civil engineers, soil scientists, and environmentalists. A low-cost automatic runoff sampler for quantifying suspended sediment using simple mechanical and hydraulic principles was designed, and a prototype developed. The procedure of runoff sampling involves the interception of a defined portion of the runoff exiting the crest of a gauging structure through the triangular sectioned interceptors. The intercepted volume was reduced to a manageable quantity by multiple splitting using a series of diamond sectioned interceptors. After the collection of a representative volume, the sample was delivered to a time-stamped storage system through a clock-driven arm tube. The mathematical design principles at each stage defined the hydraulic and mechanical dimensions of the components which were assembled to develop the complete prototype. Furthermore, field-scale modifications to accommodate any special situations and conditions were also presented. The prototype of the sampling device endured rigorous laboratory-scale validation tests and was found to perform reasonably well. The performance of the new sampling device was evaluated against the fine resolution manual discrete sampling. The temporal resolution of 15 min adopted by the sampler was found reasonably comparable to further finer resolution options with discrepancies contained within a ± 10% error envelope (R2 = 0.983). The equipment was validated in field-scale experiments both in plot and natural watershed and performance metrics were found to be acceptable (R2 = 0.78 to 0.99). Moreover, low cost and easy maintenance requirements indicate the high potential and field applicability of this new device.

Understanding Contaminant Migration Within a Dynamic River Corridor Through Field Experiments and Reactive Transport Modeling

The behavior of a persistent uranium plume within an extended river corridor at the DOE Hanford site is dominantly controlled by river stage fluctuations in the adjacent Columbia River. The plume behavior is further complicated by substantial heterogeneity in physical and geochemical properties of the host aquifer sediments. Multi-scale field and laboratory experiments and reactive transport modeling were integrated to understand the complex plume behavior influenced by highly variable hydrologic and geochemical conditions in time and space. In this paper, we (1) describe multiple data sets from field-scale uranium adsorption and desorption experiments performed at our experimental well-field, (2) develop a reactive transport model that incorporates hydrologic and geochemical heterogeneities characterized from multi-scale and multi-type datasets and a surface complexation reaction network based on laboratory studies, and (3) compare the modeling and observation results to provide insights on how to refine the conceptual model and reduce prediction uncertainties. The experimental results revealed significant spatial variability in uranium adsorption/desorption behavior, while modeling demonstrated that ambient hydrologic and geochemical conditions and heterogeneities in sediment physical and chemical properties both contributed to complex plume behavior and its persistence. This research underscores the great challenges in adequately characterizing this type of site to model the reactive transport processes over scales of 10 m or more. Our analysis provides important insights into the characterization, understanding, modeling, and remediation of groundwater contaminant plumes influenced by dynamic surface water and groundwater interactions.

Mechanism and role of seeded native grasses to immobilize nitrogen on harvested blanket peat forests for protection of water courses.

Forest harvesting activities on peatlands have long been associated with nutrient leaching and deterioration of downstream water quality. This study aims to assess the effect of grass seeding practice on harvested blanket peatlands to immobilize N and reduce its export to water courses. First, a plot-scale field experiment was conducted by seeding with two grass species (Holcus lanatus and Agrostis capillaris) to study the N uptake potential from a harvested area. Secondly, a simulated rainfall experiment was conducted to study the effect of these grasses on reducing N leaching from surface peat using laboratory flume approach. In the end, the role of seeded grasses in removing N from nutrient-rich throughflow water was assessed using simulated overland flow experiment. The results showed that the seeded grasses had the potential to uptake over 30 kg ha-1 of N in the first year after seeding on harvested peatlands, whereas it takes over 2.5 years to establish the same level of N uptake by natural re-vegetation (non-grassed). In the simulated rainfall experiment, the inorganic N (NH4+-N and NO3--N) leaching in surface runoff from grassed flumes was 72% lower (453 mg m-2) than non-grassed flumes (1643 mg m-2). In the simulated overland flow experiment, the N retention by grassed flumes was significantly higher (98%) as compared to non-grassed flumes (70%) in the simulated overland flow experiment. Comparatively higher concentrations of NH4+-N and NO3--N in soil porewaters of non-grassed flumes suggest that this N retention by non-grassed flumes is less sustainable and is likely to be leached in runoff in subsequent flow events. The results from all three experiments in this study suggest that seeded grasses are a major sink of N on harvested blanket peatland forests. Immobilization of N onsite using the grass seeding and mini-buffer practice could be an efficient and a feasible mean of reducing N export from harvested blanket peatland forests in order to protect the sensitive water courses. However, the sustainability of retention and immobilization of N by grasses needs to be studied further in long-term field-scale experiments on multiple peatland sites.

Hydrology and rainfall runoff pollutant removal performance of biochar-amended bioretention facilities based on field-scale experiments in lateritic red soil regions

Bioretention has been found to lower the effluent loads of various pollutants from rainfall runoff. However, it is still a challenge to effectively use bioretention for rainfall runoff control in lateritic red soil regions where have high rainfall intensity and low soil infiltration capacity. Hence, in this study, the hydrologic performance and rainfall runoff pollutant removal capacity of field-scale biochar-amended bioretention facilities were tested with four rainfall recurrence periods under different biochar distributions, internal water storage (IWS) zone heights, and exfiltration conditions. The results confirmed that incorporation of biochar into planting soil would improve its water content raising capacity (WCRC), especially when the biochar was uniformly mixed with the lateritic red soils. Besides, more infiltrating from the planting soil layer and higher IWS zone heights effectively enhanced WCRC of the stone chip packing layer. For runoff volume control, adding biochar and increasing the IWS zone height could effectively improve runoff volume control capacity. Besides, the unlined bioretention had a higher runoff volume control capacity than lined bioretention. Considering runoff pollutant removal performance, biochar could contribute to significantly improving the runoff pollutant event mean concentration removal rate (Rc) of nutrient pollutants (TN, NO3-N, NH3-N, and TP). The average runoff pollutant load removal rate (Rl) of different biochar distributions decreased as follows: biochar was uniformly mixed with the lateritic red soils > biochar was stratified with the lateritic red soils > biochar was excluded in the planting soil layer. The average Rc and average Rl of all pollutants except COD under different IWS zone heights decreased as follows: 40 cm > 20 cm > 0 cm. Meanwhile, the average Rl of the lined bioretention with an IWS zone height of 0 cm was lower than that of the unlined bioretention. Overall, higher rainfall recurrence periods would reduce the treatment capacity of bioretention facilities.

Options for statistical analysis of unreplicated paired design drainage experiments

Field scale experiments are seldom replicated due to size constraints and limitations of other resources. This presents a difficulty in performing statistical analysis and interpretation of the results collected. In this paper we will evaluate water and nutrient effluent data from two fields, one managed under controlled subsurface drainage (CSSD) compared with an adjacent field under conventional free subsurface drainage (FSSD). The purpose of this paper is to compare approaches for statistical analysis of unreplicated paired design drainage experiments. The methods tested include the paired watershed design, a before-after control-impact paired (BACIP) design, time-series, and analysis using a beta and a gamma distribution. The assumptions used in the paired watershed and BACIP designs require the data to follow a normal distribution with identically and independently distributed errors, while the beta and gamma distributions do not require the assumption of normality. Analysis of the data set using a normal distribution was found to be inappropriate due to the nature of the data set which violates the assumptions required for analysis of variance; whereas, the analysis of the data using a beta distribution was found to produce the most appropriate results. The time series approach mimicked the physical treatments applied to FSSD and CSSD fields and led to a significant effect of CSSD compared to FSSD. Future work should focus on confirming that the beta distribution or time series are the best approaches for statistical analysis of field scale unreplicated paired design drainage experiments.

MicroRNA-based markers as a tool to monitor the barley (Hordeum vulgare L.) response to soil compaction

Plants are often exposed to adverse environmental conditions that can significantly interfere with their genomic response. Soil compaction induced by heavy field machinery represents a major problem for crop production mainly due to restricted root growth and penetration into soil and therefore reduced water and nutrient uptake by the plants. Tested hypotheses were to declare whether the plant‘s genome responds to soil compaction and whether the microRNA-based markers are suitable to determine this response. A long term field scale experiment was established in 2009 where different levels of soil compaction are researched from the soil and crop point of view. The analyzed barley (Hordeum vulgare L.) plants were collected during the growing season in 2019. The effect of soil compaction was analysed by four different DNA-based markers corresponding to miRNA sequences of dehydratation stress-responsive barley miRNAs (hvu-miR156, and hvu-miR408) and nutrition-sensitive markers (hvu-miR399 and hvu-miR827), within the leaf, stem and root tissues of barley plants. Our preliminary data support hypotheses that plant genome response was tissue-specific due to significant induction of the biomarkers to dehydratation and nutrition stress. The most affected part of the plant by dehydration, were roots and lack of nutrient supply was most pronounced on leaves.

Desiloxanation process of biogas using an amorphous iron hydroxide-based adsorbent: A comparison between laboratory and field-scale experiments

Amorphous iron hydroxide-based material was selected as a suitable adsorbent for the siloxanes from biogas and landfill gas. The adsorptive characteristics of the desiloxanation (DeSiloxs) process were studied through a lab-scale experiment using a simulated gas containing a mixture of siloxanes (D4, and D5) and a field experiment on an actual environment scale. The iron hydroxide-based adsorbents exhibited high activity in adsorption of siloxanes during lab-scale experiments, where the obtained adsorption capacity was about 26.3 % with N2 as a carrier gas. However, from an applicability point of view, the effectiveness of the siloxane removal process was significantly affected by the space velocity during the in-situ test in anaerobic digestion gas plant using wastewater sludge. In the experimental case of various space velocities (50, 100, 300 h−1), a very high removal efficiency (100 %) was obtained.

The effect of dynamic near-wake modulation on utility-scale wind turbine wake development

High-resolution field-scale experiments using flow visualization with natural snowfall and high-fidelity large eddy simulations are combined to investigate the effect of dynamic turbine operation and atmospheric conditions on wind turbine wake mixing and recovery in the wake of a 2.5 MW wind turbine. Instantaneous near-wake expansion and deflection in response to changes in blade pitch and wind direction, termed dynamic wake modulation, is quantified using both techniques, demonstrating excellent agreement. The simulations are used to extend these results by calculating the energy flux into the wake 7 rotor diameters downstream, showing that dynamic turbine-atmospheric interactions enhance mixing in the far-wake. This finding is exhibited under both uniform and turbulent inflow conditions. Under turbulent flow, a synergistic relationship is also observed between dynamic wake modulation and wake meandering, as wake recovery can be further accelerated when the two phenomena occur together. The results of this study have implications for the development of more realistic far-wake models that include the significant impact of dynamic wake modulation on wake mixing and development. Additionally, the findings from the current study can be used to develop advanced control algorithms to speed up wake breakdown and recovery, further improving wind farm efficiency.

Mine Waste Rock: Insights for Sustainable Hydrogeochemical Management

Mismanagement of mine waste rock can mobilize acidity, metal (loid)s, and other contaminants, and thereby negatively affect downstream environments. Hence, strategic long-term planning is required to prevent and mitigate deleterious environmental impacts. Technical frameworks to support waste-rock management have existed for decades and typically combine static and kinetic testing, field-scale experiments, and sometimes reactive-transport models. Yet, the design and implementation of robust long-term solutions remains challenging to date, due to site-specificity in the generated waste rock and local weathering conditions, physicochemical heterogeneity in large-scale systems, and the intricate coupling between chemical kinetics and mass- and heat-transfer processes. This work reviews recent advances in our understanding of the hydrogeochemical behavior of mine waste rock, including improved laboratory testing procedures, innovative analytical techniques, multi-scale field investigations, and reactive-transport modeling. Remaining knowledge-gaps pertaining to the processes involved in mine waste weathering and their parameterization are identified. Practical and sustainable waste-rock management decisions can to a large extent be informed by evidence-based simplification of complex waste-rock systems and through targeted quantification of a limited number of physicochemical parameters. Future research on the key (bio)geochemical processes and transport dynamics in waste-rock piles is essential to further optimize management and minimize potential negative environmental impacts.

Addressing Validity and Generalizability Concerns in Field Experiments

In this paper, we systematically analyze the empirical importance of standard conditions for the validity and generalizability of field experiments: the internal and external overlap and unconfoundedness conditions. We experimentally varied the degree of overlap in disjoint sub-samples from a recruitment experiment with more than 3,000 public schools, mimicking small scale field experiments. This was achieved by using different techniques for treatment assignment. We applied standard methods, such as pure randomization, and the novel minMSE treatment assignment method. This new technique should achieve improved overlap by balancing covariate dependencies and variances instead of focusing on individual mean values. We assess the relevance of the overlap condition by linking the estimation precision in the disjoint sub-samples to measures of overlap and balance in general. Unconfoundedness is addressed by using a rich set of administrative data on institution and municipality characteristics to study potential self-selection. We find no evidence for the violation of unconfoundedness and establish that improved overlap, and balancedness, as achieved by the minMSE method, reduce the bias of the treatment effect estimation by more than 35% compared to pure randomization, illustrating the importance of, and suggesting a solution to, addressing overlap also in (field) experiments.

Quantifying Early-Season Pest Injury and Yield Protection of Insecticide Seed Treatments in Corn and Soybean Production in Ontario, Canada

A 4-yr study was conducted comparing the efficacy and value of fungicide-only (FST), neonicotinoid insecticide + fungicide (NST), and diamide insecticide + fungicide (DST) seed treatments for commercial corn Zea mays L. and soybean Glycines max (L.) Merr. production in Ontario, Canada. Plant stand, plant vigor, above- and below-ground insect injury, and yield were assessed on 160 field-scale experiments. Experiments also assessed early-season insect incidence and abundance using newly legislated thresholds for NST use in Ontario and in-season destructive sampling. Wireworms (Coleoptera: Elateridae) and white grubs (Coleoptera: Scarabeidae) were frequently observed at experimental sites; however, thresholds were rarely met and injury levels rarely led to yield loss. Of 129 and 31 corn and soybean sites, 8 and 6%, respectively, had a positive yield response to NST use. Across all sites, yield response of 0.1 and -0.05 Mg ha-1 was observed with NST use in corn and soybean, respectively; however, the costs associated with NST use were recovered at only 48 and 23% of corn and soybean sites, respectively, based on average grain prices and yields during the study. Infrequent incidence of economic injury and the absence of a consistent yield response to NST and DSTs throughout the 4 yr of the study indicate that widespread use of seed-applied insecticides in corn and soybean is unlikely to provide benefit to producers. These data highlight an opportunity for reducing input costs, environmental loading, and nontarget effects without adverse outcomes for Ontario producers.

Advanced approach for screening soil with a low radiocesium transfer to brown rice in Fukushima based on exchangeable and nonexchangeable potassium

Phytoavailable K in soil is a key to control the transfer factor of radiocesium from soil to brown rice. The transfer factors were determined for paddy fields cultivated in 2017 and 2018 under different K fertilization regimes in Fukushima Prefecture, Japan. Two phytoavailable forms of K, the exchangeable and nonexchangeable K contents were investigated for the surface soil sampled after the transplanting and fertilization as well as after harvest of rice in the same paddy fields. The exchangeable K content largely decreased from after transplanting and fertilization to after harvest, and the exchangeable K of the soil after harvest was negatively correlated with the transfer factor (rs = −0.70, p < .001). Most soil samples after harvest showed that the transfer factors exponentially increased as the exchangeable K decreased; however, some of the samples indicated considerably low transfer factors (<0.005) despite being exchangeable K deficient, i.e., exchangeable K < 25 mg K2O 100 g−1. Even though this value before usual fertilization has been effectively used as a threshold to determine whether supplemental K fertilization is required to reduce the radiocesium content in brown rice, additional screening was needed to estimate this radiocesium transfer more precisely. Thus, we found that not only the exchangeable K but also nonexchangeable K contents had a negative correlation with the transfer factor (rs = −0.60, p < .001) of the soil samples after harvest but were not correlated with each other (rp = −0.10). Furthermore, the results revealed that soil with nonexchangeable K > 50 mg K2O 100 g−1 indicated a considerably low transfer factor, even if exchangeable K deficient. Thus, via our field-scale experiments, we concluded that the criterion nonexchangeable K > 50 mg K2O 100 g−1 can be used as another threshold for use along with that of exchangeable K to differentiate soil with a low radiocesium transfer rate from exchangeable K deficient soil.