Polylactic acid (PLA) biobased mulches can reduce weed emergence in carrot ( Daucus carota ) production systems in which seeds are planted directly onto the mulch surface and top-dressed with compost to facilitate germination. However, PLA-based mulch can reduce early-season soil nitrate availability, which may stunt carrot growth. PLA mulches enriched with fertilizer may help mitigate soil nitrogen (N) immobilization. The objective of this 2-year field study was to develop prototype PLA mulches enriched with organic fertilizer and evaluate potential tradeoffs among soil fertility, weed suppression, and carrot yield. Six mulch types that varied in fertilizer type and rate were tested in combination with compost top-dressings from two different feedstocks (mixed or yard waste) and compared with controls with compost only, no mulch, or compost. Carrot seeds were planted on top of PLA mulches without planting holes and top-dressed with compost to a depth of 0.5 inches to aid germination and root establishment through the mulch membrane. All PLA mulches reduced weed emergence by >89% compared with the no-mulch, no-compost control, and weed suppression was not different between fertilizer-enriched PLA mulches and PLA-only mulches. There was no difference in plant available soil N among mulch types and the no-mulch controls between 4 and 32 d after planting. PLA-only mulch did not immobilize N, nor did the fertilizer-enriched mulch increase plant available N. PLA-only mulches reduced carrot yield by 26% compared with compost only treatments in 2022. Yield loss was due to reduced stand density following physical seed displacement from the mulch surface during compost application and heavy rainfall events before seedling establishment. In 2023, carrot yield was variable among mulch types but reduced by 40% when mulches were top-dressed with the mixed feedstock compost compared with yard waste compost and no-compost treatments. The mixed feedstock compost in 2023 had elevated ammonium (0.15%), and its phytotoxic effects reduced carrot stand density by 65%, which highlights the importance of compost quality in this modified planting system. Results from this study demonstrate feasibility for manufacturing and field application of a biobased mulch enriched with solid organic fertilizer, but fertilizer enrichment did not improve soil nutrient availability or yield under the conditions studied. Future research in lower fertility soils or crops with higher early season nutrient removal rates is needed to further explore the potential value of fertilizer-enriched mulch.

Intensifying cover crop (CC) management via fertilization and harvesting could be a strategy to enhance agroecosystem benefits of CCs. Fertilization may boost productivity in low-biomass producing CCs (e.g., winter CCs) and allow for biomass harvest to support livestock and other off-farm uses while still delivering other soil services. We studied the impact of winter rye (Secale cereale L.) CC fertilization (0, 50, and 100 kg N ha-1) and CC harvesting on aboveground and belowground CC biomass production, soil organic matter, soil nitrate, and crop yields under irrigated no-till corn (Zea mays L.)-soybean (Glycine max L.) in the western US Corn Belt for 5 years. Fertilization increased aboveground CC biomass production in 2 of the 5 years. Across both of those 2 years, CC biomass production increased by 0.68 Mg ha-1 under 50 kg N ha-1 and by 1.15 Mg ha-1 under 100 kg N ha-1 over no fertilization, indicating that the increase in biomass production with fertilization was relatively modest. CC harvesting increased biomass production by 0.36 Mg ha-1 in 2 of 5 years. Fertilization did not affect forage CC nutritive value parameters, although numerically these parameters tended to increase. Fertilization increased soil nitrate concentration by 29%-53% at some soil depth intervals in the 60-cm depth. Fertilization and harvesting did not affect CC root biomass production, soil organic matter concentration, or crop yields. Overall, N fertilization of winter rye CCs may not increase CC biomass production in most years in this temperate soil.

Rising irrigation demand and declining groundwater resources threaten the sustainability of irrigated maize production in Nebraska. Benchmarking farmers’ applied irrigation against optimal amounts offers insight into management performance and highlights opportunities for improvement. However, the few benchmarking studies conducted in Nebraska have often relied on simplified modeling assumptions to estimate optimal irrigation, potentially overestimating the magnitude of differences from actual practices and overlooking factors that influence farmers’ decisions. This study applied the DSSAT CERES-Maize model to determine optimal irrigation using multi-year data from the University of Nebraska-Lincoln’s Testing Ag Performance Solutions (UNL-TAPS) program. The model, calibrated for cultivar traits and site-specific conditions, demonstrated strong agreement between simulated and observed phenology and yield during validation (NRMSE < 5

Hybrid selection is one of the first and most critical decisions made in a farming operation, and corn (Zea mays L.) hybrids respond differently to management practices like seeding rates. Understanding the effect of hybrid selection and seeding rate on corn yield and economic return is increasingly relevant as we seek to enhance the rate of productivity and financial viability in farming systems. Research studies conducted in four Nebraska fields during the 2018 and 2019 growing seasons evaluated the effect of hybrids and seeding rates on corn yields and partial economic returns. Eight hybrids and five seeding rates were studied across eight environments. Half of the environments were irrigated, and half were rainfed. Environments, hybrids, and seeding rates directly affected corn yields and the subsequent partial economic returns. The selection of hybrids and optimum seeding rates best adapted to specific environmental conditions resulted in more productivity and profitability. The highest yield ceilings for the hybrids studied ranged from 227 to 254 bushels per acre (overall mean = 237) under a seeding rate range of 27,945 to 41,491 seeds per acre. The highest net returns for the studied hybrids ranged from $81 to $173 per acre (overall mean = $120) with seeding rates ranging from 26,264 to 33,737 seeds per acre. The estimated average optimum seeding rate for maximum yield was 34,424 seeds per acre and 27,881 seeds per acre for maximum net return. Hybrids with longer relative maturities grown with irrigation had higher yield and net return potential compared to shorter maturities grown under rainfed conditions.

Early soybean planting and cover crop adoption in the U.S. Midwest prompt investigation into the impact of these practices on weed community dynamics and best management practices. While previous research has explored different aspects of giant ragweed control, the specific integration among soil management practices, including cover crop adoption, soybean planting timing, and herbicide use, has not been thoroughly investigated. This study assessed the effects of soil management, soybean planting time, and preemergence (PRE) herbicide application on giant ragweed control and soybean yield in Wisconsin and Nebraska in 2022 and 2023. The study included a factorial arrangement of four soil management treatments (conventional tillage, no-till, and fall-planted cereal rye early terminated and terminated at planting [planting green]), two soybean planting times, and two PRE herbicide treatments (PRE and no PRE). POST herbicides were applied when similar to 50% of giant ragweed plants within each treatment reached similar to 10 cm in height. In Nebraska, cereal rye and tillage treatments without a PRE had at least 67% lower giant ragweed density than no-till at POST. In no-till, densities were at least 60% lower with PRE compared to no PRE. In Wisconsin, cereal rye did not reduce giant ragweed density at POST compared to no-till, likely due to relatively low biomass accumulation. In contrast, delayed soybean planting reduced giant ragweed density for most treatments but lowered soybean yield in no-till and planting-green treatments. The PRE herbicides had either no effect or positive effects on reducing giant ragweed density and increasing soybean yield. Overall, this study suggests that soil management and soybean planting timing are crucial for effective giant ragweed management in Wisconsin, where biotypes with a long emergence window during the spring and summer are present, while in Nebraska, soil management and soybean planting timing are less critical due to giant ragweed biotypes with an early and short emergence window in the spring.

Interseeding cover crops (CCs) may be a potential strategy to manage sandy soils, which are highly prone to degradation. However, how this practice affects CC biomass production and other ecosystem services in sandy soils over the traditional CC planting system (post-harvest drilling) is still unclear. We studied how broadcast interseeded (32-67 days before crop harvest) winter rye (Secale cereale L.) CC affected CC biomass production, nitrate leaching potential, soil properties, crop yields, and farm income compared with post-harvest drilled CC in an on-farm irrigated no-till corn (Zea mays L.)-soybean (Glycine max L.) experiment in a sandy loam in the western US Corn Belt for 6 years. Across the 6 years, interseeded CC produced 0.57 Mg ha-1 of biomass, while post-harvest drilled CC produced 0.37 Mg ha-1. Nitrate leaching is a concern in sandy soils, but interseeded CC had mixed effects on soil nitrate concentration. Interseeded CC did not affect soil properties (particulate organic matter and organic C concentrations, and wet aggregate stability) and crop yields. Further, interseeded CC did not reduce farm income more than post-harvest drilled CC. The limited effect of interseeded CCs is likely due to the relatively small increase in CC biomass production over the traditional CC planting system. Additional strategies including irrigation, drill interseeding, and planting green may boost interseeded CC biomass production and thus soil services in sandy soils. After 6 years, interseeded CC slightly boosted CC biomass production but minimally affected soils and crops, and both interseeded and post-harvest-drilled CCs reduced net income.

Increasing groundwater nitrate (NO3-N) contamination has raised significant environmental and health concerns in irrigated sandy soils of Nebraska. This study evaluated the effects of suboptimum nitrogen (N) and deficit irrigation rates on NOB-N leaching, crop yield, and economic returns to nitrogen, both with (RTNEnv) and without (RTN) accounting for environmental costs. The two-year on-farm study utilized a two-factor factorial design with three N rates (optimum, suboptimum, and low) and three irrigation rates (farmer's full irrigation [FIT], 80 % of FIT, and 60% of FIT) in continuous maize grown on irrigated sandy soils in the Bazile Groundwater Management Area, Nebraska. The results indicated that nitrogen rates had a greater impact on seasonal NOB-N leaching than irrigation rates. Compared to the optimum (270 kg N ha-1 ), the suboptimum (202 kg N ha-1 ) and low N rates (135 kg N ha-1 ) reduced NOB-N leaching by 24% (7 kg NOB-N ha-1 ) and 51 % (15 kg NOB-N ha-1 ), respectively. Maize yield decreased by 8% (14.5 Mg ha-1 ) and 11 % (14.0 Mg ha-1 ), while RTN dropped by $215 ha-1 and $298 ha-1 , respectively. Notably, reduced N rates did not affect RTNEnv. The 80% FIT treatment produced significantly higher grain yield and RTN but did not affect NOB-N leaching compared to both the 60 % FIT and FIT treatments. Additionally, inter-annual variability had a more pronounced effect on nitrate leaching than the treatments themselves. In 2021, NOB-N leaching was 64% lower due to 38% less irrigation, 37% higher grain N uptake, and 74% lower residual N-resulting in $214 more in RTN and $587 more in RTNEnv compared to 2022. In conclusion, findings suggest that reducing nitrogen rates is more effective in minimizing nitrate leaching than within-season irrigation reductions under current sprinkler irrigation practices. Additionally, inter-annual variability in NO3-N leaching should be considered when developing strategies to improve nitrogen management in groundwater contaminated areas.

Increasing groundwater nitrate (NO 3 ‐N) contamination in Nebraska's Bazile Groundwater Management Area poses significant economic, environmental, and public health risks. This 2‐year (2021–2022) on‐farm study evaluated the effects of nitrogen (N) application timing (preplant vs. split) and source (with and without enhanced efficiency fertilizers [EEFs], including urease inhibitor [UI] and dual inhibitor [DI] combining urease and nitrification inhibitor) on NO 3 ‐N leaching, maize yield, and return to N with environmental cost (RTN Env ) in irrigated sandy soils. Six N treatments at 202 kg N ha −1 were compared to a zero‐N control: preplant urea, conventional split urea‐UAN (urea ammonium nitrate), preplant UI, split UI‐UAN, preplant DI, and split DI‐UAN. Porous suction cup lysimeters were installed at a depth of 120 cm to collect pore‐water samples within the growing seasons. Compared to conventional split urea‐UAN, preplant EEFs (preplant UI and preplant DI) reduced nitrate leaching by 75% and increased RTN Env by $537 ha −1 without significantly affecting maize yield. Split EEFs (split UI‐UAN and split DI‐UAN) reduced NO 3 ‐N leaching by 31% and increased grain yield by 9.6% compared to preplant Urea in 2021. However, the split EEFs increased NO 3 ‐N leaching by 139% compared to the preplant EEF treatments, with no corresponding yield improvement. These findings suggest that preplant application of EEFs can substantially reduce NO 3 ‐N leaching without compromising maize yield while offering greater economic returns in areas affected by groundwater contamination.

Over the last several decades, the intensive production of corn (Zea mays L.) and soybeans (Glycine max L.) in the United States has included the widespread use of herbicide-tolerant crops, contributing to soil management with reduced tillage. The continuous use of herbicides with the same modes of action has led to the accelerated development of herbicide resistance in weed populations, particularly from the Amaranthaceae family. Integrated weed management tools, such as the use of cover crops, have increasingly been recognized as cultural approaches with the potential to reduce herbicide-driven selection pressure. We utilized six multi-year (4–7 years) cover crop research trials in corn-based crop rotations to measure germinable weed seedbanks, aboveground weed density, and biomass. This included four on-farm and two university research experiments across eastern and central Nebraska, with histories of no tillage or reduced tillage. Three sites showed increases in Amaranthaceae family (pigweed) seedbank densities under cover crops (137%–355%) compared to the no cover crop check, but no differences in total weed seed bank densities were found. Cover crops reduced aboveground total weed density and biomass at the two sites; however, increases from the pigweed seedbank were not observed at any site. Multivariate analyses revealed that the species composition of the seedbanks under cover crops was distinct from that of the check at the two sites, suggesting that cover crops may influence weed seedbank composition over time. This work underscores the value of exploring integrated weed management, as well as monitoring weed populations in the soil seedbank and aboveground emerged species, particularly in cropping systems with reduced soil disturbance. We encourage more research on the multi-year use of integrated weed management approaches, such as cover crops, to better understand the complexity of how such approaches shift weed communities, especially with respect to herbicide-resistant weeds.

Integrating water and nitrogen (N) management is critical to addressing contemporary challenges in agricultural development. This research explored using multispectral sensors mounted on unmanned aerial vehicles (UAVs) to monitor N demand via the normalized difference red-edge (NDRE) vegetation index and consequently schedule fertigation. The experiment included eight treatments with four fertilizer levels under both excessive and full irrigation. The four fertilizer levels comprised: high reference treatment based on commercial lab soil tests, sensor-based treatment triggered by an NDRE saturation threshold of 0.95, deficit treatment with base rate at pre-plant and side-dress, and a control treatment without any N application. The performance of each treatment was evaluated through a comprehensive comparison of yield, water productivity (WP), and nitrogen use efficiency (NUE). The sufficiency index (SI) of sensor-based treatment plots reached a threshold of 0.95, allowing spatially variable adjustment of N application for optimal yield with reduced total N input. Reducing N fertilizer in sensor-based treatments resulted in a substantial reduction of 50 %-60 %, though it led to a yield loss up to 12 %. However, NUE parameters such as partial factor productivity, agronomic efficiency, recovery efficiency, and physiological efficiency improved with sensor-based treatments, alongside reduced N leaching. Combining sensor-based treatment with full irrigation demonstrated the best ecological return, showing relatively lower yield reduction but significant improvements in NUE and WP. Further research into economic returns, saturation threshold algorithms for SI, adaptability to diverse environments, and virtual saturation reference is recommended for the widespread adoption of UAV-based N split management among growers.

AbstractLittle information is available on optimizing the number of nitrogen (N) splits based on nitrate (NO3‐N) leaching and maize yield in sandy soils. To address this gap, we evaluated the impact of multiple N splits (2‐, 3‐, 4‐, and 5‐N splits) on NO3‐N leaching and maize (Zea mays L.) grain yield in irrigated loamy sand soil at a producer site in the Bazile Groundwater Management Area of Northeast Nebraska. Porous suction cup lysimeters were installed at a depth of 120 cm to collect pore water samples from 23 leaching events in 2021, a dry year. Increasing the number of N‐splits did not affect the pore‐water NO3‐N concentration; however, it was 169%, 152%, 150%, and 129% higher in 2‐, 3‐, 4‐, and 5‐N split treatments compared to control, that is, without N application. Though the 2‐, 3‐, 4‐, and 5‐N splits had 110%, 71%, 120%, and 91% higher area‐based NO3‐N leaching than the control, less deep percolation and more evapotranspiration in control led to no significant differences in area‐based NO3‐N leaching among all treatments. All N‐splits resulted in higher maize yield, nitrogen use efficiency, plant N uptake, harvest index, and aboveground biomass than control; however, the number of N‐splits did not affect these parameters. The inclusion of environmental cost reduced the return to nitrogen by 92–143 $ ha−1 across all N‐split treatments but did not significantly affect the differences among the splits. Overall, the results indicate that increasing the number of N‐splits does not provide agronomic, economic, and environmental benefits in irrigated maize fields during a dry year.

Cover crop growing periods in the western U.S. Corn Belt could be extended by planting earlier. We evaluated both pre-harvest broadcast interseeding and post-harvest drilling of the following cover crops: (a) cereal rye (Secale cereale L.) [RYE]; (b) a mix of rye + legumes + brassicas [MIX1], (c) a mix of rye + oat [Avena sativa L.] + legumes + brassicas (MIX2), (d) legumes [LEGU]) and (e) a no cover crop control. These were tested in continuous corn (Zea mays L.) [corn-corn] and soybean [Glycine max (L.) Merr.]-corn systems [soybean-corn] at three sites in Nebraska for their effect on cover crop productivity, soil nutrients, and subsequent corn performance. At the sites with wet fall weather, pre-harvest broadcasting increased cover crop biomass by 90%, to 1.29 Mg ha(-1) for RYE and 0.87 Mg ha(-1) for MIX1 in soybean-corn, and to 0.56 Mg ha(-1) and 0.39 Mg ha(-1) in corn-corn, respectively. At the drier site, post-harvest drilling increased biomass of RYE and MIX1 by 95% to 0.80 Mg ha(-1) in soybean-corn. Biomass N uptake was highest in pre-harvest RYE and MIX1 at two sites in soybean-corn (35 kg ha(-1)). RYE and sometimes mixes reduced soil N, but effects on P, K, and soil organic C were inconsistent. In soybean-corn, corn yields decreased by 4% after RYE, and in corn-corn, by 4% after pre-harvest cover crops. Site-specific selection of cover crops and planting practices can increase their performance while minimizing impacts on corn.

Duration of cover crop (CC) management, CC biomass production, and other factors could impact how CC affects soil health. We studied the 8-year cumulative impacts of winter rye (Secale cereale L.) CC on soil physical, chemical, and biological properties in rainfed and irrigated no-till corn (Zea mays L.)-based systems in the western US Corn Belt. Average annual CC biomass production was 0.56 & PLUSMN; 0.51 Mg ha(-1) at the rainfed site and 0.98 & PLUSMN; 0.95 Mg ha(-1) at the irrigated site. After 8 years, CC improved particulate organic matter (POM) and mean weight diameter of water-stable aggregates (MWD) compared with no CC in the 0-5 cm soil depth at both sites. Cover crop increased total POM concentration by 2.8 mg g(-1) at the rainfed site and by 13.4 mg g(-1) at the irrigated site, while it increased MWD by 0.39 mm at the rainfed site and by 0.79 mm at the irrigated site. Also, CC increased soil C at a rate of 0.125 Mg ha(-1) year(-1) in the 0-5 cm depth but only at the rainfed site. Cover crop affected neither water infiltration nor available water but improved microbial biomass. Changes in other properties were site-dependent. Cover crop improved many soil properties after 8 years even though measurement taken after 4 years showed no significant effect of CC, which indicates CC slowly impacts properties in this environment. Low CC biomass production and high biomass input from corn-based systems may explain the slow soil response. In general, winter rye CC enhances near-surface soil properties in the long term.

Context or problem: A trade-off between seed protein concentration (SPC) and yield has been reported for soybean. Therefore, assessing management practices that can nullify this trade-off is relevant to avoid further declines in SPC in the future as yield continues to increase. While the positive effect of irrigation on yield is well documented, only a few studies have assessed the impact of irrigation on SPC, showing conflicting results.Objective or research question: The objective was to determine if the trade-off between seed yield and SPC persists when irrigation is applied and how management, soil, and weather factors influence the trade-off. We hypothesized that yield increases induced by irrigation would likely decrease SPC.Methods: Our experimental approach involved the use of producer-reported data, in-situ seed collection, and crop modeling. Yield and management data were collected from 268 soybean fields in Nebraska (USA), along with data on SPC, seed oil concentration (SOC), and seed carbohydrate concentration (SCC) determined from samples collected in each field. Field-specific phenological data were derived from model simulations. The combined data were then used to assess the effect of irrigation on seed yield and constituents as influenced by management, soil, and weather factors.Results: On average, both seed yield (+0.86 Mg ha-1) and SPC (+3.2 g kg-1) were higher, but SOC (-2.0 g kg-1) was lower, and SCC was unaffected in irrigated versus rainfed field pairs. Yield and SPC increased simultaneously in response to irrigation in two-thirds of the fields, especially when environmental conditions did not favor seed oil synthesis (e.g., cooler temperature and less incident solar radiation). A trade-off of higher seed yield and lower SPC occurred with irrigation in the remaining fields wherein conditions were favorable for seed oil synthesis (e. g., warmer temperatures and greater radiation).Conclusions: Despite higher seed yield generated in irrigated versus rainfed fields, no concurrent reduction occurred in SPC in the majority of irrigated fields - a surprising finding that was not consistent with the general expectation that higher soybean yields typically result in yield-SPC trade-off. Implications or significance: This study showed that irrigation-induced higher soybean yields are possible without an attendant SPC penalty when temperatures and radiation are conducive for its mitigation. We are unaware of any other yield-increasing practices - except nitrogen (N) fertilization -that do not result in a concomitant decline in SPC. A hypothesized higher N supply via soil N mineralization and/or biological N fixation in irrigated fields in this study may explain the absence of yield-protein trade-off.

Relative to fallow-cash crop rotations, the addition of a cover crop can contribute to greater plant diversity and has the potential to conserve predatory arthropods. The transition of arthropods from a cover crop to a subsequent cash crop depends on several factors, such as cover crop biomass production and weather conditions. Information about the effect of cover crop planting and termination dates on arthropods in a subsequent corn system is limited. A two-year field study was conducted in Nebraska in 2018/2019 and 2019/2020 to evaluate the impact of cover crop planting and termination dates as a source for arthropods in the subsequent corn. A total of 38,074 and 50,626 arthropods were collected in the first and second year, respectively. In both years, adding a grass cover crop increased predatory arthropods but reduced yield in follow corn crop. Of the arthropods collected, Carabidae and Araneae had greater activity with cover crop biomass increments, whereas Collembola and Acari activity only increased in treatments with little or no cover crop biomass. Insect pest pressure was not significant in any treatment for either year. A cover crop planted in mid- or late-September and terminated at corn planting was identified as the best management strategy to maximize cover crop biomass, increase predator activity, and modify predator-prey dynamics. The results of this study provide growers with a cover crop management strategy to maximize cover crop biomass, beneficial arthropod activity, and potentially minimize insect pest problems; however, corn Zea Mays (L.) grain yield was reduced as cover crop biomass increased.

Horseweed is a North American indigenous plant species commonly found in Nebraska cropping systems. Horseweed management is challenging because of horseweed's prolific seed production, long-distance seed dispersal via wind, competitiveness, and rapid evolution of herbicide resistance. Understanding the horseweed emergence pattern across Nebraska can contribute to implementing effective and more sustainable tactics to minimize its impact on cropping systems. Field studies were conducted during fall and spring from 2016 to 2018 in Lincoln (corn and soybean), North Platte (wheat stubble and soybean), and Scottsbluff (corn and fallow) to investigate the emergence pattern of horseweed accessions from Lincoln, North Platte, and Scottsbluff, NE. Results show that most horseweed seedling emergence occurred in fall (99%) and only a few seedlings emerged in spring across locations, except in the wheat stubble experiment at North Platte, where higher spring emergence was detected (3% to 22%). In four out of six experiments, the density of total emerged seedlings of each accession was greatest when established in their site of origin. Our results suggest that late fall and/or early spring is likely the best timing for horseweed management across Nebraska.

Soybean [Glycine max (L.) Moench.] yield is determined by interactions amongst soybean cultivars' genetic potential, agronomic practices, and environmental conditions. Despite the high adoption of herbicide-resistant soybean cultivars across Nebraska and the United States, the comparative yield potential of non-herbicide-resistant ("conventional") cultivars in not well understood. A field experiment was conducted at five locations across Nebraska in 2017 and 2018 to determine the effect of row spacing (15 and 30 in), cultivar maturity group (2.2-2.4 and 3.2), and herbicide resistance traits (conventional, glyphosate-resistant, and glyphosate- and dicamba-resistant) on soybean yield. Narrow row spacing increased the soybean yield in three of five research locations. The soybean yield in Auburn in 2017, Albion in 2018, and Cedar Bluffs in 2018 increased by 11.9, 10.2, and 11.4% in narrow compared with wide rows, respectively. Cultivar maturity group and herbicide resistance traits did not affect soybean yield under weed-free experimental conditions. These results suggest that growers could benefit from earlier maturity groups, as they provide an opportunity for earlier harvest, allowing growers to better spread their field activities in the fall. The grain yield potential was similar between conventional and transgenic herbicide-resistant cultivars. Therefore, conventional soybean cultivars can be a viable option when adequate weed management can be achieved through conventional weed management strategies.

Palmer amaranth (Amaranthus palmeri S. Watson) is one of the most troublesome agronomic weed species in the United States. Palmer amaranth is prevalent in the Southern Great Plains and the Southeastern United States, and its range is expanding northward through natural dispersal and human intervention. Palmer amaranth dispersal warrants studies assessing species adaptation into new geographies. A study was conducted in 2018 and 2019 to investigate the morphology, flowering, and gender from cohorts of Palmer amaranth growing under corn, soybean, and bareground across five locations in the Midwest United States. Results demonstrated that the first cohort of Palmer amaranth, established in June, produced 42% more biomass than plants from the second cohort (established in July). The first Palmer amaranth cohort produced 75.5 g plant(-1) in bareground, 28.3 g plant(-1) in soybean, and 16.3 g plant(-1) in corn, whereas the second Palmer amaranth cohort produced 62.6, 6.3, and 1.4 g plant(-1) in bareground, soybean, and corn, respectively. Palmer amaranth height was most impacted when growing in corn and averaged 85.2 cm tall in the first cohort, and 38.2 cm tall in the second cohort in corn. Moreover, Palmer amaranth flowering window shifted according to crop and cohort timings. Palmer amaranth growing in intense competition, such as under low light in corn, resulted in the longest flowering window. Palmer amaranth gender was slightly influenced by day of year, weight, and height. We documented a high degree of plasticity in Palmer amaranth, which will presumably favor its adaptation and expansion in cropping systems north of its current range. Therefore, preventing Palmer amaranth dispersal into new habitats is the most effective management strategy.

Herbicides with soil-residual activity have the potential for carryover into subsequent crops, resulting in injury to sensitive crops and limiting productivity if severe. The increased use of soil-residual herbicides in the United States for management of troublesome weeds in corn- and soybean-cropping systems has potential to result in more cases of carryover. Soil management practices have different effects on the soil environment, potentially influencing herbicide degradation and likelihood of carryover. Field experiments were conducted at three sites in 2019 and 2020 to determine the effects of corn (clopyralid and mesotrione) and soybean (fomesafen and imazethapyr) herbicides applied in the fall at reduced rates (25% and 50% of labeled rates) and three soil management practices (tillage, no-tillage, and a fall-established cereal rye cover crop) on subsequent growth and productivity of the cereal rye cover crop and the soybean and corn crops, respectively. Most response variables (cereal rye biomass and crop canopy cover at cover crop termination in the spring, early-season crop stand and herbicide injury ratings, and crop yield) were not affected by herbicide carryover. Corn yield was lower when soil was managed with a cereal rye cover crop compared with tillage at all three sites, while yield was lower for no-till compared with tillage at two sites. Soybean yield was lower when managed with a cereal rye cover crop compared with tillage and no-till at one site. Findings from this research indicate a low carryover risk for these herbicides across site-years when label rotational restrictions are followed and environmental conditions favorable for herbicide degradation exist, regardless of soil management practice on silt loam or silty clay loam soil types in the U.S. Midwest region.

While herbicides provided an opportunity to expand many important soil conservation practices, overuse of glyphosate and the evolution of glyphosateresistant weeds poses one the greatest threats to conservation tillage as it has forced some farmers to revert to conventional tillage for effective weed control. Cover crops have the potential to delay weed emergence, decrease weed size, and decrease weed number. However, the beneficial gains in cover crop–related weed suppression should be considered against the potential trade-offs with cropping system productivity. This article is the first in the three-part series in Crops & Soils magazine. It is part of an American Society of Agronomy training series sponsored by the Kellogg Company. Earn 0.5 CEUs in Integrated Pest Management by reading this article and taking the quiz at www.certifiedcropadviser.org/ education/classroom/classes/941.