Auxin-based Herbicide Program for Weed Control in Auxin Resistant Soybean

Soybean [Glycine max (L.) Merr.] cultivars resistant to synthetic auxin herbicides have provided another mode of action for the postemergence broadleaf weed control. This field study was conducted at three South Dakota locations [Northeast, NERF; east-central, ARF; and Southeast, SERF) in 2019 and two locations (ARF and SERF) in 2020. The Enlist E3 and Roundup Ready 2 Xtend cultivars were planted at three dates (early, mid-, and late season) to examine weed control, agronomic characteristics, nodulation, and yield. Preemergence (PRE) treatment was flumioxazin + metribuzin + S-metolachlor + glyphosate + pendimethalin. Two postemergence (POST) treatments, based on cultivar, were compared with PRE-only. The PREonly treatment had numerous grasses {including green foxtail [Setaria viridis (L.) P. Beauv.] and yellow foxtail [S. pumila (Poir.) Roem. & Schult.], volunteer corn (Zea mays L.), barnyard grass [Echinochola crus-galli (L.) Beauv.], large crabgrass [Digitaria sanguinalis (L.) Scop.], woolly cupgrass [Eriochloa villosa (Thunb.) Kunth]} and broadleaf weeds (including redroot pigweed [Amaranthus retroflexus L.], common lambsquarters [Chenopodium album L.], waterhemp [Amaranthus rudis Sauer]) with high density and biomass. POST treatments controlled most of the broadleaf species, although some grasses remained. Yields were similar within a location and year, although differences occurred among planting dates. In 2019, planting date did not influence final yield at ARF (average yield 3,084 kg ha−1). Yield was greatest for the early (NERF) and mid-planting dates (NERF and SERF) compared with late-season planting. In 2020, dry conditions occurred, and yields at ARF and SERF were lowest for the late-season plantings (ranging from 37 to 73% lower depending on cultivar) compared with the early season planting. In 2020, dicamba + glyphosate treatment of the Xtend cultivar had 10% (ARF) and 20% (SERF) greater yield than the acifluorfen + clethodim treatment

Quantification and Machine Learning Based N2O-N and CO2-C Emissions Predictions from a Decomposing Rye Cover Crop

Cover crops improve soil health and reduce the risk of soil erosion. However, their impact on the carbon dioxide equivalence (CO2e) is unknown. Therefore, objective of this two-year study was to quantify the effect of cover crop-induced differences in soil moisture, temperature, organic C, and microorganisms on CO2e and to develop machine learning algorithms that predict daily N2O-N and CO2-C emissions. The prediction models tested were multiple linear regression (MLR), partial least square regression (PLSR), support vector machine (SVM), random forest (RF), and artificial neural network (ANN). Models’ performance was accessed using R2 , RMSE and MAE. Rye (secale cereale) was dormant seeded in mid-October and in the following spring it was terminated at corn’s (Zea mays) V4 growth stage. Soil temperature, moisture, and N2O-N and CO2-C emissions were measured near continuously from soil thaw to harvest in 2019 and 2020. Prior to termination, the cover crop decreased N2O-N emissions by 34% (p=0.05) and over the entire season, N2O-N emissions from cover crop and no cover crop treatments were similar (p=0.71). Based on N2O-N and CO2-C emissions over the entire season and the estimated fixed cover crop carbon remaining in the soil, the partial CO2e were -1,061 and 496 kg CO2e ha-1 in the cover crop and no cover crop treatments, respectively. The RF algorithm explained more of the daily N2O-N (73%) and CO2-C (85%) emissions variability during validation than the other models. Across models, the most important variables were temperature and the amount of cover crop-C added to the soil

Winter Cereal Rye Cover Crop Decreased Nitrous Oxide Emissions During Early Spring

Despite differences between the cover crop growth and decomposition phases, few greenhouse gas (GHG) studies have separated these phases from each other. This study’s hypothesis was that a living cover crop reduces soil inorganic N concentrations and soil water, thereby reducing N2O emissions. We quantified the effects of a fall-planted living cereal rye (Secale cereale L.) cover crop (2017, 2018, 2019) on the following spring’s soil temperature, soil water, water-filled porosity (WFP), inorganic N, and GHG (N2O-N and CO2–C) emissions and compared these measurements to bare soil. The experimental design was a randomized complete block, where years were treated as blocks. Rye was fall planted in 2017, 2018, and 2019, but mostly emerged the following spring. The GHG emissions were near-continuously measured from early spring through June. Rye biomass was 1,049, 428, and 2,647 kg ha–1 in 2018, 2019, and 2020, respectively. Compared to the bare soil, rye reduced WFP in the surface 5 cm by 29, 15, and 26% in 2018, 2019, and 2020 and reduced soil NO3–N in surface 30 cm by 53% in 2019 (p = .04) and 65% in 2020 (p = .07), respectively. Rye changed the N2O and CO2 frequency emission signatures. It also reduced N2O emissions by 66% but did not influence CO2–C emissions during the period prior to corn (Zea mays L.) emergence (VE). After VE, rye and bare soils N2O emissions were similar. These results suggest that nitrous oxide (N2O-N) sampling protocols must account for early season impacts of the living cover

Weed Presence Altered Biotic Stress and Light Signaling in Maize Even When Weeds were Removed Early in the Critical Weed‐free Period

Weed presence early in the life cycle of maize (typically, from emergence through the 8 to 12 leaf growth stage) can reduce crop growth and yield and is known as the critical weed‐free period (CWFP). Even if weeds are removed during or just after the CWFP, crop growth and yield often are not recoverable. We compared transcriptome responses of field‐grown hybrid maize at V8 in two consecutive years among plants grown under weed‐free and two weed‐stressed conditions (weeds removed at V4 or present through V8) using RNAseq analysis techniques. Compared with weed‐free plant responses, physiological differences at V8 were identified in all weed‐stressed plants and were most often associated with altered photosynthetic processes, hormone signaling, nitrogen use and transport, and biotic stress responses. Even when weeds were removed at V4 and tissues sampled at V8, carbon: nitrogen supply imbalance, salicylic acid signals, and growth responses differed between the weed‐stressed and weed‐free plants. These underlying processes and a small number of developmentally important genes are potential targets for decreasing the maize response to weed pressure. Expression differences of several novel, long noncoding RNAs resulting from exposure of maize to weeds during the CWFP were also observed and could open new avenues for investigation into the function of these transcription units

Examining the Role of Marine Mammals and Seabirds in Southeast Alaska’s Marine Ecosystem Dynamics

Primary producers are the foundation of marine food webs and require reliable nutrient sources to maintain their important role with ecosystems. While marine mammals and seabirds can play critical roles in marine nutrient cycling, their contributions are often overlooked. The fjord systems of Southeast Alaska support a high diversity of marine mammals and seabirds in addition to some of the most valuable fisheries in the US. Nonetheless, there is still relatively little known about nutrient sources and fluxes in this region which is a critical component of fisheries management. The goal of our study was to advance knowledge of the role of mammals and seabirds in marine nutrient cycling and to understand how changing marine mammal and seabird populations may alter ecosystem dynamics. We analyzed nutrient levels in marine mammal scat, seabird guano, and seawater samples collected in Berners Bay, Southeast Alaska, to determine the influence of marine mammals and seabirds on nearshore nutrient concentrations. Utilizing qualitative network models (QNMs), we then examined how a simulated Berners Bay ecosystem would respond to an increase in marine mammals, seabirds, and nutrients. Researchers are increasingly utilizing QNMs as a first step in the development of ecosystem-based fisheries management plans as their adaptable nature is well suited to address rapidly changing climatic conditions. Our direct nutrient measurements and QNM results indicate that marine mammals and seabirds have the potential to provide substantial contributions to marine nutrient concentrations in the region and that these valuable ecosystem services should not be overlooked.We sincerely thank the reviewers for their suggestions and feedbackYe

Rye Cover Crop Termination Timing Influenced Early Corn Growth, Gene Expressions, And Yield in a No-Till System

Cover crops provide soil health benefits to crop production. However, spring termination timing must be critically managed to prevent crop competition and yield loss. This study examined the influence of termination timing of fall-seeded rye (Secale cereale) on early corn (Zea mays) growth, gene expressions, and yield. Treatments included no cover crop, rye termination before corn planting, at corn planting, at V2, and at V4 corn. Rye was drill-seeded at 56 kg ha-1 in October 2018 and 2019. Corn was planted in mid-May 2019 (wet season) and 2020 (dry season). Rye biomass was 21 (2019) or 28 (2020) kg ha-1, 75 (2019) or 62 (2020) kg ha-1, 722 (2019) or 634 (2020) kg ha-1, and 1,120 (2019) or 702 (2020) kg ha-1 at before corn planting, corn planting, V2, and V4 rye termination, respectively. Transcriptome analysis of V4 samples in rye termination at V4 versus no cover crop resulted: 1) reduced corn growth and plant tissue nitrogen in both years; 2) 25 differentially expressed genes (DEGs) in 2019 and 322 (13X more) in 2020; 3) upregulated N metabolism ontology in 2019; and d) upregulated photosynthesis, carbon fixation and light signaling ontologies in 2020. Also, significant pathways including photosynthesis, carbon fixation in photosynthetic organisms, and carbon metabolism were altered regardless of climate conditions at V4 rye termination and can be attributed to corn-rye interactions. In V8 (2019) samples, response to cold and response to abscisic acid were upregulated, whereas photosynthesis and protein transport were downregulated at V4 rye termination versus no cover crop. In 2019, yield loss (16%) did not occur until V4 rye termination versus no cover crop. In 2020, yield was 19, 29, and 38% less when rye was terminated at corn planting, V2, and V4, respectively. This study suggests that during a wet season, delaying rye termination time until V2 may alter specific DEGs and pathways, but can provide more rye biomass without reducing corn yield. Inversely, during a dry season, delaying termination until planting or beyond can negatively impact corn development and significantly reduce corn yield

Effectiveness of Control Treatments on Young Saitcedar (Tamarix spp.) Plants

Preventing the establishment of saltcedar in new areas requires early detection and rapid response. However, it is unclear when saltcedar develops perennating tissue and which treatments are most efficacious for young plants. The effectiveness of mowing, herbicide, and fire treatments, alone and in combination, was evaluated on saltcedar plants grown from seed to 4, 8, and 12 wk age in 2011 and 6 and 12 wk age in 2012. Plants were clipped to 2 cm height or remained intact. Plants were then exposed to no treatment (control), herbicide application (0.12 mg ae imazapyr), or treated with fire for 30 or 60 s. Six weeks after treatment, plant survival and tallest living shoot height were recorded and roots were dried and weighed for biomass comparison. Saltcedar survival increased with greater plant age. No 4-wk-old plants survived herbicide or fire treatments, whereas 6-wk-old plants were eliminated by fire. Clipping alone did not control plants of any age but clipping before fire was the most effective control for older plants. Herbicide alone did not kill 8- and 12-wk-old plants during the study period, but reduced plant vigor suggests that these applications may be effective in the long-term. Fire alone for 60 s was the most effective single treatment for 12-wk-old plants. Root biomass was reduced for all treatments relative to untreated plants with the lowest biomass typically associated with fire treatments. Resprouts were shortest for combined clipping and herbicide and clipping and fire treatments. Results indicate that saltcedar grown from seed can develop viable belowground reproductive tissues between 6 and 8 wk after germination. Multiple intensive control practices may be required to kill saltcedar plants ≥8 wk of age, whereas younger plants can be controlled by single, less-intensive treatments such as fire

Tillage and Corn Residue Harvesting Impact Surface and Subsurface Carbon Sequestration

Corn stover harvesting is a common practice in the western U.S. Corn Belt. This 5-yr study used isotopic source tracking to quantify the influence of two tillage systems, two corn (Zea mays L.) surface residue removal rates, and two yield zones on soil organic C (SOC) gains and losses at three soil depths. Soil samples collected in 2008 and 2012 were used to determine 13C enrichment during SOC mineralization, the amount of initial SOC mineralized (SOClost), and plant C retained in the soil (PCRincorp) and sequestered C (PCRincorp − SOClost). The 30% residue soil cover after planting was achieved by the no-till and residue returned treatments and was not achieved by the chisel plow, residue removed treatment. In the 0- to 15-cm soil depth, the high yield zone had lower SOCloss (1.49 Mg ha−1) than the moderate yield zone (2.18 Mg ha−1), whereas in the 15- to 30-cm soil depth, SOCloss was higher in the 60% (1.38 Mg ha−1) than the 0% (0.82 Mg ha−1) residue removal treatment. When the 0- to 15- and 15- to 30-cm soil depths were combined, (i) 0.91 and 3.62 Mg SOC ha−1 were sequestered in the 60 and 0% residue removal treatments; (ii) 2.51 and 0.36 Mg SOC ha−1 were sequestered in the no-till and chisel plow treatments, and (iii) 1.16 and 1.65 Mg SOC ha−1 were sequestered in the moderate and high yield zone treatments, respectively. The surface treatments influenced C cycling in the 0- to 15- and 15- to 30-cm depths but did not influence SOC turnover in the 30- to 60-cm depth

RNAseq reveals weed-induced PIF3-like as a candidate target to manipulate weed stress response in soybean

Weeds reduce yield in soybeans (Glycine max) through incompletely defined mechanisms. The effects of weeds on the soybean transcriptome were evaluated in field conditions during four separate growing seasons. RNASeq data were collected from six biological samples of soybeans growing with or without weeds. Weed species and the methods to maintain weed-free controls varied between years to mitigate treatment effects, and to allow detection of general soybean weed responses. Soybean plants were not visibly nutrient- or water-stressed. We identified 55 consistently downregulated genes in weedy plots. Many of the downregulated genes were heat shock genes. Fourteen genes were consistently upregulated. Several transcription factors including a PHYTOCHROME INTERACTING FACTOR 3-like gene (PIF3) were included among the upregulated genes. Gene set enrichment analysis indicated roles for increased oxidative stress and jasmonic acid signaling responses during weed stress. The relationship of this weed-induced PIF3 gene to genes involved in shade avoidance responses in Arabidopsis provide evidence that this gene may be important in the response of soybean to weeds. These results suggest that the weed-induced PIF3 gene will be a target for manipulating weed tolerance in soybean