'Raising the bar' : improving the standard and utility of weed and invasive plant research

Fil: Murray, Justine V.. Water for Healthy Country Flagship; AustraliaFil: Lehnhoff, Erik A.. Montana State University; Estados UnidosFil: Neve, Paul. University of Warwick; Reino UnidoFil: Poggio, Santiago Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Webber, Bruce L.. CSIRO Ecosystems Sciences; Australia. The University of Western Australia; Australi

Timing Termination of a Biofumigant Cover Crop for Weed Suppression in Chile Pepper

Overwinter mustard cover crops incorporated into soil may suppress early-season weeds in chile pepper (Capsicum annuum). However, the potential for mustard cover crops to harbor beet leafhoppers (Circulifer tenellus) is a concern because beet leafhoppers transmit beet curly top virus to chile pepper. The objectives of this study were to determine the amounts of a biopesticidal compound (sinigrin) added to soil from ‘Caliente Rojo’ brown mustard (Brassica juncea) cover crops ended on three different days before beet leafhopper flights during spring and to determine the effects of the cover crop termination date on weed densities and hand-hoeing times for chile pepper. To address these objectives, a field study was conducted in southern New Mexico. In 2019–20, the cover crop was ended and incorporated into soil 45, 31, and 17 days before beet leafhopper flights. In 2020–21, cover crop termination occurred 36, 22, and 8 days before beet leafhopper flights. Treatments also included a no cover crop control. Cover crop biomass and sinigrin concentrations were determined at each termination. Chile pepper was seeded 28 days after the third termination date. Weed densities and hand-hoeing times were determined 28 and 56 days after chile pepper seeding. In 2019–20, the third termination (17 days before beet leafhopper flights) yielded the maximum cover crop biomass (820 g⋅m−2) and greatest sinigrin addition to soil (274 mmol⋅m−2). However, only the second termination (31 days before beet leafhopper flights) suppressed weeds in chile pepper. In 2020–21, the third termination (8 days before beet leafhopper flights) yielded the maximum cover crop biomass (591 g⋅m−2) and greatest sinigrin addition to soil (213 mmol⋅m−2), and it was the only treatment that suppressed weeds. No cover crop treatment reduced hand-hoeing times. These results indicate that overwinter mustard cover crops can be ended to evade beet leafhopper flights and suppress weeds in chile pepper

Invasiveness of yellow toadflax (Linaria vulgaris) resulting from disturbance and environmental conditions

Invasive plant species are considered to be one of the greatest threats to ecosystems and biological diversity throughout the world, and are thus often aggressively managed. The degree of plant invasiveness, however, varies both with environment and with type of landscape disturbance. This research was designed to understand how the factors of environment and disturbance affect the invasiveness of Linaria vulgaris (yellow toadflax) in southwest Montana and to quantify the varying degrees of invasiveness resulting from each factor. Data were obtained through four separate projects. The effects of disturbance size and propagule pressure on L. vulgaris establishment were evaluated through a series of experiments in both disturbed and undisturbed plots. L. vulgaris establishment and survival were low in all plots, but followed the general trend of more successful establishment in larger disturbed plots and in disturbed plots with a higher seeding density. An invasiveness index was developed that quantified invasiveness between -4 and +4 based on changes in population density and plant occupancy within permanent monitoring grids. This index was applied to L. vulgaris populations in three distinct environments, and invasiveness was found to range from -1.9 (declining population) to 1.8 (invasive population), indicating that invasiveness varied widely based on environment. The effects of the disturbances of herbicide, digging, burning and vegetation clipping on established L. vulgaris populations were evaluated in four environments. In the first year after treatment, herbicide reduced invasiveness of L. vulgaris in all environments, while digging and burning increased invasiveness and clipping had no effect. In the second year, herbicide resulted in increased L. vulgaris invasiveness at the three sites dominated by forbs, while it still reduced invasiveness at the grass-dominated site. The other treatments had minimal effects. Finally, effects of the above disturbances on the whole plant community were assessed using relative species abundance, richness and diversity metrics. Treatments generally decreased these metrics initially, but values recovered over time, with the exception of the herbicide treatment. The results demonstrated that L. vulgaris population invasiveness and treatment effectiveness varies with environment, suggesting that prioritizing management on an environment basis may be appropriate

Invasive plant benefits a native plant through plant-soil feedback but remains the superior competitor

Plant soil feedback (PSF) occurs when a plant modifies soil biotic properties and those changes in turn influence plant growth, survival or reproduction. These feedback effects are not well understood as mechanisms for invasive plant species. Eragrostis lehmanniana is an invasive species that has extensively colonized the southwest US. To address how PSFs may affect E. lehmanniana invasion and native Bouteloua gracilis growth, soil inoculant from four sites of known invasion age at the Appleton-Whittell Audubon Research Ranch in Sonoita, AZ were used in a PSF greenhouse study, incorporating a replacement series design. The purpose of this research was to evaluate PSF conspecific and heterospecific effects and competition outcomes between the invasive E. lehmanniana and a native forage grass, Bouteloua gracilis. Eragrostis lehmanniana PSFs were beneficial to B. gracilis if developed in previously invaded soil. Plant-soil feedback contributed to competitive suppression of B. gracilis only in the highest ratio of E. lehmanniana to B. gracilis. Plant-soil feedback did not provide an advantage to E. lehmanniana in competitive interactions with B. gracilis at low competition levels but were advantageous to E. lehmanniana at the highest competition ratio, indicating a possible density-dependent effect. Despite being beneficial to B. gracilis under many conditions, E. lehmanniana was the superior competitor

Cover Crops Enhance Soil Properties in Arid Agroecosystem despite Limited Irrigation

Cover crops (CCs) can enhance the sustainability and resiliency of agroecosystems by providing multiple ecosystem benefits, including soil quality improvement. However, in areas with limited precipitation such as the southwestern USA, cover cropping is challenging. With limited water, it may be difficult to raise cover crops for realizing ecosystem benefits. Research was conducted at two sites in New Mexico over two years to determine if CC under limited irrigation could produce enough biomass to improve soil quality. Treatments included a fallow (control) and monocultures of barley (Hordeum vulgare), Austrian winter peas (Pisum sativum subsp. arvense), mustard (Brassica rapa, var. Caliente 199), and a three-way mixture of these species, grown under three different irrigation regimes. The results indicate that the improvement in soil quality measurements by CCs grown under one supplemental irrigation were comparable to those grown under multiple irrigations. All CC treatments improved the soil dry aggregate size distribution from 2018 to 2020. At the end of the study, the MWD of dry aggregates was higher (3.26 mm) in all CC treatments than in the fallows (2.43 mm) at one site, but at the second site, mustard and mix were comparable to the fallows. Wet aggregate stability increased by 19% in the mix between 2018 and 2020 at one site. Pea plots needed about 23 kg ha−1 less N fertilizer for sweet corn production compared to the fallow treatment at one site. This suggests that CCs can be successfully grown under limited water availability in irrigated arid systems of New Mexico while still improving the soil quality

Impacts of Tamarix (L.) Litter and Mycorrhizal Amendments on Baccharis salicifolia (Ruiz & Pav.) Pers. Competitiveness and Mycorrhizal Colonization

Tamarix spp. are ecological threats in the Southwest U.S.A. because they displace native vegetation, increase soil salinity, and negatively affect soil microbial communities. After Tamarix L. removal, legacy effects often necessitate restoration to improve ecosystem services of Tamarix-impacted communities. Commercial mycorrhizae fungal inoculation has been recommended to improve restoration success, although inoculation treatments are rarely tested on lesser-known facultative riparian species. Our study asked two questions: (1) Can a commercial mycorrhizal fungal inoculant increase native Baccharis salicifolia (Ruiz & Pav.) Pers. (mule-fat) performance against Tamarix chinensis Lour. (i.e., tamarisk) and is this influenced by tamarisk leaf litter? (2) Is mycorrhizal colonization of mule-fat roots influenced by tamarisk stem density and leaf litter? A greenhouse experiment was performed with mule-fat cuttings in soil collected from a tamarisk monoculture. Treatments were factorial combinations of tamarisk stem densities (0, 1, 2, 3, 4 stems pot−1) with or without mycorrhizal inoculation and tamarisk litter. There were five replications and two greenhouse runs. The total biomass of both species was determined and mule-fat arbuscular mycorrhizal colonization rates were determined via the magnified intersection method. Increasing tamarisk biomass negatively affected mule-fat biomass, but there were interactions with tamarisk biomass, litter and mycorrhizal inoculation, with litter and inoculation increasing mule-fat growth at high tamarisk biomass. Arbuscular mycorrhizal colonization was high in all treatments, yet at higher tamarisk stem densities, inoculation and litter improved colonization. Interestingly, litter did not negatively impact mule-fat as predicted. Moreover, litter and mycorrhizal inoculum interacted with tamarisk to improve mule-fat growth at higher tamarisk biomass, suggesting an opportunity to improve restoration success when in competition with tamarisk

Organic Agriculture and the Quest for the Holy Grail in Water-Limited Ecosystems: Managing Weeds and Reducing Tillage Intensity

Organic agricultural production has become a major economic and cultural force. However, in water-limited environments the tools used for weed control and nutrient supply, namely tillage and cover crops, may not be environmentally or economically sustainable as tillage damages soil and cover crops use valuable water. Thus, a major challenge has been finding appropriate ways to minimize tillage and terminate cover crops while still controlling weeds and obtaining cover crop ecosystem services. One approach to achieve this is through the economically viable integration of crop and livestock enterprises to manage weeds and terminate cover crops. In this article we (1) review research needs and knowledge gaps in organic agriculture with special focus on water-limited environments; (2) summarize research aimed at developing no-till and reduced tillage in organic settings; (3) assess approaches to integrate crop and livestock production in organic systems; and (4) present initial results from a project assessing the agronomic and weed management challenges of integrated crop-livestock organic systems aimed at reducing tillage intensity in a water-limited environment. The goal of eliminating tillage in water-limited environments remains elusive, and more research is needed to successfully integrate tactics, such as cover crops and livestock grazing to increase organic farm sustainability

Heavy Metal Contamination in Agricultural Soil : Environmental Pollutants Affecting Crop Health

Heavy metals and metalloids (HMs) are environmental pollutants, most notably cadmium, lead, arsenic, mercury, and chromium. When HMs accumulate to toxic levels in agricultural soils, these non-biodegradable elements adversely affect crop health and productivity. The toxicity of HMs on crops depends upon factors including crop type, growth condition, and developmental stage; nature of toxicity of the specific elements involved; soil physical and chemical properties; occurrence and bioavailability of HM ions in the soil solution; and soil rhizosphere chemistry. HMs can disrupt the normal structure and function of cellular components and impede various metabolic and developmental processes. This review evaluates: (1) HM contamination in arable lands through agricultural practices, particularly due to chemical fertilizers, pesticides, livestock manures and compost, sewage-sludge-based biosolids, and irrigation; (2) factors affecting the bioavailability of HM elements in the soil solution, and their absorption, translocation, and bioaccumulation in crop plants; (3) mechanisms by which HM elements directly interfere with the physiological, biochemical, and molecular processes in plants, with particular emphasis on the generation of oxidative stress, the inhibition of photosynthetic phosphorylation, enzyme/protein inactivation, genetic modifications, and hormonal deregulation, and indirectly through the inhibition of soil microbial growth, proliferation, and diversity; and (4) visual symptoms of highly toxic non-essential HM elements in plants, with an emphasis on crop plants. Finally, suggestions and recommendations are made to minimize crop losses from suspected HM contamination in agricultural soils.Arts and Social Sciences, Irving K. Barber Faculty of (Okanagan)Non UBCBiology, Department of (Okanagan)ReviewedFacult