David R. Clements

Promotion of weed species diversity and reduction of weed seedbanks with conservation tillage and crop rotation

Abstract In a 6-yr study on four farms (36 fields) in Ontario, Canada, we tested the effects of tillage (moldboard, chisel plow, no tillage) and crop rotations (continuous corn, corn-soybean, corn-soybean-winter wheat) on emerged and seedbank weed species diversity and density. Aside from the imposed experimental treatments, all other management was generally consistent among farms. Tillage had the largest effect on weed diversity and density. No tillage promoted the highest weed species diversity, chisel plow was intermediate, and moldboard plow resulted in the lowest species diversity. These results are consistent with ecological succession theory. The increase in weed species diversity resulted from 20 species being associated with no tillage systems, 15 of which were winter annuals, biennials, or perennials. Emerged weed density was affected only by tillage. Over 6 yr, seedbank declined in no-tillage systems from 41,000 to 8,000 seeds m−3. Crop yields were not affected by tillage or crop rotation. In practical terms, reduced tillage in combination with a good crop rotation may reduce weed density and expenditures on weed management. Nomenclature: Glyphosate; corn, Zea mays L. ‘Pioneer 3902’; soybean, Glycine max (L.) Merr. ‘KG 40’; winter wheat Triticum aestivum L.

Recent improvements in the energy efficiency of agriculture: Case studies from Ontario, Canada

Abstract Energy used (GJ) per tonne of crop produced defines energy efficiency. Low energy use/tonne of crop produced indicates higher energy efficiency. Because of improved crop breeding (more stress tolerance, genetic gain) crop yields have increased. Concurrently, energy used has decreased. Based on an analysis of energy use/crop produced for Ontarios major row crops (corn and soybean), energy efficiency of crop production increased from 1975 to 1991. In corn, energy efficiency increased 49.8% from 87.95 l of diesel fuel equivalent (LDFE)/t of crop produced to 44.16 LDFE/t from 1975 to 1991. Total corn production (t) and yield (t/ha) increased by 60.0% and 20.1%, respectively, whereas energy use/ha (LDFE/ha) and total energy use (LDFE) decreased by 39.7% and 19.7%, respectively. For soybean, energy use/ha (LDFE/ha) decreased by 46.3% but total energy use (LDFE) increased by 93.8%. The increase in total energy use was caused by a 260.8% increase in soybean acreage (ha). Because the increase in soybean production (t) of 278.2% was much greater than the increase in total energy use (LDFE), energy efficiency increased 48.7% from 75.46 LDFE/t to 38.67 LDFE/t. The proportion that fertilizer manufacturing contributes to total annual energy use in corn decreased slightly (74.2–71.0%) between 1975 and 1991; however, energy use in fertilizer manufacturing declined by 42.4% because of the increased efficiency of manufacturing nitrogen fertilizers. Increased efficiency of fertilizer application also decreased energy use, although application is a much smaller proportion of the total energy use budget. Similar decreases occurred in soybean production. Our analysis of no-till systems using various herbicides and application rates indicated that the systems using the highest herbicide application rates required the least energy, because decreased herbicide application rates may require increased cultivation. This, however, depends on the timing (pre-plant, planting, post-emergent) and type (banded, broadcast) of application and is true only for newer herbicides with low application rates.

The biology of Canadian weeds. 112. Ulex europaeus L.

Gorse (Ulex europaeus L.) is a leguminous shrub native to western Europe and North Africa. During the past century it has greatly expanded its adventive range in Australia, New Zealand, Chile and Europe, and along the Pacific and Atlantic coasts of North America. In Canada, it is found in British Columbia (Vancouver, Vancouver Island, the Gulf Islands and Queen Charlotte Islands) where it is classed as a noxious weed. Gorse is also found from Virginia to Massachusetts on the east coast of North America. The shrub rapidly invades dry and disturbed areas, forming dense thickets that can suppress and inhibit native vegetation, including economically important conifer seedlings. It can occupy the same habitats as Scotch broom [Cytisus scoparius (L.) Link] but usually occurs on drier sites. Both of these legumes threaten native plant communities but U. europaeus persists longer and possesses conspicuous spines. Invasive characteristics of gorse include its evergreen habit, prolific seed production, longevity o...

Evaluation of alternative weed management systems in a modified no-tillage corn–soybean–winter wheat rotation: weed densities, crop yield, and economics

Abstract A 9-yr (1990–1998) study was conducted at Woodstock, ON, Canada, to evaluate weed densities, crop yields, and gross returns in a modified no-tillage (no primary tillage) corn–soybean–winter wheat rotation under three weed management treatments: (1) minimum, preplant application of glyphosate followed by mechanical control; (2) integrated weed management (IWM), preplant application of glyphosate followed by band application of preemergence herbicides plus mechanical control; and (3) conventional, preplant application of glyphosate followed by broadcast application of preemergence herbicides in corn and soybean. In wheat the minimum and IWM treatments had no additional weed control measures other than the preplant application of glyphosate, whereas the conventional treatment had a broadcast application of a postemergence herbicide. Weed densities were assessed each year, (except in 1990) once during the growing season in corn and soybean and immediately after crop harvest in wheat. Adjusted gross return was calculated as the gross revenue minus the unique costs for weed control for each of the treatments. Weed densities were greater in the minimum treatment compared with the IWM or conventional treatment in all crops. Weed densities in the IWM and conventional treatments did not differ. There was no apparent “buildup” of weed density with time in the rotation resulting from weed escapes. Hence, these data challenge current thinking that weed densities increase with time if weed escapes are allowed to go to seed. Corn and soybean yields in the IWM and conventional treatments did not differ. However, the minimum treatment had the lowest corn and soybean yields. Winter wheat yield was not affected by the treatments. All weed management treatments provided similar gross returns for each crop and for the rotation. Thus, the minimum treatment consisting of glyphosate applied preplant followed by shallow interrow tillage appeared to be a viable option, especially if practiced in a farming system capable of ensuring adequate timing of cultivation operations. Nomenclature: Glyphosate; imazethapyr; linuron; metolachlor; MCPB and MCPA; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; winter wheat, Triticum aestivum L.

Management in a modified no-tillage corn–soybean–wheat rotation influences weed population and community dynamics

Abstract Conservation tillage systems, such as no-tillage, are ecologically advantageous because they reduce soil erosion; however, they rely heavily on herbicide use. Our goal was to determine how weed communities of no-tillage systems are affected when the system is modified to reduce herbicide use through a combination of banded herbicides and interrow cultivation. To this end, we conducted a 9-yr study in a no-tillage corn–soybean–winter wheat rotation. All management systems had a preplant application of glyphosate, followed by either broadcast PRE herbicides (conventional no-tillage), interrow cultivation with banded PRE herbicides, or interrow cultivation alone. Aboveground weed densities were assessed each year and data were grouped into early (1991 to 1993) and late (1996 to 1998) time periods. Over time, weed communities became more distinct, showing a strong response to management and crop. In the early years, weed communities separated more in response to management than crop. In the late years, this was reversed. Weed communities in systems with interrow cultivation were more diverse than those in conventional no-tillage. The response to weed management system and crop was species specific. For example, the abundance of yellow foxtail was higher when interrow cultivation was employed, but abundance was equal in all crops. Dandelion was more abundant in conventional no-tillage of corn and soybean; however, it was equally abundant in all management systems in wheat. Seed bank species richness increased over time and was highest in systems with interrow cultivation. Herbicide use can be reduced in a modified no-tillage corn–soybean–wheat rotation by incorporating interrow cultivation, with or without banded herbicides, into the management plan. The weed community trajectory changes, and the weed community becomes more diverse. A more diverse weed community will not necessarily alter how we manage weeds. Nomenclature: Glyphosate; yellow foxtail, Setaria glauca (L.) Beauv.; dandelion, Taraxacum officinale Weber; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.

The biology of invasive alien plants in Canada. 9. Impatiens glandulifera Royle.

Impatiens glandulifera Royle (Himalayan balsam) is an invasive alien annual up to 3 m in height with showy flowers that are generally pink or purplish. Native to the Himalayan region, I. glandulifera was first recorded in Canada in 1901 in Ottawa, and is now found in eight Canadian provinces: British Columbia, Manitoba, Ontario, Quebec, Nova Scotia, New Brunswick, Prince Edward Island and Newfoundland. Impatiens glandulifera is typically found in riparian habitats and may spread rapidly because its seeds are readily transported via waterways. Up to 2500 seeds are produced per plant and dispersed explosively up to 5 m from the parent plant. This can result in dense monotypic stands which prevent establishment of native plants and make stream banks vulnerable to erosion when the shallow-rooted plants die back. Impatiens glandulifera is susceptible to glyphosate but because herbicide use in riparian areas is not advised, other control methods such as hand weeding, mowing or flaming have been used. Methods fo...

The biology of Canadian weeds. 116. Echium vulgare L.

Echium vulgare L., known as blueweed or viper’s bugloss, is a blue or purple flowered biennial or short-lived monocarpic perennial herb found in every province in Canada. A naturalized weed of European origin, E . vulgare grows in highly disturbed are as, typically in soils of limestone or dolomite parent material. It is not competitive with crops, but serves as an alternate host for fungal pathogens and contains hepatotoxic alkaloids detrimental to livestock when consumed in large amounts. E. vulgare is a noxious weed in Nova Scotia, Quebec, Manitoba, Alberta and parts of British Columbia. Beneficial aspects include contributions to honey production and herbal medicine. Key words: Echium vulgare, blueweed, vipers bugloss, weed biology

New dimensions in agroecology

* Preface * New Dimensions in Agroecology for Developing a Biological Approach to Crop Production (David R. Clements and Anil Shrestha) * Education in Agroecology and Integrated Systems (Charles A. Francis) * Redesigning Industrial Agroecosystems: Incorporating More Ecological Processes and Reducing Pollution (Eugene P. Odum and Gary W. Barrett) * Integrating Agroecological Processes into Cropping Systems Research (Stephen R. Gliessman) * An Agroecological Basis for Designing Diversified Cropping Systems in the Tropics (Miguel A. Altieri and Clara I. Nicholls) * Soil Ecosystem Changes During the Transition to No-Till Cropping (Tami L. Stubbs, Ann C. Kennedy, and William F. Schillinger) * The Ecology of Crop-Weed Interactions: Towards a More Complete Model of Weed Communities in Agroecosystems (Bruce D. Maxwell and Edward Luschei) * Research and Extension Supporting Ecologically Based IPM Systems (Fabian D. Menalled, Douglas A. Landis, and Larry E. Dyer) * Effects of Key Soil Organisms on Nutrient Dynamics in Temperate Agroecosystems (Joann K. Whalen and Chantal Hamel) * Nutrient Dynamics: Utilizing Biotic-Abiotic Interactions for Improved Management of Agricultural Soils (Chantal Hamel, Christine Landry, Abdirashid Elmi, Aiguo Liu, and Timothy Spedding) * Microbial and Genetic Diversity in Soil Environments (Ping Wang and Warren A. Dick) * Impact of Global Change on Biological Processes in Soil: Implications for Agroecosystem Management (Shuijin Hu and Weijian Zhang) * The Importance of Biodiversity in Agroecosystems (Lori Ann Thrupp) * Biophysical and Ecological Interactions in a Temperate Tree-Based Intercropping System (N. V. Thevathasan, A. M. Gordon, J. A. Simpson, P. E. Reynolds, G. Price, and P. Zhang) * Agricultural Landscapes: Field Margin Habitats and Their Interaction with Crop Production (E. J. P. Marshall) * Benefits of Re-Integrating Livestock and Forages in Crop Production Systems (E. Ann Clark) * Nitrogen Efficiency in Mixed Farming Systems (Egbert A. Lantinga, Gerard J. M. Oomen, and Johannes B. Schiere) * Ecological Context for Examining the Effects of Transgenic Crops in Production Systems (Jennifer A. White, Jason P. Harmon, and D. A. Andow) * Redesigning Pest Management: A Social Ecology Approach (Stuart B. Hill) * Research Priorities in Natural Systems Agriculture (T. S. Cox, C. Picone, and W. Jackson) * Index * Reference Notes Included

The biology of Canadian weeds. 110. Tragopogon dubius Scop., Tragopogon pratensis L., and Tragopogon porrifolius L.

Several types of salsify or goats-beard, Tragopogon species (Asteraceae), are found in Canada as biennial or monocarpic perennial herbs with yellow or purple flowers. Introduced from Eurasia, T. pratensis and T. dubius have become established in all provinces in Canada except Newfoundland and the territories. Tragopogon porrifolius tends to be more local, but is also found in southern areas of most provinces. Tragopogon species hybridize readily, and the tetraploid species T. mirus and T. miscellus have resulted from crosses among the three diploid Tragopogon species in North America. Salsify species produce relatively large umbrella-like pappuses which promote long-distance dispersal. These species also invade rangeland, and are considered noxious weeds in some parts of Canada. Key words: Tragopogon dubius, Tragopogon pratensis, Tragopogon porrifolius, Tragopogon mirus, Tragopogon miscellus, salsify, goats-beard, Asteraceae, Compositae, hybridization, weed biology

Management Strategies for Invasive Plants in Pacific Northwest Prairies, Savannas, and Oak Woodlands

Abstract Invasion by non-native plant species is one of the greatest threats to prairie, savanna, and oak woodland habitats of the Willamette Valley-Puget Trough-Georgia Basin (WPG) ecoregion. Invasive plants can modify the diversity, structure, and function of natural habitats. Effects from non-native invasions have contributed to the decline of many native species found on Pacific Northwest prairie and oak habitats. Even with aggressive management, these unique habitats are severely impacted by nonnative plant invasions. Without management, native species diversity will continue to decline rapidly. Here we provide a list of invasive plants that have extensive detrimental impacts on prairies, savannas, and oak woodlands throughout the ecoregion as a resource for land managers. We provide technical descriptions for the most highly invasive shrubs, grasses, and forbs, current best management practices, and an outlook for the future. When available, we document results from experimental trials. Much of the information presented is based on field observations from experienced land managers. Invasive plants will continue to be a management priority in the WPG for the foreseeable future. Working cooperatively from an ecoregional perspective to track occurrence, develop and implement effective management, and monitor progress is the best platform for successful restoration of the prairies, savannas, and oak woodlands in the WPG ecoregion.