Chemical Fallow Research Articles

Pea and Barley Forage as Fallow Replacement for Dryland Wheat Production

Core Ideas Forage yields from pea, especially winter pea, were competitive with hay barley yields.Crude protein yield from pea forage was 40 to 110% greater than barley.Crop harvest at the bloom stage used the least soil water and nitrogen.Wheat yield following pea averaged 82 to 88% of that on chemical fallow. There is a growing interest in the use of annual forages in rotation with wheat (Triticum aestivum L.). The objectives of this study were to: (i) compare forage yield and quality of spring and winter pea (Pisum sativum L.), barley (Hordeum vulgare L.), and a pea–barley mixture harvested at flowering (early), pod (late), or grown to maturity; and (ii) compare the cropping‐sequence effects of these cropping treatments for three N fertilizer rates, subsequent wheat yield, and grain quality relative to chemical fallow. This study was conducted at Amsterdam, MT, from 2003 to 2006. Pea forage yield at the pod stage was 1.2 Mg ha−1 (30%) and 3.7 Mg ha−1 (60%) greater than at the flower stage for spring and winter pea, respectively. At the same harvest times, spring barley forage averaged 1.8 Mg ha−1 (32%) greater either as a sole species or when mixed with spring pea. Forage quality of pea forage was high regardless of harvest timing. Protein yield for spring and winter pea forage averaged 0.28 (60%) and 0.38 Mg ha−1 (81%) greater than the barley forage treatments across harvest times and years. Significant differences in stored soil water (19 mm) and soil nitrate N (10 kg N ha−1) were found between flowering and pod forage harvest timing in pea, but these differences only nominally affected subsequent wheat yield or quality. Wheat following pea averaged approximately 85% of the yield on chemical fallow. Among the cropping treatments, the greatest wheat yield and protein occurred following winter pea harvested at the flower stage.

Relay-cropping and Fallow Programs for Strawberry-based Production System: Effects on Crop Productivity and Weed Control

Many strawberry growers in Florida relay crop vegetables with strawberries or grow multiple crops on the same plastic mulch. The practice can reduce the overall input costs per crop but weed management can be problematic. Field experiments designed as a split plot were conducted in Balm and Dover, FL over two successive strawberry-growing seasons from Oct. 2014 to Mar. 2015 (year 1) and Oct. 2015 to Mar. 2016 (year 2) and two successive muskmelon-growing seasons from March to July 2015 (year 1) and March to July 2016 (year 2). The objectives were to examine the effect of summer fallow programs and the presence or absence of a relay-crop on weed density and strawberry (Fragaria ×ananassa Duchesne) and muskmelon (Cucumis melo L.) yields. Summer fallow programs included leaving the plastic mulch in place and reusing it in year 2, a sunn hemp (Crotalaria juncea L.) cover crop, or a conventional chemical fallow. Relay cropping muskmelon with strawberries had no effect on strawberry yield. Summer fallow programs had no effect on muskmelon growth and yield in Balm and Dover, as well as strawberry growth and yield in Balm. In Dover, the plastic mulch summer fallow had 22% to 34% lower berry yield in year 2 compared with cover crop and chemical fallow, respectively. In year 2, relay-cropping was more effective in reducing total weed density compared with strawberry monoculture in Dover but not in Balm. In year 2 in Dover, averaged overall summer fallow programs, the total weed density was ≈3-fold less in relay-cropping than strawberry monoculture. Of all the summer fallow programs evaluated, leaving the plastic mulch in place combined with glyphosate was the most effective summer fallow program, whereas the conventional chemical fallow was the least effective at weed suppression. We conclude that relay cropping or double use of plastic mulch for successive strawberry crops are viable options for Florida strawberry growers.

Producing High‐Residue, No‐Till Fallow in the Low‐Rainfall Zone of the Pacific Northwest

Core Ideas Use of a stripper header to leave tall stubble for high‐residue no‐till. Winter triticale outperforms winter wheat in low rainfall dryland production. Tall crop residue reduces wind speeds at the soil surface. The low‐rainfall wheat production zone of eastern Washington is subject to wind erosion because of fine‐textured soils, low soil organic matter content, and tillage‐based winter wheat–summer fallow practices. Annual no‐till spring cropping systems to replace the low‐residue, erosive summer‐fallow period have not been economical. We conducted a 4‐year study at Ralston, WA to evaluate winter triticale (× Triticosecale) and non‐semi‐dwarf winter wheat (Triticum aestivum) biomass production, yield, nutrient use efficiency, and seed‐zone soil moisture during no‐till fallow and establishment of fall‐seeded canola. Treatments included winter triticale and winter wheat, both harvested with either a stripper header or conventional cutter‐bar header. Winter triticale produced more grain per pound of N fertilizer and per inch of soil water available than winter wheat, and overall yield was 30–80% greater than that of winter wheat. Full‐height cereals produced 20–90% more biomass than semi‐dwarf winter wheat. Stripper‐header triticale stubble maintained with no‐till chemical fallow (NTCF) reduced average wind speed at the soil surface to less than one‐half of the average wind speed recorded over reduced‐tillage winter wheat fallow. Soil moisture in the 0‐ to 3‐inch seed zone was greater and more uniform in stripper‐header no‐till fallow than in reduced‐tillage fallow. Maintenance of soil moisture by stripper‐header standing stubble was conducive to timely planting and establishment of fall‐seeded canola and led to greater crop establishment in no‐till fallow. Growing a high‐biomass cereal crop such as winter triticale or standard‐height winter wheat and harvesting with a stripper header produces a high‐residue, no‐till fallow that is a viable alternative to the traditional winter wheat–fallow cropping system.

Grain Sorghum Response to Nitrogen Fertilizer following Cover Crops

Grain sorghum growth and development was affected by cover crop and N management. Sorghum–sudangrass cover crop prior to grain sorghum required N to maintain yield. Late maturing soybean cover crop increased grain sorghum yield at suboptimal N rates. Late maturing soybean cover crop, N fertilizer replacement value of 44 kg N ha–1. Cover crops (CCs) can affect N fertilizer management by influencing nutrient cycling and N fertilizer requirement. Cropping systems with different CCs were established in 2007 to examine the response of sorghum [Sorghum bicolor (L.) Moench]. Four CC treatments {summer legume, late‐maturing soybean [LMS; Glycine max (L.) Merr]; summer non‐legume, sorghum–sudangrass (SS; Sorghum bicolor × Sorghum bicolor var. sudanese); winter legume, crimson clover (CL; Trifolium incarnatum L.), and winter non‐legume, daikon radish (DR; Raphanus sativus L.)} as well as double‐crop soybean (DSB) and chemical‐fallow (CF) treatments were imposed after wheat (Triticum aestivum L.) harvest in a wheat–sorghum–soybean cropping system. Five N rates (0, 45, 90, 135, and 180 kg N ha–1) were applied to sorghum within 2 wk of planting. Aboveground sorghum biomass was collected after physiological maturity to determine total N uptake and grain yield. The cropping system managed with LMS increased grain yield (>9%), compared to other CCs and CF with zero N application. Cropping systems including CL, DR, and DSB had similar effects on grain yield relative to CF when N fertilizer was applied. Increasing N rates significantly increased grain yield and N uptake of grain sorghum following SS, indicating that soil N was limited in this cropping system. The addition of LMS as a summer legume CC has the potential to contribute N and replace CF, thus improving management of N resources.

Herbicide resistance in cereal production systems of the US Great Plains: A review

The US Great Plains comprise the major cereal producing states in the country. In the US, wheat (winter and spring wheat) was grown in 45 million acres in 2014, with a total production of 55 M metric tons. Wheat after chemical fallow (W-F) dominates > 90% of the dryland cropping systems of the Northern Great Plains of the US, where soil moisture (< 300 mm of average annual precipitation) is often the limiting factor for continuous cropping. In the Central Great Plains of the US, wheat-corn/grain sorghum-fallow (W-C/G-F) is a common dryland rotation. An over-reliance on herbicides for weed control in these no-till cropping systems has resulted in weed shifts and escalated cases of resistance evolution in weed populations to single or multiple site-of-action herbicides. Early detection, increased awareness of socio-economic implications of herbicide-resistant weeds, and adoption of diversified weed control tactics would mitigate the further evolution of multiple herbicide-resistant weed biotypes in cereal production systems.

Evaluating biodegradability of soil organic matter by its thermal stability and chemical composition

The stability of soil organic matter (SOM) as it relates to resistance to microbial degradation has important implications for nutrient cycling, emission of greenhouse gases, and C sequestration. Hence, there is interest in developing new ways to quantify and characterise the labile and stable forms of SOM. Our objective in this study was to evaluate SOM under widely contrasting management regimes to determine whether the variation in chemical composition and resistance to pyrolysis observed for various constituent C fractions could be related to their resistance to decomposition. Samples from the same soil under permanent pasture, an arable cropping rotation, and chemical fallow were physically fractionated (sand: 2000-50 μm; silt: 50-5 μm, and clay: <5 μm). Biodegradability of the SOM in size fractions and whole soils was assessed in a laboratory mineralization study. Thermal stability was determined by analytical pyrolysis using a Rock-Eval pyrolyser, and chemical composition was characterized by X-ray absorption near-edge structure (XANES) spectroscopy at the C and N K-edges. Relative to the pasture soil, SOM in the arable and fallow soils declined by 30% and 40%, respectively. The mineralization bioassay showed that SOM in whole soil and soil fractions under fallow was less susceptible to biodegradation than that in other management practices. The SOM in the sand fraction was significantly more biodegradable than that in the silt or clay fractions. Analysis by XANES showed a proportional increase in carboxylates and a reduction in amides (protein) and aromatics in the fallow whole soil compared to the pasture and arable soils. Moreover, protein depletion was greatest in the sand fraction of the fallow soil. Sand fractions in fallow and arable soils were, however, relatively enriched in plant-derived phenols, aromatics, and carboxylates compared to the sand fraction of pasture soils. Analytical pyrolysis showed distinct differences in the thermal stability of SOM among the whole soil and their size fractions; it also showed that the loss of SOM generally involved preferential degradation of H-rich compounds. The temperature at which half of the C was pyrolyzed was strongly correlated with mineralizable C, providing good evidence for a link between the biological and thermal stability of SOM.

No‐Tillage Cropping Systems Can Replace Traditional Summer Fallow in North‐Central Oregon

Winter wheat (Triticum aestivum L.)–summer fallow (WW–SF) using conventional tillage (CT), the predominant cropping system in eastern Oregon, has increased soil erosion and depleted soil organic carbon (SOC). This research evaluates no‐tillage (NT) systems designed to reduce these negative impacts on soil. In this long‐term experiment (2004–2010), WW–SF using CT was compared with annual winter wheat (WW–WW), annual spring wheat (SW–SW), annual spring barley (Hordeum vulgare L.) (SB–SB), winter wheat–chemical fallow (WW–CF), winter wheat–winter pea (Pisum sativum L.) (WW–WP), and winter wheat–spring barley–chemical fallow rotation (WW–SB–CF), using NT. Measurements included, phenology, plant population, grain yield and yield components, residues, SOC, soil moisture, and precipitation. Water‐use efficiency (WUE) was derived from precipitation and yield data. Under annual cropping, WW–WP and SB–SB produced higher yields than WW–WW and SW–SW. Grain yields in rotations with fallow (WW–SF, WW–CF, and WW–SB–CF) were not significantly different. On an annual basis, SB–SB and WW‐WP produced the highest and lowest yields, respectively. The WUEs of fallow rotations, SB–SB, and SW–SW, were not different but were higher than WUEs of WW–WP and WW–WW. Residue cover and SOC were highest under annual cropping systems and lowest following peas in WW–WP and SF in WW–SF. We conclude that rotations with fallow using NT (WW–CF and WW–SB–CF) can replace the traditional WW–SF system without yield penalty.

Soil ecotoxicity assessment of glyphosate use under field conditions: microbial activity and community structure of Eubacteria and ammonia-oxidising bacteria.

A plot-scale experiment was conducted to assess the impact of field application rates of glyphosate on soil microbial communities by taking measurements of microbial activity (in terms of substrate-induced respiration and enzyme activity) in parallel with culture-independent approaches to assessing both bacterial abundance and diversity. Two rates of glyphosate, alone or in a mixture with 2,4-dichlorophenoxyacetic acid, were applied directly onto the soil surface, simulating normal use in chemical fallow in no-till systems. No consistent rate-dependent responses were observed in the microbial activity parameters investigated in the field plots that were exposed to glyphosate. Denaturant gradient gel electrophoresis (DGGE) of the overall bacterial community (Eubacteria) and ammonia-oxidising bacteria (AOB) revealed no effects of the high rate of glyphosate on the structure of the communities in comparison with the control. No treatment effects were observed on the abundance of Eubacteria shortly after treatment in 2010, while a small but significant difference between the high rate and the control was detected in the first sampling in 2011. The abundance of AOB was relatively low during the study, and treatment effects were undetectable. The absence of negative effects on soil microbial communities in this study suggests that glyphosate use at recommended rates poses low risk to the microbiota.

Emergence and seed production of woolly cupgrass (Eriochloa villosa) in legume forage crops

Simard, M.-J., Nurse, R. E. and Darbyshire, S. J. 2015. Emergence and seed production of woolly cupgrass (Eriochloa villosa) in legume forage crops. Can. J. Plant Sci. 95: 539–548. Woolly cupgrass is an annual grass of East Asian origin now present in North America, particularly in the US corn belt. The species was found in Canada in 2000 (southern Quebec). New, mostly small, populations have been discovered every year since 2007 and the species became a nationally regulated and quarantined weed in 2011. In order to evaluate the potential use of perennial legumes to reduce established populations, the emergence pattern, density, biomass and seed production of a woolly cupgrass population were evaluated in plots either kept unmanaged (control), in chemical fallow (treated with sequential applications of glyphosate) or cropped with alfalfa or clover from 2009 to 2011. Every year, woolly cupgrass seedlings started to emerge early (Apr. 29 to May 05) and continued to emerge over a 26- to 85-d period. All unma...

Effective Preemergence and Postemergence Herbicide Programs for Kochia Control

Field experiments were conducted in 2011 through 2013 at the MSU Southern Agricultural Research Center near Huntley, MT, to evaluate the effectiveness of various PRE and POST herbicide programs for kochia control in the absence of a crop. PRE herbicides labeled for corn, grain sorghum, soybean, wheat/barley, and/or in chemical fallow were applied at recommended field-use rates. Acetochlor + atrazine,S-metolachlor + atrazine + mesotrione, and sulfentrazone applied PRE provided ≥91% control of kochia at 12 wk after treatment (WAT). Metribuzin, metribuzin + linuron, and pyroxasulfone + atrazine PRE provided 82% control at 12 WAT. PRE control with acetochlor + flumetsulam + clopyralid, pyroxasulfone alone, and saflufenacil + 2,4-D was ≤23% at 12 WAT. Paraquat + atrazine, paraquat + linuron, and paraquat + metribuzin controlled kochia ≥98% at 5 WAT. POST control with bromoxynil + fluroxypyr, paraquat, tembotrione + atrazine, and topramezone + atrazine treatments averaged 84% at 5 WAT, and did not differ from glyphosate. Control with POST-applied bromoxynil + pyrasulfotole, dicamba, diflufenzopyr + dicamba + 2,4-D, saflufenacil, saflufenacil + 2,4-D, saflufenacil + linuron was 67 to 78% at 5 WAT. Because of the presence of kochia resistant to acetolactate synthase-inhibiting herbicides at the test site, cloransulam-methyl was not a viable option for kochia control. In a separate greenhouse study, kochia accessions showed differential response to the POST herbicides (labeled for corn or soybean) tested. Tembotrione + atrazine, topramezone + atrazine, lactofen, or fomesafen effectively controlled the glyphosate-resistant kochia accession tested. Growers should utilize these effective PRE- or POST-applied herbicide premixes or tank mixtures (multiple modes of action) to control herbicide-resistant kochia accessions in the field. PRE herbicides with 8 wk of soil-residual activity on kochia would be acceptable if crop competition were present; however, a follow-up herbicide application may be needed to obtain season-long kochia control in the absence of crop competition.

Kochia Suppression with Cover Crops in Southwestern Kansas

Kochia (Kochia scoparia L.) is a well‐adapted weed found throughout the semiarid Great Plains and has increased in concern because biotypes with resistance to numerous herbicide modes of action are present, thus reducing options for control. The objectives of the research were to determine if cover crops growing during the fallow phase of a no‐till winter wheat (Triticum aestivum L.)–fallow cropping system could reduce kochia density and biomass without reducing subsequent winter wheat yields. Five fall‐sown cover crops of Austrian winter pea (Pisum sativum ssp. arvense), hairy vetch (Vicia villosa Roth.), winter triticale (Triticale hexaploide Lart.), and mixtures of Austrian winter pea‐winter triticale and hairy vetch‐winter triticale were evaluated and compared with chemical fallow and to five spring‐sown cover crops of spring lentil (Lens culinaris Medik.), spring pea (Pisum sativum L.), spring triticale, and mixtures of spring lentil‐spring triticale and spring pea‐spring triticale. Fall‐sown triticale alone or in mixture reduced kochia density by 78 to 94% and reduced kochia biomass by 98% compared with kochia in chemical fallow. Spring‐sown cover crops and kochia emerged together in early March; thus kochia density and biomass were not affected by these cover crops. Fall‐sown cover crops that produced more biomass were most effective at suppressing kochia density and biomass. All cover crops were terminated by either forage harvest or chemical application by June 1. Subsequent winter wheat yields varied by cover crop across years, and in general winter wheat after cover crops yielded comparable to or less than chemical fallow.

Crop-sequence effects on productivity in a wheat-based cropping system at Wongan Hills, Western Australia

Western Australian grain production is dominated by wheat, but growing wheat continually in unbroken sequences leads to increasing problems with soil nutrient depletion, root and leaf disease build-up, high weed burdens, and possibly other less well-defined production constraints. These can adversely affect both production and grain quality. Including breaks in the crop sequence in the form of break crops, pasture, or fallow can reduce these problems, but these breaks can be expensive to implement, in terms of both direct cost and forgone revenue. It is therefore critical to predict the response of subsequent wheat crops to a break in order to choose crop sequences rationally. We conducted a 4-year experiment at Wongan Hills, Western Australia, evaluating how wheat productivity in a wheat-based cropping sequence is affected by including wheat, barley, lupins, triazine-tolerant and Roundup Ready® canola, oaten hay, volunteer pasture, serradella pasture, and chemical fallow. Wheat yield responded positively to fallow, lupins, oaten hay, volunteer pastures and serradella but not to barley or canola when compared with continuous wheat. Responses depended on seasonal conditions; in a dry year, a very large response occurred after fallow but not after lupin or serradella, whereas in a wetter year, there were large responses after these crops. Fallowing, cutting hay, crop-topping lupins, and spray-topping volunteer and serradella pasture all reduced seedset of annual ryegrass dramatically, and reduced weed competition was a major contributor to the observed break crop responses. Nitrogen fixation by lupins and serradella and water storage by fallow in a dry year were also important, but soilborne diseases did not contribute to wheat yield responses. Some yield responses persisted for at least 3 years, and the contribution of effects of weed competition to yield responses increased over this time. These results emphasise the importance of understanding which productivity constraints are present in a cropping system at a given time when deciding whether a break is necessary and which is the most appropriate break. The results also emphasise the importance of managing the wheat crop after a break to maximise the response and its longevity.

Response of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) to alternative herbicides

Burton, N., Shirriff, S. W. and Beckie, H. J. 2014. Response of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) to alternative herbicides. Can. J. Plant Sci. 94: 1407–1411. A greenhouse study was conducted to examine the response of glyphosate-resistant (GR) plus acetolactate synthase (ALS) inhibitor-resistant kochia to five post-emergence herbicide treatments commonly used to control the weed species in chemical fallow, cereals, or oilseed crops in western Canada. The treatments, which were applied to two GR kochia biotypes and one non-GR (susceptible) biotype, included the labeled rate of dicamba, dicamba/fluroxypyr, dicamba/diflufenzopyr, MCPA/bromoxynil, and glufosinate. Both GR and non-GR biotypes responded similarly to each of the herbicide treatments. Although both GR biotypes were sensitive to the herbicides, MCPA/bromoxynil was the most effective treatment in reducing shoot biomass 3 wk after application (99%), followed by glufosinate (91%) then the dicamba mixtures (82%). Dicamba alone only suppressed kochia biomass (76% reduction).

Soil water conservation and nitrous oxide emissions from different crop sequences and fallow under Mediterranean conditions

Interest in fallowing as the drought adaptation strategy has increased recently due to the occurrence of frequent droughts in cropping areas of Australia. Weed management in a fallow is crucial as it affects the level of soil water and nitrogen conserved by this practice. Increased use of fallow has implications for nitrous oxide emissions as soil moisture is a major determinant of evolution of nitrous oxide. In a two year study, three types of fallow with different weed management were compared with wheat and canola crops in 2010 and the carry-over effects with wheat on all plots in 2011. The weeds in the fallows were managed either by herbicide (chemical fallow) or by tillage (cultivation fallow) and compared to an unweeded fallow (weedy fallow). The chemical fallow conserved most soil water followed by cultivation fallow, with the lowest soil water content in the weedy fallow. In addition, more weeds were observed in the wheat crop following weedy fallow. Low wheat and canola yields were measured in 2010 because of a drought, which also depleted soil water compared to the chemical and cultivation fallows. Therefore, fallow is a potential strategy for increasing crop yield under dry conditions. The results also indicated that weeds had a detrimental effect by reducing soil water content due to lack of timely weed management. To test the compatibility of fallow with climate-change mitigation, the nitrous oxide emissions were compared in the 2011 wheat crop. There was a temporal fluctuation in nitrous oxide emissions with increased rates of emission after top dressing with urea. Importantly, however, the nitrous oxide emission from wheat following fallow was not increased compared with wheat in the continuous cropping sequences. Therefore, this study found that fallowing with good weed control, could be used as a drought adaptation strategy without increasing nitrous oxide emissions in following crops.

Nitrogen Use in Durum and Selected Brassicaceae Oilseeds in Two‐Year Rotations

Brassicaceae oilseeds can serve as potential feedstocks for renewable biofuels to offset demand for petroleum‐based alternatives. However, little is known about oilseed crop yield potential and N use in semiarid, wheat (Triticum spp.)‐based cropping systems that dominate the northern Great Plains (NGP). A 5‐yr study was conducted in northeast Montana to investigate the yield potential of a direct seeded system of durum (T. durum Desf.) in rotation with either chemical fallow or three Brassicaceae oilseeds: camelina [Camelina sativa (L.) Crantz], crambe (Crambe abyssinica Hochst. ex R.E. Fries), and canola‐quality Brassica juncea L. Overall, results from the study indicated that seed yield in the three Brassicaceae oilseeds tested in rotation with durum was related (P &lt; 0.001; r2 = 0.68) to a nitrogen recovery index (NRI), indicating the importance of nitrogen use (NU) efficiency in dryland oilseed production, and that B. juncea generally used N more efficiently than crambe and camelina. Similarly, NRI was related (P &lt; 0.001; r2 = 0.72) to grain yield in durum following oilseeds. Grain yield of durum following B. juncea was similar to durum following fallow and greater than durum following camelina or crambe. Durum following crambe tended to use N more inefficiently than durum following camelina, B. juncea, or fallow. Differences in yield and N use of durum and oilseeds varied among years, which underscores the need to further develop management tools to optimize durum‐oilseed cropping systems in highly variable rainfall environments typical of the NGP.

Survey of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) in Alberta

Hall, L. M., Beckie, H. J., Low, R., Shirriff, S. W., Blackshaw, R. E., Kimmel, N. and Neeser, C. 2014. Survey of glyphosate-resistant kochia ( Kochia scoparia L. Schrad.) in Alberta. Can. J. Plant Sci. 94: 127-130. Glyphosate-resistant (GR) kochia was identified in Warner county in southern Alberta in 2011. To determine the scale of the distribution and frequency of GR kochia, a randomized stratified survey of more than 300 locations (one population per location) in southern Alberta was conducted in the fall of 2012. Mature plants were collected, seed separated, and F1 seedlings screened by spraying with glyphosate at 900 g a.e. ha-1 under greenhouse conditions. Screening confirmed 13 GR kochia sites: seven in Warner county, five in Vulcan county, and one in Taber county. The frequency of GR individuals in a population ranged from 0.3 to 98%. GR kochia were found in arid areas where chemical fallow is a significant component of the rotation. Economic and agronomic impact of this GR weed biotype is compou...

Survey of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) in Alberta

Hall, L. M., Beckie, H. J., Low, R., Shirriff, S. W., Blackshaw, R. E., Kimmel, N. and Neeser, C. 2014. Survey of glyphosate-resistant kochia ( Kochia scoparia L. Schrad.) in Alberta. Can. J. Plant Sci. 94: 127–130. Glyphosate-resistant (GR) kochia was identified in Warner county in southern Alberta in 2011. To determine the scale of the distribution and frequency of GR kochia, a randomized stratified survey of more than 300 locations (one population per location) in southern Alberta was conducted in the fall of 2012. Mature plants were collected, seed separated, and F1 seedlings screened by spraying with glyphosate at 900 g a.e. ha−1 under greenhouse conditions. Screening confirmed 13 GR kochia sites: seven in Warner county, five in Vulcan county, and one in Taber county. The frequency of GR individuals in a population ranged from 0.3 to 98%. GR kochia were found in arid areas where chemical fallow is a significant component of the rotation. Economic and agronomic impact of this GR weed biotype is compounded because of multiple resistance to acetolactate synthase-inhibiting herbicides.

Influence of Semiarid Cropping Systems on Root Diseases and Inoculum Density of Soilborne Pathogens

There is interest in converting the 2-year rotation of rainfed winter wheat with cultivated fallow in the Pacific Northwest of the United States into direct-seed (no-till) systems that include chemical fallow, spring cereals, and food-legume and brassica crops. Eight cropping systems in a low-precipitation region (<330 mm) were compared over 9 years to determine effects of changes on diseases. Fusarium crown rot was more prevalent in wheat following cultivated than chemical fallow, and Rhizoctonia root rot was more severe when winter wheat was rotated with chemical fallow than with no-till winter pea. Take-all occurred even during the driest years and was more severe on annual spring wheat than on annual spring barley. Inoculum density (picograms of DNA per gram of soil) differed (α < 0.05) among cropping systems for Fusarium culmorum, F. pseudograminearum, Gaeumannomyces graminis var. tritici, and Pythium spp. but not for Rhizoctonia solani AG-8. Phoma medicaginis var. pinodella was detected only where winter pea was planted frequently. This is the first report of P. medicaginis as a component of the dryland stem rot complex of pea in north-central Oregon. Results of this investigation will provide guidance for developing crop species with resistance to Fusarium crown rot and black stem of pea.

Effects of Crop Rotations and Tillage on Pratylenchus spp. in the Semiarid Pacific Northwest United States.

There is interest in converting rainfed cropping systems in the Pacific Northwest from a 2-year rotation of winter wheat and cultivated fallow to direct-seed (no-till) systems that include chemical fallow, spring cereals, and food legume and brassica crops. Little information is available regarding effects of these changes on plant-parasitic nematodes. Eight cropping systems in a low-precipitation region (<330 mm) were compared over 9 years. Each phase of each rotation occurred each year. The density of Pratylenchus spp. was greater in cultivated than chemical fallow, became greater with increasing frequency of host crops, and was inversely associated with precipitation (R2 = 0.92, α < 0.01). Densities after harvesting mustard, spring wheat, winter wheat, and winter pea were greater (α < 0.01) than after harvesting spring barley or spring pea. Camelina also produced low densities. Winter wheat led to a greater density of Pratylenchus neglectus and spring wheat led to a greater density of P. thornei. Density of Pratylenchus spp. was correlated (R2 = 0.88, α < 0.01) but generally higher when detected by real-time polymerase chain reaction on DNA extracts from soil than when detected by a traditional method. Selection of different Pratylenchus spp. by different wheat cultivars or growth habit must be addressed to minimize the level of nematode risk to future plantings of intolerant crops.

Wheat Cultivar Performance and Stability between No-Till and Conventional Tillage Systems in the Pacific Northwest of the United States

In Washington, over fifty percent of the wheat produced under rainfed conditions receives less than 300 mm of annual precipitation. Hence, a winter wheat-summer fallow cropping system has been established to obtain adequate moisture for winter wheat production. Current tilled fallow systems receive significant soil erosion through both wind and water. As a result, no-till chemical fallow systems are being adopted to mitigate erosion concerns. The objective of this study was to evaluate current Pacific Northwest cultivars under no-till chemical fallow and tilled fallow systems to identify cultivars adapted to a late-planted no-till system. Twenty-one cultivars were planted in a split-plot design with fallow type as the main plot and genotype as the sub-plot. Four replications were planted at two locations over three years. Data was collected on heading date, grain yield and grain volume weight. Analysis of variance was conducted on data from each year and location. Results were significant for all traits. Cultivars in the late-planted no-till system yielded an average of 39% less than the tilled fallow system. It is evident that cultivars vary in their adaptability and yield stability across production systems. Chukar and Eltan displayed the highest levels of yield stability, and growers who wish to plant winter wheat in a late-planted no-till system may benefit from choosing these cultivars.