Drew J. Lyon

Changes in soil microbial community structure with tillage under long-term wheat-fallow management

Fatty acid methyl esters (FAMEs) were used to ‘fingerprint’ soil microbial communities that evolved during 25 years of wheat-fallow cropping following native mixed prairie sod at Sidney, Nebraska, USA. Total ester-linked FAMEs (EL-FAMEs) and phospholipid-linked FAMEs (PL-FAMEs) were compared for their ability to discriminate between plots remaining in sod and those cropped to wheat or left fallow under no-till, sub-till or plow management. Cropped plots were higher in microbial biomass than their fallowed counterparts, and did not diAer significantly with tillage for the 0‐15 cm depth. Under fallow, microbial biomass was greatest in no-till and least in plow. Both cluster and discriminant analysis of PL- and EL-FAMEs clearly separated the remaining native sod plots from the existing wheat-fallow plots. This separation was particularly pronounced for the EL-FAMEs and was largely driven by high amounts in sod of a single FAME, C16:1(cis11), which has been cited as a biomarker for arbuscular mycorrhizal (AM) fungi. Within wheat-fallow, C16:1(cis11) declined significantly from no-till to plow, which supports the origin of C16:1(cis11) from extraradical mycelium and spores of AM fungi known to be sensitive to soil disturbance. Although discriminant analysis of PL- and EL-FAMEs diAerentiated wheat and fallow systems by tillage, discrimination among tillage treatments was expressed most strongly during fallow. FAME profiles from fallow plow were most dissimilar from cropped soils which suggests a relationship between tillage management and the long-term resiliency of the microbial community developed under the wheat crop. 7 2000 Elsevier Science Ltd. All rights reserved.

Simulation Supplements Field Studies to Determine No-Till Dryland Corn Population Recommendations for Semiarid Western Nebraska

tem of wheat–summer crop–fallow increased the efficient use of precipitation by reducing the frequency of In a 2-yr multiple-site field study conducted in western Nebraska summer fallow and using more water for crop transpiraduring 1999 and 2000, optimum dryland corn (Zea mays L.) population varied from less than 1.7 to more than 5.6 plants m 2, depending tion (Farahani et al., 1998). In addition to increased largely on available water resources. The objective of this study was precipitation use efficiency and grain yield, more intento use a modeling approach to investigate corn population recommensified dryland cropping systems increase potentially acdations for a wide range of seasonal variation. A corn growth simulative surface soil organic C and N (Peterson et al., 1998), tion model (APSIM-maize) was coupled to long-term sequences of effectively control winter annual grass weeds in winter historical climatic data from western Nebraska to provide probabilistic wheat (Daugovish et al., 1999), and increase net return estimates of dryland yield for a range of corn populations. Simulated and reduce financial risk (Dhuyvetter et al., 1996). populations ranged from 2 to 5 plants m 2. Simulations began with Growers in the semiarid regions of western Nebraska one of three levels of available soil water at planting, either 80, 160, have had limited experience with dryland corn. Before or 240 mm in the surface 1.5 m of a loam soil. Gross margins were 1997, fewer than 3800 ha of dryland corn were planted maximized at 3 plants m 2 when starting available water was 160 or 240 mm, and the expected probability of a financial loss at this populaeach year in the western crop-reporting district. As more tion was reduced from about 10% at 160 mm to 0% at 240 mm. When growers diversified and intensified their rotations, land starting available water was 80 mm, average gross margins were less planted to corn grew to more than 28 700 ha in 1999 than

Secale cereale interference and economic thresholds in winter Triticum aestivum

15 ha 1, and risk of financial loss exceeded 40%. Median yields (NASS, 2000). Growers were getting conflicting populawere greatest when starting available soil water was 240 mm. However, tion recommendations and requested assistance from perhaps the greater benefit of additional soil water at planting was the University of Nebraska. reduction in the risk of making a financial loss. Dryland corn growers Determining population response of corn is a recurin western Nebraska are advised to use a population of 3 plants m 2 rent area of study, with modern hybrids having greater as a base recommendation. tolerance of high plant density than older hybrids (Tollenaar, 1991). In one southwest Kansas study, dryland corn performed best when no-till–planted in early to W is the most limiting resource for dryland mid-May at plant populations not exceeding 4.45 plants crop growth in the semiarid areas of the U.S. m 2 (Norwood and Currie, 1996). A more recent study Great Plains (Smika, 1970). Summer fallow, the practice from this same region achieved maximum yield and of controlling all plant growth during the noncrop seawater use efficiency with a late May planting, combined son, is commonly used to stabilize winter wheat (Tritiwith later-maturing hybrids and plant populations up to cum aestivum L.) production in this region of high envi6.0 plants m 2 (Norwood, 2001). However, in northwest ronmental variability. Wheat–fallow is the predominate Kansas, no yield differences were found for corn populacropping system in the Great Plains, but water storage tions of 2.1, 2.47, and 3.71 plants m 2 (Havlin and Lamm, efficiency during fallow is frequently less than 25% with 1988). In a summary of research results from locations conventional tillage (McGee et al., 1997). The advent across the USA and Canada, corn grain yields leveled of reducedand no-till systems has generally enhanced off but did not decrease above the optimum plant poputhe ability to capture and retain precipitation in the soil lation, except in those fields with yield levels below 7500 during noncrop periods of the cropping cycle, making kg ha 1 (Paszkiewicz and Butzen, 2001). it more feasible to reduce the frequency of fallow and Blumenthal et al. (2003) advised dryland corn growers intensify cropping systems relative to wheat–fallow (Peto use a plant population of 2.7 plants m 2, based on terson et al., 1996). 2 yr of field research conducted at four locations each In the Great Plains, annual precipitation is concenyear. Unfortunately, summer precipitation was very diftrated during the warm season from April to September. ferent between the 2 yr of the study, and often the Hence, inclusion of a summer crop, e.g., corn or grain treatment resulting in the greatest yield in 1 yr provided sorghum [Sorghum bicolor (L.) Moench], in a 3-yr systhe least yield in the other year. The standard analysisof-variance approach used in that study did not allow D.J. Lyon and J.M. Blumenthal, Panhandle Res. and Ext. Cent, 4502 for a satisfactory assessment of the production risks Ave. I, Scottsbluff, NE 69361; and G.L. Hammer and G.B. McLean, Agric. Prod. Syst. Res. Unit, QDPI, PO Box 102, Toowoomba, QLD, associated with the various population treatments. Australia 4350. Journal Ser. no. 13756 of the Univ. of Nebraska Agric. Crop modeling has been a developing component of Res. Div. Received 11 July 2002. *Corresponding author (DLYON1@ agronomic research for more than 30 yr (Sinclair and unl.edu). Seligman, 1996). Crop models have been successfully used to analyze management practice in regions where Published in Agron. J. 95:884–891 (2003).

13C discrimination in corn grain can be used to separate and quantify yield losses due to water and nitrogen stresses

Abstract Secale cereale is a serious weed problem in winter Triticum aestivum–producing regions. The interference relationships and economic thresholds of S. cereale in winter T. aestivum in Colorado, Kansas, Nebraska, and Wyoming were determined over 4 yr. Winter T. aestivum density was held constant at recommended planting densities for each site. Target S. cereale densities were 0, 5, 10, 25, 50, or 100 plants m−2. Secale cereale–winter T. aestivum interference relationships across locations and years were determined using a negative hyperbolic yield loss function. Two parameters—I, which represents the percent yield loss as S. cereale density approaches zero, and A, the maximum percent yield loss as S. cereale density increases—were estimated for each data set using nonlinear regression. Parameter I was more stable among years within locations than among locations within years, whereas maximum percentage yield loss was more stable across locations and years. Environmental conditions appeared to have a role in the stability of these relationships. Parameter estimates for I and A were incorporated into a second model to determine economic thresholds. On average, threshold values were between 4 and 5 S. cereale plants m−2; however, the large variation in these threshold values signifies considerable risk in making economic weed management decisions based upon these values. Nomenclature: Secale cereale L. SECCE, rye; Triticum aestivum L., wheat.

Winter Wheat Response to Preplant Applications of Aminocyclopyrachlor

Abstract It is difficult to quantify the mechanism(s) responsible for competition-induced yield loss using traditional experimental techniques. A technique using yield and 13C discrimination (Δ) for wheat, a C3 plant, has been developed to separate total yield loss (TYL) into yield loss due to N (YLNS) and water (YLWS) stresses. The objective of this research was to determine whether the Δ approach could be used in corn, a C4 plant, to separate TYL into YLNS and yield loss due to a combination of water and light stresses (YLWLS). The field study had a factorial design using five corn densities and five N rates and was conducted in western Nebraska in 1999 and 2000. Relationships for YLNS and YLWLS with TYL were derived from only a portion of the yield and Δ data collected in 1999 and validated based on the remaining data collected in 1999 and 2000. In 1999, 20 to 40% of TYL was due to YLWLS, whereas in 2000, a dry year, YLWLS accounted for 60 to 80% of the TYL. Results from using the Δ-based approach were consistent with analysis of variance results. For example, calculated YLWLS values were related to measured YLWLS by the equation: calculated YLWLS = 19 + 0.91 (measured YLWLS) (r2 = 0.95; P < 0.01). The Δ approach, based on a plants physiological response to the environment, can be used to separate and quantify competition-induced YLNS and YLWLS in corn. Nomenclature: Corn, Zea mays L.; wheat, Triticum aestivum L.

Imazamox for Winter Annual Grass Control in Imidazolinone-Tolerant Winter Wheat

Abstract Field studies were conducted in Wyoming and Nebraska in 2007 through 2009 to evaluate winter wheat response to aminocyclopyrachlor. Aminocyclopyrachlor was applied at rates between 15 and 120 g ai ha−1 6, 4, and 2 mo before winter wheat planting (MBP). Redroot pigweed control was 90% with aminocyclopyrachlor rates of 111 and 50 g ha−1 when applied 4 or 2 MBP. Aminocyclopyrachlor at 37 g ha−1 controlled Russian thistle 90% when applied 6 MBP. At Sidney, NE, winter wheat yield loss was > 10% at all aminocyclopyrachlor rates when applied 2 or 4 MBP, and at all rates > 15 g ha−1 when applied 6 MBP. At Lingle, WY, > 40% winter wheat yield loss was observed at all rates when averaged over application timings. Although the maturing wheat plants looked normal, few seed were produced in the aminocyclopyrachlor treatments, and therefore preharvest wheat injury ratings of only 5% corresponded to yield losses ranging from 23 to 90%, depending on location. The high potential for winter wheat crop injury will almost certainly preclude the use of aminocyclopyrachlor in the fallow period immediately preceding winter wheat. Nomenclature: Aminocyclopyrachlor; redroot pigweed, Amaranthus retroflexus L., AMARE; Russian thistle, Salsola tragus L. SASKR; winter wheat, Triticum aestivum L

Pest Management Implications of Glyphosate-Resistant Wheat (Triticum aestivum)in the Western United States1

Field experiments were conducted at five locations in Kansas, Nebraska, and Wyoming to determine the effects of imazamox rate and application timing on winter annual grass control and crop response in imidazolinone-tolerant winter wheat. Imazamox at 35, 44, or 53 g ai/ha applied early-fall postemergence (EFP), late-fall postemergence, early-spring postemergence (ESP), or late-spring postemergence (LSP) controlled jointed goatgrass at least 95% in all experiments. Feral rye control with imazamox was 95 to 99%, regardless of rate or application timing at Hays, KS, in 2001. Feral rye control at Sidney, NE, and Torrington, WY, was highest (78 to 85%) with imazamox at 44 or 53 g/ha. At Sidney and Torrington, feral rye control was greatest when imazamox was applied EFP. Imazamox stunted wheat <10% in two experiments at Torrington, but EFP or LSP herbicide treatments in the Sidney experiment and ESP or LSP treatments in two Hays experiments caused moderate (12 to 34%) wheat injury. Wheat injury increased as imazamox rate increased. Wheat receiving imazamox LSP yielded less grain than wheat treated at other application timings in each Hays experiment and at Sidney in 2001. No yield differences occurred in one Torrington experiment. However, yields generally decreased as imazamox application timing was delayed in the other Torrington experiment. Generally, imazamox applied in the fall provided the greatest weed control, caused the least wheat injury, and maximized wheat yield. Nomenclature: Imazamox; feral rye, Secale cereale L. #3 SECCE; jointed goatgrass, Aegilops cylindrica Host # AEGCY; wheat, Triticum aestivum L. ‘CO980875’. Additional index words: Central Great Plains, herbicide-tolerant wheat, IMI-wheat. Abbreviations: EFP, early-fall postemergence; ESP, early-spring postemergence; KS-A, Hays, KS, experiment A; KS-B, Hays, KS, experiment B; LFP, late-fall postemergence; LSP, late-spring postemergence; MSO, methylated seed oil; NE, Sidney, NE; UAN, urea ammonium nitrate; WY-A, Torrington, WY, experiment A; WY-B, Torrington, WY, experiment B.

Carfentrazone Improves Broadleaf Weed Control in Proso and Foxtail Millets

Glyphosate-resistant crop species have increased in number over the past decade as growers eagerly adopt this simple and effective weed management technology. Glyphosate-resistant wheat cultivars are being developed and may soon be available to growers. The objective of this paper is to discuss the pest management implications of glyphosate-resistant wheat in the western United States, a region stretching from the Great Plains to the Pacific Ocean that produces more than 80% of the nations wheat crop. The benefits of glyphosate-resistant wheat include: (1) improved weed control, particularly of difficult-to-control weeds, such as winter annual grasses belonging to the Aegilops, Avena, Bromus, Lolium, Poa, Secale, and Setaria genera; (2) an ability to control weeds resistant to currently available wheat herbicides; (3) an extended application window for control of late-emerging weeds; and (4) improved crop safety. Although these benefits are not to be minimized, they need to be considered in the light of the concerns surrounding this new technology in wheat. These concerns are about (1) the lack of an equally effective and affordable herbicide to control glyphosate-resistant volunteer wheat, which may increase wheat diseases such as wheat streak mosaic and Rhizoctonia root rot; (2) the possibility that overreliance on glyphosate will lead to species shifts, with unknown consequences for weed management in wheat; and (3) the use of multiple glyphosate-resistant crops in rotation with glyphosate-resistant wheat, which could rapidly increase glyphosate-resistant weeds, thereby limiting the future utility of glyphosate. If, or when, glyphosate-resistant wheat becomes commercially available, it will require careful management to sustain its usefulness. We have proposed several areas of research that we feel are critical to help develop sound management guidelines for deployment and use of this new weed management technology in wheat. These include (1) developing effective “green bridge” management strategies, i.e., using cultural and chemical approaches to control plants that sustain insect vector populations between wheat crop periods; (2) predicting potential weed species shifts resulting from the use of glyphosate-resistant wheat; and (3) developing management systems that include herbicide-resistant wheat on a rotational basis and rotating the use of glyphosate with other weed management strategies in the fallow period to minimize the potential development of glyphosate-resistant weeds or weed communities. Nomenclature: Glyphosate; Rhizoctonia root rot, Rhizoctonia solani Kühn; wheat, Triticum aestivum L. Additional index words: Herbicide-resistant crops, wheat streak mosaic virus. Abbreviations: ACCase, acetyl-coenzyme A carboxylase (EC 6.4.1.2); ALS, acetolactate synthase (EC 4.1.3.18).

Feral Rye (Secale cereale) in Agricultural Production Systems

Proso and foxtail millets are regionally important dryland crops for the semiarid portions of the Central Great Plains. However, few herbicides are registered for use in either crop. The efficacy of carfentrazone was studied in proso millet from 2003 through 2005 at the University of Nebraska High Plains Agricultural Laboratory located near Sidney, NE, and in foxtail millet in 2004 and 2005 at the University of Wyoming Sustainable Agriculture Research and Extension Center near Lingle, WY. Carfentrazone was applied POST at 9.0, 13.5, and 18.0 g ai/ha with combinations of 2,4-D amine, prosulfuron, and dicamba. Although leaves of treated plants exhibited localized necrosis, leaves emerging after treatment were healthy. Grain and forage yields were not affected by the application of carfentrazone. Dicamba and 2,4-D amine provided visual control of 30% or less for buffalobur. Adding carfentrazone to one or both of these herbicides improved buffalobur control to 85% or greater. Carfentrazone applied at 18.0 g/ha improved Russian thistle, kochia, and volunteer sunflower control in 2003, when plants were drought-stressed, but did not help with these and other weeds during wetter years. Carfentrazone provides proso millet producers with a way to selectively control buffalobur, a noxious weed in several western states. In foxtail millet, carfentrazone provides POST broadleaf weed control with little risk for serious crop injury. Crop injury has been a concern with 2,4-D, which is currently the only other herbicide registered for use in foxtail millet. Nomenclature: Carfentrazone, 2,4-D, dicamba, prosulfuron, buffalobur, Solanum rostratum Dun. SOLCU, kochia, Kochia scoparia (L.) Schrad. KCHSC, Russian thistle, Salsola iberica Sennen & Pau SASKR, foxtail millet, Setaria italica (L.) P. Beauv, proso millet, Panicum miliaceum L, sunflower, Helianthus annuus L

Evaluation of models predicting winter wheat yield as a function of winter wheat and jointed goatgrass densities

Feral rye, commonly referred to as cereal, winter, common, or volunteer rye, is an important weed in winter wheat production in many parts of the United States and the world. Feral rye reduces net profits in the United States by more than