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    Cropping systems alter plant volatile emissions in the field through soil legacy effects
    (Cambridge University Press, 2022-06) Malone, Shealyn C.; Menalled, Fabian D.; Weaver, David K.; Seipel, Tim F.; Hofland, Megan L.; Runyon, Justin B.; Bourgault, Maryse; Boss, Darrin L.; Trowbridge, Amy M.
    Crops emit a variety of volatile organic compounds (VOCs) that serve as attractants or repellents for pests and their natural enemies. Crop rotations, off-farm chemical inputs, and mechanical and cultural tactics – collectively called cropping systems – alter soil nutrients, moisture content, and microbial communities, all of which have the potential to alter crop VOC emissions. Soil legacy effects of diversified cropping systems have been shown to enhance crop VOC emissions in greenhouse studies, but how they influence emissions under field conditions remains virtually unknown. To determine the effect of cropping systems on plant VOC emissions in the field, air samples were collected from the headspace of wheat (Triticum aestivum L. Judee) grown in simplified wheat-fallow rotations or diversified wheat-cover crop rotations where cover crops were terminated by grazing cattle. Across two growing seasons, wheat grown in rotation with fallow emitted greater amounts of Z-3-hexenyl acetate and β-ocimene, key attractants for wheat stem sawfly (Cephus cinctus Norton), a major pest of wheat. While overall VOC blends were relatively similar among cropping system during the first growing season, emissions varied substantially in the second year of this study where wheat grown in rotation with cover crops emitted substantially greater quantities of volatile compounds characteristic of abiotic stress. Below-average precipitation in the second growing season, in addition to reduced soil water content in cover crop rotations, suggests that cropping system effects on wheat VOCs may have been driven primarily by water availability, a major factor limiting crop growth in dryland agriculture. While the specific mechanisms driving changes in VOC emissions were not explicitly tested, this work shows that agricultural practices applied in one growing season can differentially influence crop VOC emissions in the next through soil legacy effects, illustrating additional avenues through which cropping systems may be leveraged to enhance pest management.
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    Warm-Season Forage Options in Northern Dryland Regions
    (2020-06) Carr, Patrick M.; Boss, Darrin L.; Chen, Chengci; Dafoe, Julia M.; Eberly, Jed O.; Fordyce, Simon; Hydner, Roger M.; Fryer, Heather K.; Lachowiec, Jennifer A.; Lamb, Peggy F.; McVay, Kent A.; Khan, Qasim A.; Miller, Perry R.; Miller, Zachariah J.; Torrion, Jessica A.
    Rotating summer fallow with wheat (Triticum spp.) is done in dryland grain farming at upper latitudes to stabilize yields over time and to prevent crop failure. However, summer fallow is costly since weeds must be controlled and crops are not grown. Replacing summer fallow with grain crops can generate low economic returns. Previous research indicated that annual cool‐season forages can be substituted for summer fallow in dryland cropping systems. Our objective was to determine if annual warm‐season species were suited for forage production in monocultures and polycultures in the U.S. northern Great Plains. Dry matter (DM) production by 20 warm‐ and cool‐season crop monocultures and 4 polycultures was determined across six environments during 2016, and by 25 warm‐ and cool‐season crop monocultures and polycultures across four environments from 2016 through 2018. Maize (Zea mays L.) monoculture produced forage DM in amounts equal to, or greater than, those produced by other warm‐ and cool‐season crop treatments (P < 0.05). Maize DM production averaged 2.5 to 5.7 Mg ha−1, depending on the study and environment. Sorghum (Sorghum bicolor L.), foxtail millet [Setaria italica (L.) P. Beauv.] and sunflower (Helianthus annuus L.) also produced relatively large amounts of forage DM. Polycultures failed to produce more DM than monocultures consistently (P > 0.40). These results indicate that maize and other warm‐season crops are adapted for dryland forage production in cool regions at upper latitudes. Additional research is needed to determine the impacts of annual warm‐season forages on grain yield in a forage‐wheat crop sequence.
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