Kelly A. Nelson

Challenges and opportunities for mitigating nitrous oxide emissions from fertilized cropping systems

Nitrous oxide (N2O) is often the largest single component of the greenhouse-gas budget of individual cropping systems, as well as for the US agricultural sector as a whole. Here, we highlight the factors that make mitigating N2O emissions from fertilized agroecosystems such a difficult challenge, and discuss how these factors limit the effectiveness of existing practices and therefore require new technologies and fresh ideas. Modification of the rate, source, placement, and/or timing of nitrogen fertilizer application has in some cases been an effective way to reduce N2O emissions. However, the efficacy of existing approaches to reducing N2O emissions while maintaining crop yields across locations and growing seasons is uncertain because of the interaction of multiple factors that regulate several different N2O-producing processes in soil. Although these processes have been well studied, our understanding of key aspects and our ability to manage them to mitigate N2O emissions remain limited.

Differences in yields, residue composition and N mineralization dynamics of Bt and non-Bt maize

Cultivation of genetically modified crops may have several direct and indirect effects on soil ecosystem processes, such as soil nitrogen (N) transformations. Field studies were initiated in Northeast Missouri in 2002 and 2003 to determine grain and biomass yields and the effects of application of crop residues from five Bt maize hybrids and their respective non-Bt isolines on soil inorganic N under tilled and no-till conditions in a maize-soybean rotation. A separate aerobic incubation study examined soil N mineralization from residue components (leaves, stems, roots) of one Bt maize hybrid and its non-Bt isoline in soils of varying soil textural class. Three Bt maize hybrids produced 13–23% greater grain yields than the non-Bt isolines. Generally no differences in leaf and stem tissues composition and biomass was observed between Bt and non-Bt maize varieties. Additionally, no differences were observed in cumulative N mineralization from Bt and non-Bt maize residues, except for non-Bt maize roots that mineralized 2.7 times more N than Bt maize roots in silt loam soil. Incorporation of Bt residues in the field did not significantly affect soil inorganic N under tilled or no-till conditions. Overall Bt and non-Bt maize residues did not differ in their effect on N dynamics in laboratory and field studies.

Yellow Nutsedge (Cyperus esculentus) Control and Tuber Production with Glyphosate and ALS-Inhibiting Herbicides1

Greenhouse and field research evaluated yellow nutsedge growth, vegetative control, and tuber production after application of glyphosate, various acetolactase synthase (ALS)–inhibiting herbicides, and tank mixtures thereof. Yellow nutsedge was controlled by the herbicides halosulfuron at 35 g ai/ha, chlorimuron at 12 g ai/ha, and imazethapyr–imazapyr at 62 g ai/ha (> 70% control); imazethapyr at 70 g ai/ha, glyphosate at 840 g ae/ha, cloransulam at 17.5 g ai/ha, and rimsulfuron at 17.5 g ai/ha (40 to 70% control); and imazamox at 45 g ai/ha (< 40% control). Compared with the untreated control, tuber fresh weight in the field was reduced 45 to 91%, and tuber density was reduced 33 to 90% by all herbicide treatments 42 wk after treatment (WAT) except imazamox and rimsulfuron. Tuber sprouting was reduced to 19% in plots treated with halosulfuron and pyrithiobac compared with untreated yellow nutsedge 42 WAT. Chlorimuron and imazethapyr–imazapyr controlled yellow nutsedge at least 90%, prevented panicle formation, and reduced tuber density and fresh weight by 90% or more 14 WAT in the greenhouse. The addition of glyphosate to cloransulam or imazethapyr increased yellow nutsedge control and reduced tuber density and fresh weight when compared with either ALS-inhibiting herbicide or glyphosate applied alone. Tuber density data indicated that there were 8 tubers for every gram of tubers harvested. Yellow nutsedge height was 15 to 20 cm 4 to 5 wk after tillage, using growth analysis data. Long-term yellow nutsedge management may be aided with treatments that reduce tuber production. Nomenclature: Chlorimuron; cloransulam; glyphosate; halosulfuron; imazamox; imazapyr; imazethapyr; pyrithiobac; rimsulfuron; yellow nutsedge, Cyperus esculentus L. #3 CYPES. Additional index words: Acetolactase synthase inhibitor, plant height, postemergence, shoot production, tubers. Abbreviations: ALS, acetolactate synthase; COC, crop oil concentrate; DAS, diammonium sulfate ((NH4)2SO4); MSO, methylated seed oil; NIS, nonionic surfactant; WAT, weeks after treatment.

Effects of Protoporphyrinogen Oxidase Inhibitors on Soybean (Glycine max L.) Response, Sclerotinia sclerotiorum Disease Development, and Phytoalexin Production by Soybean1

Sclerotinia stem rot is an important soybean disease. An increase in phytoalexin production with herbicide treatments may reduce the incidence of this disease in soybean. Research was conducted to determine soybean response, Sclerotinia sclerotiorum lesion development, and phytoalexin production in glyphosate-resistant and -susceptible soybean cultivars treated with protoporphyrinogen oxidase–inhibiting herbicides. Necrosis of soybean leaves 7 d after postemergence application of oxyfluorfen at 17.5 g ai/ha, carfentrazone at 1.8 g ai/ha, sulfentrazone at 9.0 g ai/ha, fomesafen at 280 g ai/ha, acifluorfen at 425 g ai/ha, flumiclorac at 30 g ai/ha, CGA-248757 at 4 g ai/ha, and oxadiazon at 280 g ai/ha was equal to or less than lactofen at 70 g ai/ha. In a detached leaf bioassay, S. sclerotiorum lesion diameter was reduced by oxyfluorfen, carfentrazone, sulfentrazone, lactofen, fomesafen, flumiclorac, and oxadiazon compared with the untreated control. Furthermore, lesion diameter on untreated leaves of soybean treated with oxyfluorfen, carfentrazone, sulfentrazone, lactofen, fomesafen, acifluorfen, flumiclorac, CGA-248757, and oxadiazon was reduced compared with the untreated control. Lactofen and sulfentrazone increased leaf phytoalexin production similarly, but neither herbicide affected stem phytoalexin production compared with the untreated control. Glyphosate-resistant and near-isogenic–susceptible cultivars responded similarly when inoculated with S. sclerotiorum in the detached leaf bioassay. Glyphosate-resistant S20-B9 and P93B01 produced more phytoalexins than glyphosate-susceptible S 19-90 and P9281. Herbicide treatments may increase phytoalexin production in leaves of treated plants, but levels in the stem do not explain protection from Sclerotinia stem rot. Nomenclature: Acifluorfen; carfentrazone; CGA-248757, [[2-chloro-4-fluoro-5-[(tetrahydro-3-oxo-1H,3H-[1,3,4]thiadiazolo[3,4-a]pyridazin-1-yliden)amino]phenyl]thio]acetate (proposed common name, fluthiacet-methyl); flumiclorac; fomesafen; lactofen; oxadiazon; oxyfluorfen; sulfentrazone; soybean, Glycine max (L.) Merr. ‘Novartis S 19-90’ (‘S 19-90’), ‘Novartis S20-B9’ (‘S20-B9’), ‘Great Lakes 2415’ (‘GL2415’), ‘Great Lakes 2600’ (‘GL2600’), ‘Pioneer 9281’ (‘P9281’), ‘Pioneer 93B01’ (‘P93B01’); Sclerotinia stem rot, Sclerotinia sclerotiorum (Lib.) de Bary. Additional index words: Aryl triazinone, cultivar, cyclic imide, diphenyl ether, herbicide resistant, isolines, oxadiazole, phytotoxicity, postemergence, protoporphyrinogen inhibitor, Sclerotinia stem rot. Abbreviations: DAT, days after treatment; NIS, nonionic surfactant; GR, glyphosate resistant; protox, protoporphyrinogen oxidase; TLC, thin-layer chromatography; UAN, 28% urea ammonium nitrate.

Physiological basis for resistance to diphenyl ether herbicides in common waterhemp (Amaranthus rudis)

Abstract Common waterhemp seeds were collected from two Missouri soybean fields where biotypes were not controlled by acifluorfen. Plants grown from these seeds were tested for resistance to the diphenyl ether herbicides acifluorfen and lactofen. Resistance to susceptibility (R/S) ratios, calculated as the ratio of the dose required to inhibit dry weight accumulation by 50% (GR50) in resistant plants to that for susceptible plants, were 9.5 and 11 for the Meadville biotype and 28 and 44 for the Bethel biotype exposed to acifluorfen and lactofen, respectively. Electrolyte leakage assays determined that light-induced lipid peroxidation by acifluorfen was greatest on a control population (Bradford), intermediate for the Meadville biotype, and lowest for the Bethel biotype. Levels of the photodynamic pigment protoporphyrin IX (Proto) accumulating in leaf disks exposed to acifluorfen were much lower in the resistant biotypes than in the susceptible wild type, and the level of Proto accumulation was significantly correlated to the degree of membrane disruption. Although the binding of acifluorfen to protoporphyrinogen oxidase in chloroplasts may have been altered in the resistant biotypes, the molecular and biochemical factors involved in the mechanism of resistance remain to be fully characterized. However, this study establishes that the physiological basis for the evolved resistance to diphenyl ethers in common waterhemp rests on the reduction of Proto accumulation. Nomenclature: Acifluorfen; lactofen; common waterhemp, Amaranthus rudis Sauer AMATA; soybean, Glycine max (L.) Merr.

Glyphosate Application Timings in Twin- and Single-row Corn and Soybean Spacings

Field research was conducted in 2002 and 2003 to determine the effect of twin- and single-row spacing and POST glyphosate application timing on light interception, weed control, and grain yield of glyphosate-resistant corn and soybean. Row spacing did not affect light interception measured 10 to 11 wk after planting. Corn grain yield in 2002 was 1.0 Mg/ha higher in single rows compared with twin rows when averaged over glyphosate timing, but was unaffected by row spacing in 2003. Soybean grain yield was similar in 19- and 38-cm single rows, and single-row grain yield was 0.2 to 0.4 Mg/ha higher than the twin-row spacing. Corn grain yields were similar to the weed-free control when glyphosate was applied to weeds 10 to 15 cm tall in 2002 and 10 cm tall in 2003. Soybean yield was maximized by application of glyphosate to weeds 15 to 30 cm tall in 2002 and 60 cm tall in 2003. Nomenclature: glyphosate, corn, Zea mays L. ‘Wilcross 3149’, soybean, Glycine max (L.) Merr. ‘Asgrow 3701’

Zone herbicide application controls annual weeds and reduces residual herbicide use in corn

Abstract To minimize the chance of surface water contamination by herbicides, farmers need alternative ways to manage weeds in field crops, such as field corn, that reduce herbicide use. Zone herbicide application (ZHA) reduces herbicide use compared with conventional broadcast herbicide application by (1) banding low herbicide rates between corn rows (≤ 1× normal broadcast registered rate), (2) managing crops to favor crop competition, and (3) banding very low herbicide rates over crop rows (≪ 1× normal rate). The research goal was to compare the relative effectiveness of reduced-rate ZHA with broadcast herbicide application on in-row (IR) and between-row (BR) summer annual weed cover (chiefly giant foxtail and waterhemp species), grain yields, and net returns resulting from herbicide application in field corn. Preemergence ZHA of atrazine + metolachlor + clopyralid + flumesulam was made in zones (i.e., even width bands) at different rates between and over crop rows for three site-years in Missouri, and the 1× rate was 2.24 + 1.75 + 0.211 + 0.067 kg ai ha−1, respectively. Best ZHA treatments (0.29× to 0.30× IR herbicide rates + 0.74× to 0.80× BR herbicide rates) outperformed all reduced-rate broadcast herbicide treatments (0.25×, 0.5×, and 0.75×) based on net returns in partial budget analysis. Yields for highest yielding ZHA could not be distinguished from the 1× broadcast treatments in two of three site-years. Net returns due to herbicide application for the highest yielding ZHA were comparable with the 1× broadcast treatment in all three site-years. For the best ZHA, the 3-yr average for total herbicide applied per unit was 53% of the 1× broadcast rate. ZHA may provide row crop farmers with a new generic option for reducing herbicide rates and input costs while maintaining net returns and reducing the chance of surface water contamination by herbicides. Nomenclature: Atrazine; clopyralid; flumetsulam; glufosinate; metolachlor; giant foxtail, Setaria faberii (L.) Beauv. SETFA; common waterhemp, Amaranthus rudis Sauer AMATA; corn, Zea mays L., ‘Pioneer 33G28’.

Yellow Nutsedge (Cyperus esculentus) Control and Tuber Yield with Glyphosate and Glufosinate1

Greenhouse and field research was conducted to determine the effect of glufosinate, glyphosate, and glyphosate plus additional adjuvant on yellow nutsedge control and tuber production. Glyphosate at 0.84 kg/ha reduced yellow nutsedge dry weight 64%, whereas glufosinate at 0.4 kg/ha reduced dry weight only 22% when averaged over diammonium sulfate (DAS) and spray volume. Furthermore, yellow nutsedge dry weight was reduced 53% in the presence and 34% in the absence of DAS; however, dry weights were similar when spray volumes of glufosinate or glyphosate ranged from 140 to 1038 L/ha. Yellow nutsedge control with glyphosate and glufosinate increased to 88 and 68%, respectively, when the herbicides were injected into the plant. In the field, glufosinate at 0.4 kg/ha and glyphosate at 0.84 kg/ha controlled yellow nutsedge 19 and 53%, respectively. Glyphosate reduced yellow nutsedge tuber density 51%, tuber fresh weight 59%, and tuber sprouting 17% 42 wk after treatment in the field. The addition of nonionic surfactant, methylated seed oil, or crop oil concentrate to glyphosate plus DAS did not increase yellow nutsedge control with glyphosate in the greenhouse or field. Nomenclature: Crop oil concentrate; diammonium sulfate; dose–response; glufosinate; glyphosate; methylated seed oil; nonionic surfactant; yellow nutsedge, Cyperus esculentus L. #3 CYPES. Additional index words: Perennial weed, spray volume, tuber production. Abbreviations: COC, crop oil concentrate; DAS, diammonium sulfate ((NH4)2SO4); GR50, rate causing 50% growth reduction; MSO, methylated seed oil; NIS, nonionic surfactant; WAT, weeks after treatment.

Winter-Annual Weed Management in Corn (Zea mays) and Soybean (Glycine max) and the Impact on Soybean Cyst Nematode (Heterodera glycines) Egg Population Densities'

Field research was conducted at Columbia and Novelty, MO, to determine the impact of winter-annual weed management systems on corn and soybean grain yields, winter-annual weed control, and soybean cyst nematode (SCN) egg population densities over the crop production cycle. Corn grain yield was not affected by winter-annual weed management systems. Soybean grain yield was not affected by winter weed management systems in 2001, but at Columbia in 2002 winter rye and Italian ryegrass reduced soybean grain yield 62 and 64%, respectively. Fall-applied simazine + tribenuron in corn and chlorimuron + sulfentrazone in soybean controlled winter-annual weeds greater than 99%. Fall-overseeded winter rye and Italian ryegrass in corn and overseeded Italian ryegrass in soybean controlled winter weeds 66 to 86%. In the soybean studies, race 4 SCN population densities increased (P  =  0.08) in the nontreated control and remained stable (P  =  0.55) with fall-applied chlorimuron + sulfentrazone from fall 2001 to spring 2002 while SCN population densities were reduced (P  =  0.06) with spring-applied chlorimuron + sulfentrazone from fall 2002 to spring 2003. In the corn studies, none of the winter-annual weed management strategies reduced (P > 0.22) race 2 SCN population densities except winter rye from fall 2001 to spring 2002 (P  =  0.05). This research indicates that control of weed species considered to be weak alternative hosts for SCN affected SCN population densities some instances when race 4 SCN population densities were high in a continuous soybean production system or race 2 SCN population densities were low in a 2-yr corn production system. Nomenclature: Chlorimuron, sulfentrazone, simazine, tribenuron, common chickweed, Stellaria media (L.) Vill. #3 STEME, field pennycress, Thlaspi arvense L. # THLAR, henbit, Lamium amplexicaule L. # LAMAM, soybean cyst nematode, Heterodera glycines Ichinohe, corn, Zea mays L. ‘Asgrow RX740 RR’, Italian ryegrass, Lolium multiflorum L. ‘Marshall’, soybean, Glycine max (L.) Merr. ‘DK 38-52’, winter rye, Secale cereale L. ‘Forage Master’. Additional index words: Weed–nematode interaction, integrated pest management. Abbreviations: COC, crop oil concentrate.

Soil Quality of a Mature Alley Cropping Agroforestry System in Temperate North America

Long-term effects of alley cropping on soils in the temperate zone are not widely known. Management, landscape, and soil depth effects on soil physical and biological properties were examined in a silver maple (Acer saccharinum L.) no-till corn (Zea mays L.)- soybean (Glycine max L.) rotation established in 1990 in northeast Missouri. Soils from crop alleys and tree rows were collected along transects traversing upper to lower landscape positions at three depths. Fluorescein diacetate hydrolase (FDA), β-glucosidase, β-glucosaminidase, and dehydrogenase activities were measured. Soil bulk density, aggregate stability, carbon (C), nitrogen N), and enzyme activities decreased with soil depth in alley and tree rows except for glucosaminidase. Soil physical and biological parameters did not differ significantly between alley and tree row. Landscape position effects were not significant for management or depth. Tree establishment improves soil quality in the crop alley as the system matures with improvements extended throughout the soil profile.