Urea is frequently surface applied to winter wheat (Triticum aestivum L.) during cold weather months (October–April) in the semiarid northern Great Plains. This study was conducted to quantify NH3 ...volatilization loss from surface-applied urea (100 kg N ha−1) and urea amended with N-(n-butyl) thiophosphoric triamide (NBPT) during this period. Ammonia emissions were quantified by a micrometeorological integrated horizontal flux method with samplers placed on a mast in the center of circular plots (20-m radius). Cumulative NH3 losses from urea varied but averaged 20.5% of applied N across 12 trials. The largest losses (30–44% of applied N) occurred after urea was applied to high-water-content soil surfaces, followed by a period of slow drying with little or no precipitation. Emissions occurred for a prolonged period often lasting >42 d. Periods (1–2 wk) of high NH3 flux (>30 g N ha−1 h−1) frequently occurred when mean daily soil temperatures (1-cm depth) were –2 to 5°C. In one trial, 24.3% of applied N was lost after urea was applied to a 140-mm snowpack. Ammonia losses were moderated by applying urea to dry soil surfaces. If precipitation events that followed were light (<8 mm), losses were reduced to 10 to 20% of applied N. If the events were heavy (>18 mm), then losses were <10%. Coating urea with NBPT (1 g kg−1) reduced cumulative NH3 losses by 66%. Volatilization protection lasted 2 to 3 wk on acidic soils, and >7 wk on an alkaline soil. This study demonstrated that significant NH3 losses from surface-applied urea could occur during cold weather months.
Recently completed NH3 volatilization field studies with urea suggest the urease inhibitor N‐(n‐butyl) thiophosphoric triamide (NBPT) has prolonged activity in alkaline relative to acidic soils. A ...laboratory incubation experiment was conducted at two temperatures (0.5 and 20°C) to determine whether NBPT degradation was affected by soil pH (alkaline vs. acidic) and to determine the impact on urea hydrolysis. Soil (10 g) from the surface horizon of a loam (pH 5.5) and a silt loam (pH 8.4) was placed in bottles and incubated up to 28 d in constant‐temperature chambers. A third soil was constructed by adding CaCO3 (0.3 g) to the loam soil (pH 8.2). Urea (20 mg) with and without NBPT (20 mg) was applied to each soil. High‐performance liquid chromatography–mass spectrometry analysis of KCl extracts revealed that NBPT degraded rapidly in the acidic soil compared with the alkaline soils (silt loam and loam with added CaCO3). Exponential decay constants for the acidic soil were 5.2 and 3.9 times larger than decay constants for the alkaline soils at 0.5 and 20°C, respectively. Urea hydrolysis rates were reduced by NBPT, and the response was greater for the alkaline soils (P < 0.0001). Hydrolysis was inhibited by 17.0 and 86.2% at 20°C and by 53.3 and 92.1% at 0.5°C for the acidic and alkaline soils, respectively. This study confirmed field observations that NBPT persistence and activity is greater in alkaline soils. Additional studies, including chemical hydrolysis and sorption, are needed to clarify the processes responsible for the rapid disappearance of NBPT from extracts of acidic soils.
Urea placement in band or nests has been shown to enhance N use efficiency, but limited work has been done to assess its affect on N2O emissions. This study compared N2O emissions from urea prills ...applied to an Amsterdam silt loam (fine‐silty, mixed, superactive, frigid Typic Haplustolls) using broadcast, band, and nest placements. Experiments were conducted in greenhouse pots (200 kg N ha−1) and in canola (Brassica rapa L.) seeded fields using rates of 100 kg N ha−1 (recommended) and 200 kg N ha−1 Urea placement affected N2O emission patterns and cumulative N2O losses in the greenhouse and field. Urea prills placed in nests, and sometimes bands delayed N2O production with peak flux activity occurring later, and elevated emission activity being more prolonged than for broadcast applications. Differences were more obvious at 200 kg N ha−1 These effects were attributed to a delay in urea hydrolysis and inhibition of nitrification. The fraction of applied urea‐N lost as N2O for broadcast, band, and nest placements applied at the recommended rate averaged 2.0, 2.7, and 5.8 g N kg−1 N, respectively. The fraction of applied urea‐N lost as N2O averaged 2.9, 10.4, and 9.2 g N kg−1 N for broadcast, band, and nest placements when urea‐N rate was increased from 100 to 200 kg N ha−1, respectively. Greater N2O production with nest placement may in part be due to significant soil NO2–N accumulations. Potential benefits to crop fertilizer use efficiency that come with placement of urea in concentrated zones may lead to enhanced N2O production.
Field measurements of N2O emissions from soils are limited for cropping systems in the semiarid northern Great Plains (NGP). The objectives were to develop N2O emission-time profiles for cropping ...systems in the semiarid NGP, define important periods of loss, determine the impact of best management practices on N2O losses, and estimate direct N fertilizer-induced emissions (FIE). No-till (NT) wheat (Triticum Aestivum L.)-fallow, wheat-wheat, and wheat-pea (Pisum sativum), and conventional till (CT) wheat-fallow, all with three N regimes (200 and 100 kg N ha-1 available N, unfertilized control); plus a perennial grass-alfalfa (Medicago sativa L.) system were sampled over 2 yr using vented chambers. Cumulative 2-yr N2O emissions were modest in contrast to reports from more humid regions. Greatest N2O flux activity occurred following urea-N fertilization (10-wk) and during freeze-thaw cycles. Together these periods comprised up to 84% of the 2-yr total. Nitrification was probably the dominant process responsible for N2O emissions during the post-N fertilization period, while denitrification was more important during freeze-thaw cycles. Cumulative 2-yr N2O-N losses from fertilized regimes were greater for wheat-wheat (1.31 kg N ha-1) than wheat-fallow (CT and NT) (0.48 kg N ha-1), and wheat-pea (0.71 kg N ha-1) due to an additional N fertilization event. Cumulative losses from unfertilized cropping systems were not different from perennial grass-alfalfa (0.28 kg N ha-1). Tillage did not affect N2O losses for the wheat-fallow systems. Mean FIE level was equivalent to 0.26% of applied N, and considerably below the Intergovernmental Panel on Climate Change mean default value (1.25%).
Large ungulates grazing native rangelands during winter must balance forage intake, a source of energy gain, with minimizing thermal stress, a source of energy loss. Another source of energy loss, ...energy expended, is related to time spent in different activities. Natural or man-made shelter may alter time spent in different activities. Our objectives were to determine if access to windbreaks altered diurnal activity patterns of beef cattle grazing a windy, foothill range site during winter, and if diurnal activity patterns could be related to weather. We observed diurnal activity patterns of cattle with and with out access to windbreaks (windbreak, nonwindbreak) for two winters on an exposed pasture in southwest Montana. Actual use of windbreaks was only recorded in Winter 2. Windbreak cattle did not use the windbreak until day 16; subsequently, time spent behind windbreaks ranged from 0 to 30%. Activity patterns of windbreak and nonwindbreak cattle differed in subtle ways, indicating they used similar behaviors to minimize energy expended and to maximize energy gain. Time spent grazing was inconsistent between the two winter trials, possibly reflecting large differences in body condition when they entered each winter. For individual groups, time spent grazing (Winter 1, 33-96%; Winter 2, 18-94%) and standing (Winter 1, 0-63%; Winter 2, 0-78%) varied widely on a day-to-day basis, reflecting either an immediate response to that day's weather, or possibly a compensatory response to the previous day’(s’) weather, especially following cold, windy days. Wind velocity had minimal effect on grazing time, presumably because high wind velocities were associated with relatively warm days, or the animals were in sufficient condition to tolerate high wind velocities. Instead of minimizing energy expended by lying down during extreme cold, cattle spent more time standing, which maximizes heat gain from solar radiation. During winter, cattle behavior is a tradeoff between maximizing energy gain (thermal and food) and minimizing energy loss (thermal and metabolic).
Two Eurasian forbs,
Euphorbia esula L. and
Centaurea maculosa Lam., continue to spread in the northwestern United States despite extensive and expensive control efforts. We investigated whether ...litter from these forbs and associated soils suppress germination and growth of two native perennial grasses (
Pseudoroegneria spicata Scribn. & Smith A. Love,
Pascopyrum smithii Rydb. A. Love), which may partly explain the success of these invasive forbs. Seed germination was unaffected, but roots were shorter at higher leachate concentrations. The physical presence of litter (
Euphorbia,
Centaurea, none) did not affect seed germination or number of leaves of seedlings of the four species, but it affected seedling heights; the tallest seedlings were those covered with
Centaurea litter; the shortest were those without litter. As a mechanical barrier, litter type did not affect survival or number of leaves of pregerminated seeds, but litter inhibited shoot growth. Seed germination of the four species on soils from infested or noninfested areas differed;
Euphorbia germination, albeit low (< 4 %) was higher on soils collected from
Euphorbia- infested areas, whereas germination of the other species was higher on soils from noninfested areas. These results indicate that litter from these invasive forbs can have subtle effects on growth of seedlings of these native grasses, especially the native
Pseudoroegneria, and that these forbs have some unknown effect on soil properties which reduce germination.
Die Ausbreitung zweier Unkräuter eurasiatischer Herkunft (
Euphorbia esula L. und
Centaurea maculosa Lam.) in den nordwestlichen USA konnte trotz umfangreicher Gegenmaßnahmen bisher nicht aufgehalten werden. Wir untersuchten, ob diese Kräuter durch Streuproduktion oder andere Bodenveränderungen eine negative Wirkung auf Keimfähigkeit und Wachstum zweier heimischer mehrjähriger Gräser (
Pseudoroegneria spicata Scribn. & Smith A. Love,
Pascopyrum smithii Rydb. A. Love) ausüben, was zum Teil den Erfolg dieser Unkräuter erklären könnte. Saataufgang war nicht beeinträchtigt, aber Wurzeln waren kürzer und wiesen höhere Exsudatkonzentrationen auf. Die pure Anwesenheit von
Euphorbia- oder
Centaurea streu hatte keinen Effekt auf Auflauf oder Blattanzahl der Sämlinge aller vier Arten, sowohl auf Böden aus verunkrauteten Arealen als auch auf vorher unkrautfreien Böden. Streu beeinflusste aber die Sämlingshöhe: die höchsten Sämlinge traten in Verbindung mit
Centaurea Streu auf, die niedrigsten unter streulosen Bedingungen. Die Streuart hatten keinen Einfluss auf Überlebensfähigkeit oder Blattzahl vorgekeimter Samen, jedoch beeinträchtigte das Vorhandensein von Streu die Sprosslänge. Die Keimfähigkeit der vier Arten hing davon ab, ob die Böden aus verunkrauteten oder unkrautfreien Gebieten stammten. Die
Euphorbia-Keimrate, obwohl generell niedrig (< 4 %), war höher auf Böden aus
Euphorbia-befallenen Gebieten, die Keimfähigkeit der anderen Arten war höher auf Böden aus unkrautfreien Arealen. Unsere Resultate zeigen, dass Streu dieser eingeschleppten Kräuter leichte Effekte auf das Keimlingswachstum der beiden heimischen Gräser ausübt, insbesondere auf die heimische
Pseudoroegneria und dass diese Käuter die Bodeneigenschaften in bisher unbekannter Weise beeinflussen, welche die Keimungsrate beeinträchtigen.
The diagnostic utility of functional analyses has been demonstrated with a variety of behaviors including tics. Whereas previous analyses have focused on the discovery of maintaining variables to aid ...in treatment prescription, we employed a functional analysis to confirm a clinical diagnosis. An 11 year old male student, who had not been previously diagnosed with a tic disorder, exhibited multiple vocal tic-like behaviors which had persisted over a period of time. Teacher reports conflicted regarding the possible etiology of these behaviors. Hence, a functional analysis was conducted in the classroom to determine if the behaviors were maintained by operant variables. Our hypothesis stated that the occurrence of vocal behaviors across experimental conditions would strongly indicate the presence of a tic disorder. The functional analysis included the following conditions: attention, escape, alone, freeplay, and high sensory stimulation. We used a multi-element design to evaluate the effects of the different stimulus conditions on vocal-behavior frequency. Data indicated the student exhibited vocal behaviors in all conditions. However, the behaviors were partially exacerbated in the attention and escape conditions. Results supported the diagnosis of a transient tic disorder affected by operant variables.
Herbivores develop preferences for certain plant species in several ways. One way is to learn from role models, another is through postingestive feedback. In this study we determined (1) whether ...yearling sheep exposed to leafy spurge (
Euphorbia esula L.) as lambs graze it more readily than yearlings that were not exposed to it as lambs, and (2) whether this difference, if present, persists through the grazing season. On a leafy spurge-infested, Idaho fescue (
Festuca idahoensis Elmer) range site, we compared the grazing behavior of naive groups of Targhee yearlings with grazing behavior of experienced groups for 3 years. Using focal animals, we assessed diet selectivity by counting bites and by determining time spent grazing different forage types. During the grazing season, nutritive value (crude protein, neutral detergent fiber, in vitro dry matter digestibility) of leafy spurge was always higher than nutritive value of Idaho fescue. Experienced yearlings spent more than four times as much time grazing leafy spurge in early summer compared with naive yearlings (averaged across 1992 and 1993, experienced 13.6% vs. naive 2.9%), whereas in mid- (39% vs. 31%) and late summer (37% vs. 38%) both groups spent similar amounts of time grazing leafy spurge. Neither group readily grazed the plant in early summer. Experienced yearlings had higher bite rates of leafy spurge than naive yearlings during the early summer sampling periods in 1992 and 1993 (averaged across 1992 and 1993, 15.9 vs. 5.0 bites min
−1) but their bite rates were similar by mid-summer (22.7 vs. 20.6 bites min
−1). In 1994, we observed their grazing behavior every 5 days for 35 days. Initially, naive yearlings spent less time grazing leafy spurge than experienced yearlings, but were spending similar amounts of time grazing leafy spurge by day 25. Previous experience with leafy spurge, compared with no experience, resulted in a slight but short-lived advantage in early summer use of the species. Within 3–4 weeks, sheep that had never previously been exposed to leafy spurge readily grazed the plant.
Livestock may impact habitat quality for grasshoppers by reducing food availability and by altering microclimate and potential oviposition sites. A 5-year study was conducted to create consistent ...grazing impacts on replicated plots and measure their effects on plant cover, microclimate, and grasshopper abundance. Cattle were used to produce two levels of grazing intensity that were compared to ungrazed controls. Differences in plant cover were greatest immediately after grazing each summer, grasshopper microhabitats tending to be shadier, cooler, less windy, and more humid in the ungrazed plots. The grasshopper assemblage included five of the worst pest grasshopper species in North America:
Ageneotettix deorum,
Aulocara elliotti,
Melanoplus sanguinipes,
M. packardii, and
Camnula pellucida. Most species had greater abundance on ungrazed pastures, particularly during the 4–6 weeks after grazing each year. However,
A. elliotti was often more abundant in heavily grazed areas early in the year when early instars were present and in late summer when adults were predominant. There was no strong evidence that the effect of grazing on grasshopper abundance increased over the 5-year study. At this time, all changes in grasshopper numbers cannot be directly attributed to particular habitat characteristics that changed after grazing, but the results suggest that grazing management could be used to reduce pest grasshopper densities.
PDF
