Keith R. Harmoney

Quantifying drylands' drought resistance and recovery: the importance of drought intensity, dominant life history and grazing regime

Projected global change will increase the level of land-use and environmental stressors such as drought and grazing, particularly in drylands. Still, combined effects of drought and grazing on plant production are poorly understood, thus hampering adequate projections and development of mitigation strategies. We used a large, cross-continental database consisting of 174 long-term datasets from >30 dryland regions to quantify ecosystem responses to drought and grazing with the ultimate goal to increase functional understanding in these responses. Two key aspects of ecosystem stability, resistance to and recovery after a drought, were evaluated based on standardized and normalized aboveground net primary production (ANPP) data. Drought intensity was quantified using the standardized precipitation index. We tested effects of drought intensity, grazing regime (grazed, ungrazed), biome (grassland, shrubland, savanna) or dominant life history (annual, perennial) of the herbaceous layer to assess the relative importance of these factors for ecosystem stability, and to identify predictable relationships between drought intensity and ecosystem resistance and recovery. We found that both components of ecosystem stability were better explained by dominant herbaceous life history than by biome. Increasing drought intensity (quasi-) linearly reduced ecosystem resistance. Even though annual and perennial systems showed the same response rate to increasing drought intensity, they differed in their general magnitude of resistance, with annual systems being ca. 27% less resistant. In contrast, systems with an herbaceous layer dominated by annuals had substantially higher postdrought recovery, particularly when grazed. Combined effects of drought and grazing were not merely additive but modulated by dominant life history of the herbaceous layer. To the best of our knowledge, our study established the first predictive, cross-continental model between drought intensity and drought-related relative losses in ANPP, and suggests that systems with an herbaceous layer dominated by annuals are more prone to ecosystem degradation under future global change regimes.

Effects of Grazing Pressure on Efficiency of Grazing on North American Great Plains Rangelands

Abstract Comparisons of stocking rates across sites can be facilitated by calculating grazing pressure. We used peak standing crop and stocking rates from six studies in the North American Great Plains (Cheyenne, Wyoming; Cottonwood, South Dakota; Hays, Kansas; Nunn, Colorado; Streeter, North Dakota; and Woodward, Oklahoma) to calculate a grazing pressure index and develop relationships for harvest efficiency, utilization, grazing efficiency, and animal performance and production. Average grazing pressures for heavy, moderate, and light stocking across the study sites were 40, 24, and 14 animal unit days · Mg−1, respectively. These grazing pressures resulted in average harvest efficiency values of 38%, 24%, and 14% and grazing efficiencies of 61%, 49%, and 39% for heavy, moderate, and light stocking rates, respectively. Utilization increased quadratically as grazing pressure index increased, whereas grazing and harvest efficiencies exhibited a linear increase with grazing pressure. The latter indicates that nonlivestock forage losses (e.g., weathering, senescence, wildlife, insects) were disproportional across stocking rates. Average daily gain of livestock decreased linearly as grazing pressure index increased across study sites. Prediction equations reaffirm assumptions of 50% grazing efficiency and 25% harvest efficiency associated with moderate stocking. Novel here, however, is that harvest and grazing efficiencies increased at high grazing pressures and decreased at low grazing pressures. Use of grazing pressure index to “standardize” stocking rates across rangeland ecosystems in the North American Great Plains should improve communication among scientists, resource managers, and the public, and thus better achieve both production and conservation goals on these lands.

Nitrogen and harvest management of Conservation Reserve Program (CRP) grassland for sustainable biomass feedstock production

The Biomass Regional Feedstock Partnership has identified grasslands planted under the Conservation Reserve Program (CRP) as a potential source for herbaceous bioenergy feedstock. The goal of this project is to assess the yield potential of CRP grasslands across diverse regions. Consistent with that goal, the objective of this project was to establish yield potential and quality parameters for several different CRP grasslands, representative of different growing environments. Standard field scale agricultural practices were used as management guidelines at each location. The test locations were identified and established based on known regions containing concentrated tracts of CRP grassland and represented variable climatic parameters and production histories. Biomass production potential for CRP land dominated by either warm‐ or cool‐season grass mixtures in each location was evaluated over the course of three growing seasons (2008, 2009, and 2010). Specifically, a mixture of warm‐season perennial grasses was evaluated in North Dakota, Kansas, and Oklahoma, while a cool‐season mixture was evaluated in Montana, Georgia, and Missouri. Maximum biomass yields for the three warm‐season CRP sites ranged from 4.0 to 7.2 Mg ha−1 and for the three cool‐season CRP sites 3.4–6.0 Mg ha−1. Our results demonstrate that CRP grassland has potential as a bioenergy feedstock resource if the appropriate management practices are followed.

Herbicide effects on established yellow old world bluestem (Bothriochloa ischaemum).

Nine herbicides were tested in a field trial during 2001 and 2002 for the ability to suppress growth of established plants of yellow old world bluestem (OWB) that had invaded native vegetation in central Kansas. Herbicide treatments were applied to OWB at the V4 stage of growth using the Nebraska staging method. At 9 wk after treatment (WAT), plots treated with imazapyr at 1.40 kg ai/ ha had much lower OWB plant frequency than the untreated plots, and plots sprayed with imazapyr and bromacil at 7.84 kg ai/ha had much lower OWB tiller densities than the control plots. Imazapyr and glyphosate at 3.36 kg ai/ha provided greater OWB control than other herbicides. At the first frost after treatment application, imazapyr and bromacil treatments continued to have lower OWB frequency and tiller density than the control plots. Visible herbicide control was closely related to end-of-season yield (R = −0.97). Imazapic at 0.16 kg ai/ha, glyphosate, sulfometuron at 0.21 kg ai/ ha, bromacil, and imazapyr controlled OWB from 54 to 94%. Split applications, altered timing of herbicide application, or varied rates of herbicides that exhibited suppressive potential may further improve efficacy of these herbicides. Nomenclature: Bromacil; glyphosate; imazapic; imazapyr; sulfometuron; yellow bluestem, Bothriochloa ischaemum (L.) Keng #3 DIHIS. Additional index words: Biomass, frequency, native vegetation, old world bluestem, suppression, tiller density. Abbreviations: CRP, conservation reserve program; OWB, old world bluestem; WAT, weeks after treatment.

Suppression of Caucasian Old World Bluestem with Split Application of Herbicides

Caucasian old world bluestem (OWB), seeded for conservation and forage production, has escaped into rangelands in the southern and central Great Plains. Glyphosate, imazapic, imazapyr, imazethapyr, and sulfometuron methyl herbicides were applied at the four- to five-leaf stage and again 8 wk later in 2003 and 2005 to control Caucasian OWB. Glyphosate at 1.14 kg ai/ha at each application was the only treatment that reduced frequency and tiller density of Caucasian OWB, and also controlled over 80% of growth, at 6 wk after the first treatment (WAT) both years. After the first autumn frost, plots treated with glyphosate and imazapyr at 0.28 kg ai/ha at each application had lower frequency and much greater suppression of Caucasian OWB growth than plots treated with other herbicides. Tiller densities and seedhead densities were also less in plots treated with glyphosate and imazapyr compared to other herbicides and the nontreated control. Biomass at the end of the season was near zero for plots treated with glyphosate and imazapyr in 2003, and 26 to 46% of the nontreated control biomass in 2005. Frequency of Caucasian OWB the year following treatment was less than 5% for both glyphosate and imazapyr. Broadcast application of glyphosate and imazapyr also controlled remnant native vegetation in plots, thus different application methods, such as ropewick application, may be useful to avoid native grass injury. Nomenclature: Glyphosate, imazapic, imazapyr, imazethapyr, >sulfometuron methyl, Caucasian old world bluestem, Bothriochloa bladhii Retz (S.T. Blake) BOTBL

Comparative Morphology of Caucasian Old World Bluestem and Native Grasses

Caucasian old world bluestem (OWB) [Bothrichloa bladhii (Retz) S.T. Blake] has been widely introduced in the southern and central Great Plains as a perennial warm-season grass for forage and soil conservation. As a result of its widespread introduction, it has escaped into some native rangelands. Once established in native pastures, observations suggest that Caucasian OWB may mature earlier than native vegetation and may be avoided by grazing animals in mixed rangelands, thus altering grazing distribution and over utilizing native species. More advanced morphological development in grasses is also associated with lower forage quality and lower palatability. This study was conducted to examine if morphological development of Caucasian OWB and native perennial warm-season grass species differs. Monoculture stands of Caucasian OWB, big bluestem (Angropogon gerardii Vitman), little bluestem [Schizachyrium scoparium (Michx.) Nash], and side-oats grama [Bouteloua curtipendula (Michx.) Torr.] were established in the spring of 2000. After the initiation of first growth in 2002 and 2003, vegetation was hand clipped each week for 8 wk and quantified for morphological stage of development according to the Nebraska staging method. In 2002, a drought season, Caucasian OWB had a greater mean stage weight (MSW) than the native species during Weeks 3 through 7 (P < 0.001). In 2003, Caucasian OWB began the season at a similar morphological stage as the native species, but had a rate of development that was 5 to 11 times greater than the native species. The last 3 wk of the sampling period, MSW of Caucasian OWB was greater than all three native species (P < 0.001). With more advanced morphological development in Caucasian OWB than the native grasses, declining forage quality could affect grazing preference and distribution patterns in mixed swards of Caucasian OWB and native species. The introduction of Caucasian OWB into native rangelands may have impacts that have yet to be understood.

Alfalfa Production with Subsurface Drip Irrigation in the Central Great Plains

Irrigated alfalfa production is gaining interest because of the growing number of dairies in the semi-arid U.S. Central Great Plains and its longstanding superior profitability compared to other alternative crops grown in the region. Irrigation requirements for alfalfa are great because of alfalfa’s long growing season, so it is important that irrigation be utilized efficiently in this region where water is pumped from the declining Ogallala aquifer. A three-year yield study (2005-2007) was conducted at the Kansas State University Northwest Research-Extension Center in Colby, Kansas, to evaluate production of subsurface drip irrigated alfalfa on a deep productive silt loam soil. Three irrigation levels (randomized complete block design of three replications) designed to replace 70%, 85%, or 100% of the calculated crop evapotranspiration minus precipitation were compared in terms of alfalfa yield, irrigation amount, plant-available soil water, crop water use, and crop water productivity. Alfalfa yield was also evaluated at three perpendicular horizontal distances from the 1.5 m spaced driplines (0, 0.38, and 0.76 m). Annual alfalfa yields were unaffected by irrigation level, averaging 20.8 Mg ha-1 while irrigation amounts averaged 396, 484, and 586 mm for the 70%, 80%, and 100% ET irrigation levels, respectively. Seasonal crop water use was significantly greater with increased irrigation, but only by an average difference of 137 mm among irrigation levels as compared to the 190 mm difference in irrigation amount. Crop water productivity was significantly greater with decreased levels of irrigation, with values of 23.5, 22.0, and 20.4 kg ha-1 mm-1 for the 70%, 85%, and 100% ET irrigation levels, respectively. No significant differences existed in alfalfa yield with respect to horizontal perpendicular distance from the dripline with the exception of the 0.76 m distance, which yielded less in the drier and warmer year 2006. Large and significant decreases in alfalfa yield and crop water productivity occurred with successive harvests, with the first harvest having 272% and 196% of the fifth harvest yield and crop water productivity, respectively. Plant-available soil water decreased as the season progressed for all irrigation levels, but to a much greater extent for the 70% ET level, averaging at the time of the fifth seasonal harvest only 41% and 54% of the soil water for the 85% and 100% ET irrigation levels, respectively. These large seasonal decreases in soil water for the 70% ET irrigation level would be anticipated to be of even greater concern in extended multiple-year drought periods. This fact coupled with the 102 mm reduction in seasonal irrigation amount for the 85% ET irrigation level compared to the 100% ET irrigation level leads to a recommendation of scheduling replacement of 85% of the ET minus precipitation when subsurface drip irrigating alfalfa in the Central Great Plains. This study was conducted in a region with deep silt loam soils where approximately 60% of the average annual precipitation occurs during the summer months. Additionally, 125 mm of fall irrigation was applied during the dormant fall season to reduce root intrusion and rodent damage. These combined facts need to be considered when applying the results of this study to other regions and when using different irrigation management strategies.

Effects of a New Herbicide (Aminocyclopyrachlor) on Buffalograss and Forbs in Shortgrass Prairie

Abstract Herbicides used to control many forb species in pastures may injure desirable native grass species. Buffalograss, a major component of shortgrass rangeland, often is injured by some growth regulator herbicides, such as 2,4-D and dicamba. Aminocyclopyrachlor (formerly known as DPX-MAT28 and herein termed ACPCR), a new synthetic auxin herbicide chemistry for control of broadleaf weeds, was investigated for injury to buffalograss and control of forbs in shortgrass prairie at varying rates of application. In the season of application, ACPCR at rates of 140 g ai ha−1 or less caused buffalograss injury that was either negligible or short-lived, and visual estimates of grass injury were 8% or less at the end of the growing season. At ACPCR rates of 280 g ha−1, more injury was evident at 3 wk after treatment (WAT) than at the end of the season if adequate precipitation was available for new leaf growth. When precipitation was lacking, evidence of injury persisted through to the end of the season when treated at the greatest rate of ACPCR. Buffalograss injury was mainly in the form of browned leaf tips, but total buffalograss dry matter yield was not different between any treatments in either year. The year after treatment, no buffalograss injury was evident from any of the herbicide rates. Final forb control was 97% or greater each year for ACPCR at the 140 and 280 g ha−1 rates. In this experiment, rates as low as ACPCR at 140 g ha−1 provided excellent forb control and maintained buffalograss productivity. Nomenclature: 2,4-D; aminocyclopyrachlor; dicamba; buffalograss, Bouteloua dactyloides (Nutt.) J.T. Columbus BUCDA.

Combining Glyphosate With Burning or Mowing Improves Control of Yellow Bluestem (Bothriochloa ischaemum)

Abstract The invasive yellow bluestem (Bothriochloa ischaemum [L.] Keng) threatens native biodiversity, and its control is of interest to land managers involved in restoration of invaded grasslands. We used single, double, and triple applications of glyphosate (2.125 kg ai · ha−1 · application−1) over the course of one growing season in combinations at different timings (early, middle, late season) with and without a mechanical treatment of mowing or burning to determine the most effective control method. One year after treatment, burning and mowing prior to a mid-season single or double early, middle, and/or late season herbicide application resulted in a similar level of control of yellow bluestem relative to a triple herbicide application, all of which had greater control relative to herbicide treatment alone. Reproductive tiller density and visual obstruction increased 2 yr after treatment with two herbicide treatments applied either early and middle season or early and late season, but it was prevented with burning and mowing prior to herbicide application. With the exception of three herbicide applications, combining burning or mowing with herbicide applications provided more effective control of yellow bluestem than any individual herbicide applications. Burning or mowing likely improves glyphosate effectiveness by altering the invasive grass structure so that plants are clear of standing dead and have shorter, active regrowth to enhance herbicide effectiveness. During restoration projects requiring control of invasive yellow bluestem, an effective management option is a combination of mechanical and chemical control.

Growth and reproductive performance of beef replacement heifers fed development diets containing soybean meal or wet distillers grains 1

ABSTRACT Our objective was to evaluate the effects of replacing soybean meal with wet distillers grains plus solubles (WDG) in beef heifer development diets on growth and reproductive performance. Weaned heifers (n = 172; initial BW 319 ± 2 kg; age 282 ± 1 d) were stratified by BW and age and assigned randomly to be fed development diets using soybean meal (CON) or WDG as the primary source of CP in the diet. Heifers were allotted equally to 8 pens, adapted to diets for 14 d, and fed for ad libitum intake for 94 d. Heifer BW was measured on d 28, 56, and 84 relative to the beginning of the experiment and at breeding; paired serum samples were collected at these times to define puberty status. After 94 d, treatments were combined in a native short- grass rangeland pasture. Heifers from each treatment were exposed to ovulation synchronization and fixed-time AI 23 or 51 d after diets ended. Total DM delivered was 4,695 kg less (P 0.10). Conception to fixed-time AI and overall pregnancy rates were not different (P > 0.60) between treatments. Under the conditions of our study, developing replacement heifer diets using WDG as the primary source of CP had negative temporal effects on growth performance and age at puberty; however, these effects were nullified when heifers were allowed to graze native range for at least 23 d before breeding.