• Authors:
    • Adams,H. D.
    • Collins,A. D.
    • Briggs,S. P.
    • Vennetier,M.
    • Dickman,L. T.
    • Sevanto,S. A.
    • Garcia-Forner,N.
    • Powers,H. H.
    • McDowell,N. G.
  • Source: Global Change Biology
  • Volume: 21
  • Issue: 11
  • Year: 2015
  • Summary: Higher temperatures associated with climate change are anticipated to trigger an earlier start to the growing season, which could increase the terrestrial C sink strength. Greater variability in the amount and timing of precipitation is also expected with higher temperatures, bringing increased drought stress to many ecosystems. We experimentally assessed the effects of higher temperature and drought on the foliar phenology and shoot growth of mature trees of two semiarid conifer species. We exposed field-grown trees to a ~45% reduction in precipitation with a rain-out structure ('drought'), a ~4.8 °C temperature increase with open-top chambers ('heat'), and a combination of both simultaneously ('drought+heat'). Over the 2013 growing season, drought, heat, and drought+heat treatments reduced shoot and needle growth in pinon pine ( Pinus edulis) by ≥39%, while juniper ( Juniperus monosperma) had low growth and little response to these treatments. Needle emergence on primary axis branches of pinon pine was delayed in heat, drought, and drought+heat treatments by 19-57 days, while secondary axis branches were less likely to produce needles in the heat treatment, and produced no needles at all in the drought+heat treatment. Growth of shoots and needles, and the timing of needle emergence correlated inversely with xylem water tension and positively with nonstructural carbohydrate concentrations. Our findings demonstrate the potential for delayed phenological development and reduced growth with higher temperatures and drought in tree species that are vulnerable to drought and reveal potential mechanistic links to physiological stress responses. Climate change projections of an earlier and longer growing season with higher temperatures, and consequent increases in terrestrial C sink strength, may be incorrect for regions where plants will face increased drought stress with climate change.
  • Authors:
    • Ashworth,A. J.
    • West,C. P.
    • Allen,F. L.
    • Keyser,P. D.
    • Weiss,S. A.
    • Tyler,D. D.
    • Taylor,A. M.
    • Warwick,K. L.
    • Beamer,K. P.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: Biological N 2 fixation (BNF) via legume intercrops can provide an alternative to inorganic N fertilizer and thereby minimize the economic and environmental costs of bioenergy feedstock and forage production. The objectives of this study were to (i) verify switchgrass ( Panicum virgatum L.) as a non-N 2-fixing reference plant for distinguishing between soil- and atmosphere-derived N; (ii) determine BNF levels via the 15N enrichment method for one cool-season legume (red clover [ Trifolium pratense L.]) and three warm-season legumes ([partridge pea] [ Chamaecrista fasciculate Michx.], sunn hemp [ Crotalaria juncea L.], and pigeonpea [ Cajanus cajan (L.) Millsp.]) when intercropped into switchgrass and a near relative, guineagrass ( Panicum maximum L.); and (iii) evaluate the validity of the N-difference method by comparing it against the 15N enrichment technique in humid temperate and semiarid tropical climates. The results revealed little difference in the N assimilation rates of legume and non-N 2-fixing reference plants, suggesting that switchgrass is an appropriate reference species. Annual fixation for red clover was greatest, followed by partridge pea, and lastly sunn hemp in temperate systems (87, 84, and 35 kg ha -1, respectively), all of which tended to supply greater amounts of N in subsequent seasons. Considerably greater BNF occurred in tropical intercrop systems (exceeding 240 kg ha -1). Consequently, the BNF of selected legumes approximates or exceeds recommended N fertilizer rates (67 kg N ha -1) in both humid temperate and semiarid tropical pasture and feedstock systems. The N-difference method did not provide estimates for BNF that were comparable to 15N-enrichment-derived values ( P>0.05).
  • Authors:
    • Bailey,Rebecca R.
    • Butts,Thomas R.
    • Lauer,Joseph G.
    • Laboski,Carrie A. M.
    • Kucharik,Christopher J.
    • Davis,Vince M.
  • Source: Weed Science
  • Volume: 63
  • Issue: 4
  • Year: 2015
  • Summary: Nitrous oxide (N2O) is a potent greenhouse gas with implication for climate change. Agriculture accounts for 10% of all greenhouse gas emissions in the United States, but 75% of the country's N2O emissions. In the absence of PRE herbicides, weeds compete with soybean for available soil moisture and inorganic N, and may reduce N2O emissions relative to a weed-free environment. However, after weeds are killed with a POST herbicide, the dead weed residues may stimulate N2O emissions by increasing soil moisture and supplying carbon and nitrogen to microbial denitrifiers. Wider soybean rows often have more weed biomass, and as a result, row width may further impact how weeds influence N2O emissions. To determine this relationship, field studies were conducted in 2013 and 2014 in Arlington, WI. A two-by-two factorial treatment structure of weed management (PRE + POST vs. POST-only) and row width (38 or 76 cm) was arranged in a randomized complete block design with four replications. N2O fluxes were measured from static gas sampling chambers at least weekly starting 2 wk after planting until mid-September, and were compared for the periods before and after weed termination using a repeated measures analysis. N2O fluxes were not influenced by the weed by width interaction or width before termination, after termination, or for the full duration of the study at P <= 0.05. Interestingly, we observed that POST-only treatments had lower fluxes on the sampling day immediately prior to POST application (P = 0.0002), but this was the only incidence where weed influenced N2O fluxes, and overall, average fluxes from PRE + POST and POST-only treatments were not different for any period of the study. Soybean yield was not influenced by width (P = 0.6018) or weed by width (P = 0.5825), but yield was 650 kg ha(-1) higher in the PRE + POST than POST-only treatments (P = 0.0007). These results indicate that herbicide management strategy does not influence N2O emissions from soybean, and the use of a PRE herbicide prevents soybean yield loss. Nomenclature: Soybean; Glycine max (L.) Merr.
  • Authors:
    • Beach,R. H.
    • Cai,Y.
    • Thomson,A.
    • Zhang,X.
    • Jones,R.
    • McCarl,B. A.
    • Crimmins,A.
    • Martinich,J.
    • Cole,J.
    • Ohrel,S.
    • Deangelo,B.
    • McFarland,J.
    • Strzepek,K.
    • Boehlert,B.
  • Source: Environmental Research Letters
  • Volume: 10
  • Issue: 9
  • Year: 2015
  • Summary: Increasing atmospheric carbon dioxide levels, higher temperatures, altered precipitation patterns, and other climate change impacts have already begun to affect US agriculture and forestry, with impacts expected to become more substantial in the future. There have been numerous studies of climate change impacts on agriculture or forestry, but relatively little research examining the long-term net impacts of a stabilization scenario relative to a case with unabated climate change. We provide an analysis of the potential benefits of global climate change mitigation for US agriculture and forestry through 2100, accounting for landowner decisions regarding land use, crop mix, and management practices. The analytic approach involves a combination of climate models, a crop process model (EPIC), a dynamic vegetation model used for forests (MC1), and an economic model of the US forestry and agricultural sector (FASOM-GHG). We find substantial impacts on productivity, commodity markets, and consumer and producer welfare for the stabilization scenario relative to unabated climate change, though the magnitude and direction of impacts vary across regions and commodities. Although there is variability in welfare impacts across climate simulations, we find positive net benefits from stabilization in all cases, with cumulative impacts ranging from $32.7 billion to $54.5 billion over the period 2015-2100. Our estimates contribute to the literature on potential benefits of GHG mitigation and can help inform policy decisions weighing alternative mitigation and adaptation actions. © 2015 IOP Publishing Ltd.
  • Authors:
    • Blanco-Canqui,H.
    • Shaver,T. M.
    • Lindquist,J. L.
    • Shapiro,C. A.
    • Elmore,R. W.
    • Francis,C. A.
    • Hergert,G. W.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: Cover crops (CCs) can provide multiple soil, agricultural production, and environmental benefits. However, a better understanding of such potential ecosystem services is needed. We summarized the current state of knowledge of CC effects on soil C stocks, soil erosion, physical properties, soil water, nutrients, microbial properties, weed control, crop yields, expanded uses, and economics and highlighted research needs. Our review indicates that CCs are multifunctional. Cover crops increase soil organic C stocks (0.1-1 Mg ha -1 yr -1) with the magnitude depending on biomass amount, years in CCs, and initial soil C level. Runoff loss can decrease by up to 80% and sediment loss from 40 to 96% with CCs. Wind erosion potential also decreases with CCs, but studies are few. Cover crops alleviate soil compaction, improve soil structural and hydraulic properties, moderate soil temperature, improve microbial properties, recycle nutrients, and suppress weeds. Cover crops increase or have no effect on crop yields but reduce yields in water-limited regions by reducing available water for the subsequent crops. The few available studies indicate that grazing and haying of CCs do not adversely affect soil and crop production, which suggests that CC biomass removal for livestock or biofuel production can be another benefit from CCs. Overall, CCs provide numerous ecosystem services (i.e., soil, crop-livestock systems, and environment), although the magnitude of benefits is highly site specific. More research data are needed on the (i) multi-functionality of CCs for different climates and management scenarios and (ii) short- and long-term economic return from CCs.
  • Authors:
    • Rhinhart, K.
    • Machado, S.
    • Ghimire, R.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: Intensive cultivation of native grassland for dryland agriculture continuously depleted soil organic carbon (SOC) and nutrients. In 2010, we evaluated the influence of 80 yr of crop residue and nutrient management practices on SOC and N in 0- to 60-cm soil depth profiles in conventionally tilled winter wheat ( Triticum aestivum L.)-summer fallow (WW-SF) system. Residue and N treatments, no N addition with fall burning (FB0), spring burning (SB0), and no burning (NB0), 45 kg N ha -1 with SB (SB45) and NB (NB45), 90 kg N ha -1 with SB (SB90) and NB (NB90), manure (MN, 5.32 Mg dry mass ha -1 yr -1), and pea vines (PV, 0.99 Mg dry mass ha -1 yr -1), were in ordered arrangement, and an undisturbed grassland (GP) was used as a reference. All WW-SF treatments had less SOC and N stocks than GP. The SOC stocks were lowest under FB0 with 50% less SOC than GP. The WW-SF treatments have depleted up to 63 and 26% of SOC and N from surface soil since 1931. Fall burning and MN treatments depleted SOC at rates of 0.64 and 0.17 Mg ha -1 yr -1. Nitrogen stocks decreased at a rate of 0.02 Mg ha -1 yr -1 in FB, SB, and NB treatments, and 0.01 Mg ha -1 yr -1 in PV treatment. Reduction in tillage, application of low C/N ratio residues, and elimination of burning can improve sustainability of winter wheat production in the summer fallow region of the Pacific Northwest (PNW).
  • Authors:
    • Duniway, M. C.
    • Munson, S. M.
    • Bradford, J. B.
    • Gremer, J. R.
  • Source: Primary Research Article
  • Volume: 21
  • Issue: 11
  • Year: 2015
  • Summary: Climate change predictions include warming and drying trends, which are expected to be particularly pronounced in the southwestern United States. In this region, grassland dynamics are tightly linked to available moisture, yet it has proven difficult to resolve what aspects of climate drive vegetation change. In part, this is because it is unclear how heterogeneity in soils affects plant responses to climate. Here, we combine climate and soil properties with a mechanistic soil water model to explain temporal fluctuations in perennial grass cover, quantify where and the degree to which incorporating soil water dynamics enhances our ability to understand temporal patterns, and explore the potential consequences of climate change by assessing future trajectories of important climate and soil water variables. Our analyses focused on long-term (20-56 years) perennial grass dynamics across the Colorado Plateau, Sonoran, and Chihuahuan Desert regions. Our results suggest that climate variability has negative effects on grass cover, and that precipitation subsidies that extend growing seasons are beneficial. Soil water metrics, including the number of dry days and availability of water from deeper (>30 cm) soil layers, explained additional grass cover variability. While individual climate variables were ranked as more important in explaining grass cover, collectively soil water accounted for 40-60% of the total explained variance. Soil water conditions were more useful for understanding the responses of C 3 than C 4 grass species. Projections of water balance variables under climate change indicate that conditions that currently support perennial grasses will be less common in the future, and these altered conditions will be more pronounced in the Chihuahuan Desert and Colorado Plateau. We conclude that incorporating multiple aspects of climate and accounting for soil variability can improve our ability to understand patterns, identify areas of vulnerability, and predict the future of desert grasslands.
  • Authors:
    • Haudenshield, J. S.
    • Bowen, C. R.
    • Hartman, G. L.
    • Fox, C. M.
    • Cary, T. R.
    • Diers, B. W.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: Diseases and pests of soybean [ Glycine max (L.) Merr.] often reduce soybean yields. Targeted breeding that incorporates known genes for resistance and non-targeted breeding that eliminates susceptible plants in breeding populations reduces the impact of soybean pathogens and pests. Maturity group (MG) III soybean cultivars released from 1923 through 2008 were grown in three field environments to determine if disease and insect ratings were associated with year of cultivar release. Disease and pest ratings were evaluated on 40 soybean cultivars at one location (Urbana, IL) planted in two rotation treatments in 2010 and on 59 cultivars in two locations (Urbana and Arthur) in 2011. During the season, foliar disease symptoms and insect foliar feeding damage were recorded. At harvest maturity, stem diseases were assessed. In at least one environment, foliar incidence reached 100% for bacterial diseases, brown spot ( Septoria glycines Hemmi), and insect foliar feeding damage and 100% incidence for anthracnose [ Colletotrichum truncatum (Schwein.) Andrus & W.D. Moore], Cercospora stem blight ( Cercospora kikuchii T. Matsumoto & Tomoy.), and charcoal rot [ Macrophomina phaseolina (Tassi) Goid.] on stems for all cultivars. For the nine different disease and pest severity assessments in 2010, seven had a significant ( P<0.05) negative correlation to year of cultivar release indicating that cultivars more recently released had lower severity ratings than cultivars with older release dates. This study demonstrated that incidence and severity of diseases were less pronounced on more newly-released soybean cultivars, showing that decades of breeding has resulted in increased disease resistance in modern soybean cultivars.
  • Authors:
    • Baer, S. G.
    • Bello, N. M.
    • Knapp, M.
    • Morgan, T. J.
    • Bryant, J.
    • DeLaCruz, A.
    • Tetreault, H.
    • Olsen, J. T.
    • Johnson, L. C.
    • Maricle, B. R.
  • Source: Original Article
  • Volume: 8
  • Issue: 7
  • Year: 2015
  • Summary: Identifying suitable genetic stock for restoration often employs a best guess' approach. Without adaptive variation studies, restoration may be misguided. We test the extent to which climate in central US grasslands exerts selection pressure on a foundation grass big bluestem (Andropogon gerardii), widely used in restorations, and resulting in local adaptation. We seeded three regional ecotypes of A.gerardii in reciprocal transplant garden communities across 1150km precipitation gradient. We measured ecological responses over several timescales (instantaneous gas exchange, medium-term chlorophyll absorbance, and long-term responses of establishment and cover) in response to climate and biotic factors and tested if ecotypes could expand range. The ecotype from the driest region exhibited greatest cover under low rainfall, suggesting local adaptation under abiotic stress. Unexpectedly, no evidence for cover differences between ecotypes exists at mesic sites where establishment and cover of all ecotypes were low, perhaps due to strong biotic pressures. Expression of adaptive differences is strongly environment specific. Given observed adaptive variation, the most conservative restoration strategy would be to plant the local ecotype, especially in drier locations. With superior performance of the most xeric ecotype under dry conditions and predicted drought, this ecotype may migrate eastward, naturally or with assistance in restorations.
  • Authors:
    • Tanaka, D.
    • Nichols, K.
    • Schmer, M.
    • Archer, D.
    • Hendrickson, J.
    • Liebig, M.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: Cover crops can expand ecosystem services, though sound management recommendations for their use within semiarid cropping systems is currently constrained by a lack of information. This study was conducted to determine agroecosystem responses to late-summer seeded cover crops under no-till management, with particular emphasis on soil attributes. Short-term effects of late-summer seeded cover crops on soil water, available N, near-surface soil quality, and residue cover were investigated during three consecutive years on the Area IV Soil Conservation Districts Research Farm near Mandan, ND. Mean aboveground cover crop biomass was highly variable across years (1430, 96, and 937 kg ha -1 in 2008, 2009, and 2010, respectively), and was strongly affected by precipitation received within 14 d following cover crop seeding. During years with appreciable biomass production (2008 and 2010), cover crops significantly reduced available N in the 0.9-m depth the following spring ( P=0.0291 and 0.0464, respectively). Cover crop effects on soil water were subtle, and no differences in soil water were found between cover crop treatments and a no cover crop control before seeding cash crops the following spring. Late-summer seeded cover crops did not affect near-surface soil properties or soil coverage by residue. Soil responses to late-summer seeded cover crops did not differ between cover crop mixtures and monocultures. Late-summer seeded cover crops may enhance ecosystem services provided by semiarid cropping systems through biomass production and N conservation, though achieving these benefits in a consistent manner appears dependent on timely precipitation following cover crop seeding.