Grasslands and Carbon: Processes and Trends

Grasslands, which make up 30% of the U.S. land surface, store significant amounts of carbon belowground in roots and soils. Learn how disturbances such as drought, grazing, fire and tillage can significantly impact the grassland carbon balance. Dr. Rebecca McCulley of the University of Kentucky, Dept. of Plant & Soil Sciences, talks about grasslands and the way they store and process carbon. Grasslands make up about 30 percent of the North American surface. Grasslands differ from forests in many ways, but from a carbon perspective they store a much greater proportion of the carbon than they take in in any given year in belowground components (roots and soil carbon pools). The best way to manage grasslands for carbon is to get the carbon below ground and keep it there. Disturbances such as drought, fire, grazing, and tillage are important in grasslands and can ultimately determine the carbon balance of these systems. You should gain an understanding of: How grasslands differ from forests in carbon storage. Methods for maximizing carbon storage in grassland systems (getting carbon into the soil and keeping it there). How disturbances such as drought, grazing, fire and tillage can significantly impact the grassland carbon balance

Cover Crops and Fertilization Alter Nitrogen Loss in Organic and Conventional Conservation Agriculture Systems

Agroecosystem nitrogen (N) loss produces greenhouse gases, induces eutrophication, and is costly for farmers; therefore, conservation agricultural management practices aimed at reducing N loss are increasingly adopted. However, the ecosystem consequences of these practices have not been well-studied. We quantified N loss via leaching, NH3 volatilization, N2O emissions, and N retention in plant and soil pools of corn conservation agroecosystems in Kentucky, USA. Three systems were evaluated: (1) an unfertilized, organic system with cover crops hairy vetch (Vicia villosa), winter wheat (Triticum aestivum), or a mix of the two (bi-culture); (2) an organic system with a hairy vetch cover crop employing three fertilization schemes (o N, organic N, or a fertilizer N-credit approach); and (3) a conventional system with a winter wheat cover crop and three fertilization schemes (o N, urea N, or organic N). In the unfertilized organic system, cover crop species affected NO3-N leaching (vetch \u3e bi-culture \u3e wheat) and N2O-N emissions and yield during corn growth (vetch, bi-culture \u3e wheat). Fertilization increased soil inorganic N, gaseous N loss, N leaching, and yield in the organic vetch and conventional wheat systems. Fertilizer scheme affected the magnitude of growing season N2O-N loss in the organic vetch system (organic N \u3e fertilizer N-credit) and the timing of loss (organic N delayed N2O-N loss vs. urea) and NO3-N leaching (urea \u3e\u3e organic N) in the conventional wheat system, but had no effect on yield. Cover crop selection and N fertilization techniques can reduce N leaching and greenhouse gas emissions without sacrificing yield, thereby enhancing N conservation in both organic and conventional conservation agriculture systems

Climate Change Extension: Presenting the Science is Necessary But Insufficient

Why Should We Consider How to Present Scientific Information? To engage a wide spectrum of agricultural producers in the discussion of human-induced climate change and its mitigation. What Did We Do? Our initial Extension efforts on climate change in Kentucky were based on an information-deficit model, which assumes that citizens fail to accept climate change because they don’t understand the science. However, social science research indicates that this topic has cultural significance for many agricultural producers, suggesting that presentation of sound scientific information alone is likely to be unpersuasive. Based on social science research, we redesigned our outreach efforts to emphasize: (1) more selective presentation of geophysical data; (2) positive messages as frequently as possible; and (3) messages that speak to core identities of citizens with diverse worldviews. What Have We Learned? Starting discussions on this sensitive topic are more successful if we make it clear to producers how much we appreciate their role in producing our food and, yes, in helping to reduce climate change. For example, U.S. producers deserve to be congratulated for the dramatic improvements made in agricultural productivity over the decades, since this has resulted in substantial reductions in carbon emissions when expressed per unit of production (per bushel, per gallon of milk, etc). We also point out practices they already do that help to reduce climate change, including energy-conservation measures and capturing biogas. Future Plans We plan to continue providing and refining our outreach on climate change, based on feedback from audiences and research from the social sciences. While we recognize that our current efforts may not quickly result in increased action on climate-change mitigation, our approach is designed to build acceptance of climate change as a topic deserving of the engagement of a wide range of citizens. Our working assumption is that promoting discussion on this highly divisive topic requires sensitivity to, and respect for, the diversity of worldviews held by Americans

Influence of the Neotyphodium--Tall Fescue Symbiosis on Belowground Processes

Much of the work to date on the relationships between cool season grasses and Neotyphodium fungal endophytes has focused on the physiological, biochemical, and genetic ramifications of the host-fungus relationship and the subsequent influence these effects have on ruminant nutrition, plant adaptation to environmental stresses, and aboveground ecological processes. Relatively little attention has been paid to effects on belowground parameters. In this paper, we review the research evaluating the impact of one endophyte-grass association, the Neotyphodium – tall fescue symbiosis, on underground ecological and biogeochemical processes. We also present some preliminary data showing that the quantity and nature of tall fescue root exudates are influenced by the plant cultivar and fungal genotype. This body of work clearly indicates that effects of the Neotyphodium-tall fescue symbiosis extend to belowground processes; however, additional research is needed to understand the mechanisms driving many of the observed root and soil endophyte effects

Effects of Long-Term Cattle Grazing and Woody Plant Encroachment on Soil Microbial Communities at the Santa Rita Experimental Range, Arizona

Livestock grazing is considered a key driver of woody plant encroachment in dryland ecosystems worldwide. Woody plant establishment in these systems creates “islands of fertility,” in part by modifying erosional processes such that soil and plant litter are deposited beneath the shrub canopy, creating a nutrient rich soil/litter matrix that supports enhanced soil microbial biomass pools. In this study, we utilized a long-term grazing exclosure (\u3e80 yrs) at the Santa Rita Experimental Range south of Tucson, Arizona and phopsholipid fatty acid analysis to quantify livestock grazing effects on soil microbial communities associated with the complex vegetative mosaic that characterizes these dryland systems (i.e., bare soil, grass patches, and trees). Consistent with previous studies, we found that total microbial biomass increased from bare soil, to grass patches, and was greatest near the bole under large, live trees. Ordination analysis of the most abundant fatty acids indicated that bare soil microbial communities differed from that of tree and grass-dominated areas, and these differences were more pronounced under large, live trees than small or dead trees. In the few instances where direct cattle grazing effects were observed, they occurred in soils associated with small, live trees. The fungal biomarker 18:2n6 was the only fatty acid with a significant effect of grazing: long-term grazing resulted in lower relative abundances of this fungal biomarker across all vegetation types. Our results suggest that direct effects of long-term grazing on soil microbial communities are less dramatic than the indirect effects of grazing. Alterations in the abundance of vegetation types and soil redistribution that often accompany grazing and woody plant encroachment are important drivers of soil microbial communities in these dryland systems

Effects of Climate Change on Pasture Production and Forage Quality

Why Study Climate Change and Pastures? Pastures cover more than 14 million hectares in the eastern half of the United States and support grazing animal and hay production while also contributing to the maintenance of overall environmental quality and ecosystem services. Climate change is likely to alter the function of these ecosystems. This manipulative field experiment evaluated the effect of warming and additional precipitation on forage production and quality. What Did We Do? We initiated a multi-factor climate change study, elevating air temperature (+3º C) and increasing growing season precipitation (+30% of long-term mean annual), in a central Kentucky pasture managed for hay production. Treatments began in May 2009 and have run continuously since. We measured the effects of warming and increased precipitation on pasture production, forage quality metrics, and for endophyte-infected tall fescue, ergot alkaloid concentrations. What Have We Learned? Effects of warming and increased precipitation on total yearly pasture production varied depending on the year of study; however, climate treatments never reduced production below that of the ambient control. Effects on forage quality metrics were relatively subtle. For endophyte-infected tall fescue, warming increased both ergovaline and ergovalinine concentrations (+40% of that in control ambient plots) throughout the study. These results indicate that central Kentucky pastures may be relatively resilient to future climate change; however, warming induced increases in ergot alkaloid concentrations in endophyte-infected tall fescue suggests that animal issues associated with fescue toxicosis are likely to be exacerbated under future climatic conditions. Future Plans We will continue this study for one more growing season and then destructively harvest it (in Fall 2013)

Impact of Climate Change on Wheat Production in Kentucky

Summary: From 2002 to 2012, Kentucky winter wheat ranged in value from $52 million to$209 million. Climate change and variability have the potential to significantly impact this important economic enterprise within our state. This report summarizes the current state of knowledge of the potential of climate change to impact wheat production in Kentucky and surrounding states

Does Fungal Endophyte Infection Improve Tall Fescue’s Growth Response to Fire and Water Limitation?

Invasive species may owe some of their success in competing and co-existing with native species to microbial symbioses they are capable of forming. Tall fescue is a cool-season, non-native, invasive grass capable of co-existing with native warm-season grasses in North American grasslands that frequently experience fire, drought, and cold winters, conditions to which the native species should be better-adapted than tall fescue. We hypothesized that tall fescue’s ability to form a symbiosis with Neotyphodium coenophialum, an aboveground fungal endophyte, may enhance its environmental stress tolerance and persistence in these environments. We used a greenhouse experiment to examine the effects of endophyte infection (E+ vs. E−), prescribed fire (1 burn vs. 2 burn vs. unburned control), and watering regime (dry vs. wet) on tall fescue growth. We assessed treatment effects for growth rates and the following response variables: total tiller length, number of tillers recruited during the experiment, number of reproductive tillers, tiller biomass, root biomass, and total biomass. Water regime significantly affected all response variables, with less growth and lower growth rates observed under the dry water regime compared to the wet. The burn treatments significantly affected total tiller length, number of reproductive tillers, total tiller biomass, and total biomass, but treatment differences were not consistent across parameters. Overall, fire seemed to enhance growth. Endophyte status significantly affected total tiller length and tiller biomass, but the effect was opposite what we predicted (E−\u3eE+). The results from our experiment indicated that tall fescue was relatively tolerant of fire, even when combined with dry conditions, and that the fungal endophyte symbiosis was not important in governing this ecological ability. The persistence of tall fescue in native grassland ecosystems may be linked to other endophyte-conferred abilities not measured here (e.g., herbivory release) or may not be related to this plant-microbial symbiosis

Biologic Cycling of Silica across a Grassland Bioclimosequence

The dynamics of biologic Si cycling in grassland ecosystems are largely unknown and likely to impact mineral weathering rates regionally and diatom productivity globally; key regulatory processes in the global Si cycle are closely tied to the global carbon cycle. Across a bioclimatic sequence spanning major grassland ecosystems in the Great Plains, soil biogenic silica depth distributions are similar to that of soil organic carbon; however, unlike soil organic carbon, quantities of soil biogenic silica decrease with increasing precipitation, despite an increase in annual biogenic inputs through litterfall across the same gradient. Though comprising only 1–3% of the total Si pool, faster turnover of biogenic Si and annual cycling by grasses should positively impact mineral dissolution. Our results suggest that the largest reservoir of biogenic Si in terrestrial ecosystems resides in soils, and emphasize the potential significance of grasslands in the global biogeochemical cycle of Si