Recipient Organization
MONTANA STATE UNIVERSITY
(N/A)
BOZEMAN,MT 59717
Performing Department
Land Resources & Environmental Sciences
Non Technical Summary
Carbon. What is carbon, anyway, besides one element? Well, unlike R2D2, humans and soils are made of carbon!Carbon can be half (50%) or more of soil organic matter, whereas a human is only about 1/5 (20%) carbon. (Most of the rest of humans--about ½ to ¾--is plain old water; babies are 75% water and as we age, we dry out; Krulwich 2013).Speaking of water, soil organic matter works as a sponge in soils, holding water against the pull of gravity. Along with clays, soil organic matter is responsible for releasing all the water drawn up by every grass, tree, and crop root. Plants pump a lot of water out of soil and back into the air: hundreds of pounds of water for every pound of harvested, baled, or eaten plant parts. In fact, photosynthesizing plants are responsible for about one half of a globally important movement of carbon: from gas form (carbon dioxide) to solid form (as sugar or glucose). Their roots, and the microbes that feed off those sugars (together with you, the project reviewer), account for about the other half of the global carbon cycle: from solid forms back to gas forms (from glucose to carbon dioxide). This "ingassing" to the planet's plants and oceans (carbon dioxide into solid or liquid forms of carbon) is about balanced with the planet's roots and microbes (and humans) "outgassing" (from solid or liquid forms of carbon to gaseous forms of carbon); together, these transformations of carbon add up to about 200 gigatons of carbon per year. By comparison, human burning of solid and liquid and gaseous fossil fuels adds about 8 gigatons of carbon to the atmosphere every year. Only this relatively small addition is not balanced. This project explores ways that agricultural producers might help pull more carbon out of the atmosphere through their farm and ranch practices.So carbon is an essential ingredient in soil organic matter. One model from a "Virtual Mineral Museum" website (https://virtual-museum.soils.wisc.edu/display/soil-organic-matter/), for example, suggests that soil organic matter is exactly 54% carbon. Notice the fine print, however, which clarifies that "like snowflakes, ...no two soil organic molecules are alike."So how can soil organic matter levels be increased in soils? That is the focus of this proposal.Just like every bank account, the balance of carbon in soils reflects the balance of additions and losses. Too many withdrawals relative to deposits and your account dwindles to 0; if your deposits are greater than your withdrawals, your carbon balance increases.There are essentially only two ways to build soil organic matter in soil: invest in efforts to build carbon inputs while keeping carbon losses constant, or invest in efforts to keep carbon inputs even while reducing carbon losses. So to build carbon in soils, carbon 'deposits'--mostly through plant roots, which constantly leak 'sugar' into soil--must be greater than carbon 'withdrawals'--mostly through breathing by above- and belowground plant parts (shoots and roots) as well as the billions of microorganisms in every teaspoon of soil. Nearly every single one of the multitudes of living organisms across this planet breathe or respire. When humans and soils breathe, both convert sugars made of carbon (and hydrogen and oxygen, mostly) back into a gaseous form of carbon called carbon dioxide. Plants essentially reverse this part of the carbon cycle, converting gaseous carbon dioxide back into sugars through photosynthesis.The first part of this proposal looks at a sequence of soils in the Gallatin National Forest south of Bozeman formed from five very different rock types: gneiss, sandstone, shale (mudstone), limestone, and volcanic rock. We have measured how much soil carbon is in each of these soils; the shale soils hold about four times as much carbon as the sandstone soils. Less clear is how long, on average, that soil carbon lasts in the soil, or what we technically call a soil carbon residence time. So for this next iteration of this proposal, we will measure soil breath (the weight of carbon dioxide generated by the soil per unit area and per unit time) and use this soil carbon 'withdrawal' rate to better understand whether these mostly forested soils are gaining carbon, losing carbon, or have relatively stable soil carbon accounts. Using soil breathing rates from another Montana forest (Tenderfoot Creek Experimental Forest), we estimated soil carbon lasts between about 20 and 80 years, depending on the underlying rock type. The clayey shale soils had the longest-lasting soil carbon (~80 years), while the two sandiest soils overlying the gneiss and sandstone had the shortest lasting carbon. Using our banking analogy, this sequence of soils should help us understand differences in the withdrawal rates of carbon, since four of the five soils support stands of lodgepole pine forest, so the carbon inputs should be similar.The second part of this proposal looks at a small, long-term experiment in the Bangtail Mountains northeast of Bozeman where an MSU ecologist (Tad Weaver) has been turning over a set of meadow soils with a small spade at different frequencies: some soils have never been spaded, some soils have only been spaded once in the last 20 years, some soils have been spaded only every other year, and finally, some soils have been spaded every one of those 20 years. As with the rock sequence of soils, we will measure total soil carbon in each of these plots, as well as the soil breathing rates, to establish soil carbon residence times. This study should also help us understand the effects of disturbance on carbon withdrawal rates from these meadow soils, since prior studies have shown that soil disturbance (for example, by plowing) can produce large losses of carbon.The third part of this proposal will look at a sequence of three sites along the Interstate 90 highway that runs east-west past Bozeman. These sites were initially selected to run from the driest part of the Gallatin Valley near Three Forks (~4100 feet), past the Bear Canyon site (~4800 feet), up to the Bozeman Pass site (~5700 feet). At each site, 60 plots were established for the six treatments: control, 6-inch mow, 12-inch mow, transplanted nitrogen-fixing legumes into pre-existing grass-dominated plots, transplanted legumes into cleared plots, and transplanted woody shrubs into grass-dominated plots. At each plot, we measured soil organic matter. This study will help us better understand how the management of roadside vegetation will influence the balance of soil carbon 'deposits' (legumes or shrubs or existing grasses) versus 'withdrawals' (via mowing and soil breath).The last part of this proposal looks at a long-term experimental agricultural site near Amsterdam where a wheat farmer (together with MSU researchers) is trying to improve his carbon balance and his yields by alternating his wheat crops with different combinations of cover crops, from taprooted (radish) to fibrous-rooted (oat) to nitrogen-fixing (peas) to mustard-like plants (canola). Soil organic matter levels are approximately 2% near the surface and decline rapidly with depth. There do not appear to be large differences in how long soil carbon lasts in these plots (~15 years), perhaps because this experiment has only been underway since 2012.Just because carbon is essentially out-of-sight doesn't mean it should be out of mind.
Animal Health Component
33%
Research Effort Categories
Basic
33%
Applied
33%
Developmental
34%
Goals / Objectives
This MAES proposal has four subobjectives that align with the goals and objectives introduced earlier:Develop innovative approaches to measurements of local and regional soil carbon stocksDevelop innovative approaches to measurements of local soil carbon fluxes, with a special focus on soil respiration fluxesDevelop innovative approaches for scaling sCaRTs from local to regional scalesEffective dissemination of findingsThrough this work, I will improve dissemination of evidence-based knowledge; adoption, testing, and refinement of management practices with a high probability of lengthening sCaRTs; and develop formative and summative evaluation tools to assess overall research program effectiveness.We lack a clear mechanistic understanding of the factors that control soil organic matter accretion, mineralization, and composition. In addition, while there is little debate over the potential societal value of terrestrial carbon sequestration as a stabilization wedge (Pacala and Socolow 2004), there is much more debate over best practices for measuring the effectiveness of sequestration approaches. Terrestrial sequestration involves the manipulation of photosynthetic pathways to transform atmospheric carbon into soil organic matter, but quantifying increases in soil carbon stocks (nevermind predicting the persistence of any additional sequestered carbon; Schmidt et al. 2011) is challenging at best (Oades 1988, Wendt and Hauser 2013).Recent MAES-related research by MSU colleagues (Engel et al. 2017) has shown, for example, that 10 years of no-till, cover-crop-cocktail approaches to sequestering soil organic carbon (SOC) yielded mixed, but very subtle, results. In 2002, at the Arthur Post Farm just west of Bozeman, average SOC levels were about 37 megagrams per hectare to a depth of 30 cm (37 Mg C/ha*0.3 m). In 2012, after 10 years of six, distinct, no-till, annual crop management practices, average SOC levels ranged from 35 to 38 Mg C/ha*0.3 m. A seventh annual cropping management practice, including annual tillage, yielded average SOC levels of 34 Mg C/ha*0.3 m. In other words, the differences were subtle. Perhaps not as subtle as the proverbial "needle-in-a-haystack" that some folks equate to odds of 1 in 1 billion, but subtle nonetheless.In fact, expressed as grams per cubic foot of soil per year (or, since 1 paper clip weighs about 1 gram,paper clips per cubic foot of soil per year), the difference between the no-till, wheat-wheat rotation and the initial levels of C was a little more than 1 paper clip per cubic foot of soil per year. (For reference, a surface 1 cubic foot block of this Post Farm soil would weigh 70 to 90 pounds, or between 32,000 and 41,000 grams or paperclips.) The tilled, wheat-wheat rotation yielded lower carbon levels: about 2.5 paper clips of carbon less per cubic foot of soil per year. These are quite subtle results given the investment reflected in 10 years of continued crop management and initial and end-of-project monitoring!And, unfortunately, none of these results speak to the overall persistence of that carbon. Will the 1 additional paper clip of carbon gain per cubic foot of soil per year persist for 1, 10, or 100 years?Thus, the overall research question for this MAES project is "What are the dominant controls over soil carbon residence times?" This work will clarify regional soil carbon stocks and fluxes. This understanding, in tum, should improve local, regional, national, and international approaches to mitigating and adapting to climate change (UNEP 2013).
Project Methods
There are four principal components to quantifying sCaRTs using a state factor approach:a. A lithosequence approach to sCaRTs, employing an unparalleled local gradient;b. A chronosequence approach to sCaRTs, tracking how soil carbon dynamics might reflect time since disturbance;c. A "climo"/biosequence approach (Roadside Project); andd. A biosequence approach to sCaRTs, taking advantage of a long-term cover crop cocktail research project at Amsterdam, MT.The disturbance sequence is intended to characterize sCaRTs as a function of disturbance such as tillage. Recent work by Schmidt et al. (2011) is a reminder of the complexities inherent in soil carbon turnover rates. Soil organic matter mean residence times range from <10 years to as high as 300 years, highlighting variability and inability of molecular structures to explain long residence times, except for fire-derived organic matter. More recent work (Kallenbach et al. 2016) implies most soil organic matter is likely of microbial origin.First, I introduce methods common to both the lithosequence and climosequence approaches.Soil carbon stocks. For all these state factor approaches, traditional soil characterization techniques (Schoeneberger et al. 2012) will be employed to quantify soil carbon stocks. Soil carbon consists of numerous broad categories of carbon, from particulate inorganic carbon (e.g., limestone gravels), to dissolved inorganic carbon (e.g., HCO3-), to particulate organic carbon (e.g., woody roots), to dissolved organic carbon, to geogenic organic carbon (e.g., coal; Ussiri et al. 2014). This project will focus on particulate organic carbon stocks, and will quantify these stocks as the product of soil organic carbon concentrations (units: mg SOC [g soil]-1), soil bulk density (units: g soil [cm3 soil]-1), adjusting for (subtracting) coarse fragment (>2 mm) content.Determination of soil carbon stocks boils down to obtaining a weight from a volume, as areas--by definition--cannot be assigned a density. Thus, the depth of soil stocks will be a crucial element of this part of the study. Perhaps an even more crucial element, however, will be how soils representing identical volumes, but non-identical masses, are compared (Wendt and Hauser 2013, Engel et al. 2017).Soil carbon fluxes. For this MAES project, I will focus on gaseous losses of carbon from soils, using a Licor 8100A infrared gas analyzer that can be used for field measurements of soil CO2 fluxes, with units of micromoles of CO2 per square meter per second. Repeated measurements across seasons enable an estimation of annual respiration losses, which can be converted into units such as g CO2-C m-2 y-1. This instrument can be multiplexed (manifolded) to up to 16 individual chambers, enabling high-temporal resolution measurements of soil gas fluxes within a radius of ~15 m of the analyzer. I am developing protocols with the assistance of undergraduate students for quality control procedures associated with these measurements. For this proposal specifically, we are interested in developing protocols for "water-induced soil and plant root respiration rates" (WISPRRR), where rates are recorded immediately before and immediately after the addition of a standard volume of water.Calculation of sCaRT. The quotient of a volumetric estimate of soil carbon stock (g C m-2, to a specified depth) and an estimate of annual soil respiration fluxes (g CO2-C m-2 y-1) yields a soil carbon residence time (y). For just one example, it is possible to estimate the sCaRT of Montana State University campus soils. These soils have been mapped as the Blackmore series, which has a soil organic matter concentration of 5% in the uppermost 25 cm, an oven-dry bulk density of 1.2 g cm-3, and a surface coarse fragment content of 0%.Assuming soil organic matter is double soil organic carbon(SOC) means your next walk across campus will be a walk across ~7500 g SOC m-2 or ~20 pounds of SOC per square yard or ~2 pounds of SOC per square foot.I have not measured soil respiration rates on campus, but summer values for control plots at Towne's Harvest Garden averaged ~10 µmol CO2 m-2 s-1 during Summer 2013. Assuming annualized values are approximately one-third this value (~3 µmol CO2 m-2 s-1) to account for reduced fluxes during the Winter, Spring, and Fall seasons yields the following estimation of annual soil respiration from campus soils: ~1130 g CO2-C m-2 y-1. The soil carbon residence time--the quotient of campus stocks to this flux, therefore, would be: 7500 g SOC m-2 / 1130 g C m-2 y-1 = 6.6 years.As soil respiration losses from soils (denominator) are reduced, sCaRT increase. For example, if soil respiration losses are only 0.5 µmol CO2 m-2 s-1 over the course of a year, then annualized C fluxes would drop to ~190 g CO2-C m-2 y-1, yielding a sCaRT of ~40 years, a six-fold increase. The sensitivity of sCaRT to both the depth of interest for estimating soil carbon stocks as well as the annualized soil respiration estimates will be a focus of this MAES research.My interest with climosequence approaches to sCaRTs is to identify a series of soils that can provide an analogue to turning an effective precipitation dial from a drier setting to a wetter setting. One climosequence approach--tailored to Montana--extends Gallatin Valley work by Weaver (1978). I do not envision a sealevel-to-summit climate gradient, as exploited elegantly across the Sierra Nevada Range in California (Dahlgren et al. 1997) or Kohala Volcano in Hawaii (Chadwick et al. 2003). Instead, my interest in a climosequence is more aligned with an effective precipitation gradient that brackets thresholds, as has been demonstrated for African savannas (e.g., Khomo et al. 2013).One of the ecological thresholds that is of primary interest for this MAES proposal is the rain-snow transition across the elevational gradient represented by the Bridger Mountains (Weaver 1978). This transition appears to have no influence on base cation saturation, the fraction of a soil's cation exchange complex occupied by base cations such as Ca2+, Mg2+, K+, or Na+, but only across the Bridger Mountains, not the Sierra Nevada, where a linear decline in base saturation is evident. Three of these base cations (excepting Na+) represent critical plant macronutrients, and thus constitute an important index of soil fertility. (There is no rain-snow transition across the Hawaiian climosequence, as Kohala Volcano is not sufficiently high to experience sustained snows, unlike other volcanoes on the Big Island. Instead, a threshold decline in base saturation appears to occur where effective precipitation yields soil water inputs just greater than 1 pore volume; Chadwick et al. 2003.)The Sierra Nevada work implies orographic increases in precipitation, coupled to a shift from liquid to frozen precipitation (e.g., snow), coupled to decreased evaporation and transpiration as a function of well-established adiabatic lapse rate relationships, together lead to increased effective precipitation, and this increase is manifest in replacement of base cations on the cation exchange complex by acid cations such as H+ or Al3+.