Soil carbon saturation: a new model of soil organic matter stabilization and turnover

2006 Spring.Includes bibliographical referencesThe soil C saturation concept suggests an ultimate capacity of the soil to store C, dictating the rate and duration that soil may be effective in mitigating increasing atmospheric C02. This places a physicochemical limit on soil that is associated with textural, mineralogical and structural soil properties. This concept has been articulated in terms of four theoretical pools capable of C saturation: non-protected, physically- (micro-aggregate), chemically- (silt + clay), and biochemically-protected pools. My dissertation represents a multifaceted approach to examine C saturation in both whole soil and measurable soil fractions representing the four conceptual C pools. I evaluate the soil C saturation concept theoretically by modeling these relationships using published whole soil data, primary field data and through laboratory experiments. Analyses using published long-term soil C data from agroecosystem experiments suggested that within a given site, there was little support for models including C saturation, but when all sites were combined; there was strong support for the C saturation model. In general, published data were too sparse to adequately test individual sites. To evaluate the concept of C saturation for the four C pools, I used a three-part density, chemical, and physical fractionation scheme combined with modeling, using new data collected from eight agroecosystems in the US and Canada. I found that the chemically- and biochemically-protected pools showed strong evidence for C saturation, while the non-protected and physically-protected pools were non-saturating. In a 2.5 year laboratory experiment, I tested C stabilization rates and limits at two C addition rate to soils differing in soil C content and physicochemical characteristics. I found C saturation dynamics were most evident in the chemically-, biochemically- and some micro-aggregate protected C pools. I found greater C accumulation in the non-protected pool of the high C soil, suggesting C saturation of other pools. I conclude that SOC sequestration in many soils may be influenced by C saturation dynamics, impacting both decomposition kinetics and C stabilization. Soil C sequestration may be overestimated in models that do not account for C saturation dynamics

Long-term N fertilization and conservation tillage practices conserve surface but not profile SOC stocks under semi-arid irrigated corn

No tillage (NT) and N fertilization can increase surface soil organic C (SOC) stocks, but these gains are frequently not observed through the soil profile and could be subject to loss through subsequent tillage events. We evaluated a long-term irrigated continuous corn no-tillage (NT) and N rate study near Fort Collins, CO that was split into continuous NT or strip till (ST) treatments after five years. We measured grain and residue yields yearly, and SOC and particulate organic matter C (POM-C) at baseline, 5 yrs and 11 yrs later. Continuous NT depressed grain yields (10%) but not stover yields compared to ST. Continuous NT and increasing N fertilization rate increased surface (0–7.5 cm) SOC stocks 10 and 13%, respectively, compared to baseline. Seven years of ST completely negated initial surface (0–7.5 cm) SOC gain under NT and was only partially explained by POM-C loss (8–25%). All treatments lost between 14 and 19 Mg C ha−1 in the soil profile (0–120 cm) compared to baseline with no N or tillage effects. Soil C cycling appears to be rapid in this irrigated system, requiring greater C inputs to maintain SOC stocks. Effective conservation practices will need to balance crop yield, surface erosion protection, and profile-wide SOC stock losses

Adductor focal laryngeal Dystonia: correlation between clinicians’ ratings and subjects’ perception of Dysphonia

Background Although considerable research has focused on the etiology and symptomology of adductor focal laryngeal dystonia (AD-FLD), little is known about the correlation between clinicians’ ratings and patients’ perception of this voice disturbance. This study has five objectives: first, to determine if there is a relationship between subjects’ symptom-severity and its impact on their quality of life; to compare clinicians’ ratings with subjects’ perception of the individual characteristics and severity of AD-FLD; to document the subjects’ perception of changes in dysphonia since diagnosis; to record the frequency of voice arrest during connected speech; and, finally, to calculate inter-clinician reliability based on results from the Unified Spasmodic Dysphonia Rating Scale (USDRS) (Stewart et al, J Voice 1195-10, 1997). Methods Sixty subjects with AD-FLD who were receiving ongoing injections of BoNT participated in this study. Subjects’ mean age was 60.78 years and their mean duration of symptoms was 16.1 years. Subjects completed the Disease Symptom Questionnaire (DSQ) (specifically designed for this study) and the Voice Handicap Index-10 (VHI-10) (Jacobson et al, Am J Speech Lang Pathol 6:66–70, 1997) to measure the symptoms of their dysphonia and the impact of the disease on their quality of life. Two speech-language pathologists and two laryngologists used the Voice Arrest Measure (VAM) (specifically designed for this study) and the USDRS to independently rate voice recordings of 56/60 subjects. Results The mean VHI-10 score was 21.3 which is clinically significant. The results of the DSQ and the USDRS were highly correlated. The most severe symptoms identified by both subjects and clinicians were roughness, strain-strangled voice quality, and increased expiratory effort. Voice arrest, aphonia, and tremor were uncommon. Subjects rated their current voice quality at the time of reinjection (i.e., at the time of the study) as significantly better than at the time of their initial AD-FLD diagnosis (p < 0.0001). Inter-clinician reliability on the USDRS was significant at the 0.001 level. Conclusions The findings from the VHI-10 suggest that AD-FLD has a profound impact on quality of life. The results of the DSQ and the USDRS suggest that there is a strong correlation between subjects’ perception and clinicians’ assessment of the individual symptoms and the severity of the dysphonia. The findings from the VAM suggest that voice arrests are infrequent in subjects with AD-FLD who are receiving ongoing BoNT injections. The strong inter-clinician reliability on the USDRS suggests that it is an appropriate measure for identifying symptoms and severity of AD-FLD

N fertilizer and harvest impacts on bioenergy crop contributions to SOC

Below ground root biomass is infrequently measured and simply represented in models that predict landscape level changes to soil carbon stocks and greenhouse gas balances. Yet, crop-specific responses to N fertilizer and harvest treatments are known to impact both plant allocation and tissue chemistry, potentially altering decomposition rates and the direction and magnitude of soil C stock changes and greenhouse gas fluxes. We examined switchgrass (Panicum virgatum L.) and corn (Zea mays L.,) yields, below ground root biomass, C, N and soil particulate organic matter-C (POM-C) in a 9-year rain fed study of N fertilizer rate (0, 60, 120 and 180 kg N ha-1) and harvest management near Mead, NE, USA. Switchgrass was harvested with one pass in either August or postfrost, and for no-till (NT) corn, either 50% or no stover was removed. Switchgrass had greater below ground root biomass C and N (6.39, 0.10 Mg ha-1) throughout the soil profile compared to NT-corn (1.30, 0.06 Mg ha-1) and a higher below ground root biomass C:N ratio, indicating greater recalcitrant below ground root biomass C input beneath switchgrass. There was little difference between the two crops in soil POM-C indicating substantially slower decomposition and incorporation into SOC under switchgrass, despite much greater root C. The highest N rate decreased POM-C under both NT-corn and switchgrass, indicating faster decomposition rates with added fertilizer. Residue removal reduced corn below ground root biomass C by 37% and N by 48% and subsequently reduced POM-C by 22% compared to no-residue removal. Developing productive bioenergy systems that also conserve the soil resource will require balancing fertilization that maximizes above ground productivity but potentially reduces SOC sequestration by reducing below ground root biomass and increasing root and soil C decomposition

Long-term no-till and stover retention each decrease the global warming potential of irrigated continuous corn

Over the last 50 years, the most increase in cultivated land area globally has been due to a doubling of irrigated land. Long-term agronomic management impacts on soil organic carbon (SOC) stocks, soil greenhouse gas (GHG) emissions, and global warming potential (GWP) in irrigated systems, however, remain relatively unknown. Here, residue and tillage management effects were quantified by measuring soil nitrous oxide (N2O) and methane (CH4) fluxes and SOC changes (ΔSOC) at a long-term, irrigated continuous corn (Zea mays L.) system in eastern Nebraska, USA. Management treatments began in 2002, and measured treatments included no or high stover removal (0 or 6.8 Mg DM ha-1 yr-1, respectively) under no-till (NT) or conventional disk tillage (CT) with full irrigation (n = 4). Soil N2O and CH4 fluxes were measured for five crop-years (2011 to 2015), and ΔSOC was determined on an equivalent-mass basis to ~30 cm soil depth. Both area- and yield-scaled soil N2O emissions were greater with stover retention compared to removal and for CT compared to NT, with no interaction between stover and tillage practices. Methane comprise

N fertilizer and harvest impacts on bioenergy crop contributions to SOC

Below ground root biomass is infrequently measured and simply represented in models that predict landscape level changes to soil carbon stocks and greenhouse gas balances. Yet, crop-specific responses to N fertilizer and harvest treatments are known to impact both plant allocation and tissue chemistry, potentially altering decomposition rates and the direction and magnitude of soil C stock changes and greenhouse gas fluxes. We examined switchgrass (Panicum virgatum L.) and corn (Zea mays L.,) yields, below ground root biomass, C, N and soil particulate organic matter-C (POM-C) in a 9-year rain fed study of N fertilizer rate (0, 60, 120 and 180 kg N ha-1) and harvest management near Mead, NE, USA. Switchgrass was harvested with one pass in either August or postfrost, and for no-till (NT) corn, either 50% or no stover was removed. Switchgrass had greater below ground root biomass C and N (6.39, 0.10 Mg ha-1) throughout the soil profile compared to NT-corn (1.30, 0.06 Mg ha-1) and a higher below ground root biomass C:N ratio, indicating greater recalcitrant below ground root biomass C input beneath switchgrass. There was little difference between the two crops in soil POM-C indicating substantially slower decomposition and incorporation into SOC under switchgrass, despite much greater root C. The highest N rate decreased POM-C under both NT-corn and switchgrass, indicating faster decomposition rates with added fertilizer. Residue removal reduced corn below ground root biomass C by 37% and N by 48% and subsequently reduced POM-C by 22% compared to no-residue removal. Developing productive bioenergy systems that also conserve the soil resource will require balancing fertilization that maximizes above ground productivity but potentially reduces SOC sequestration by reducing below ground root biomass and increasing root and soil C decomposition

Does No-Tillage Mitigate Stover Removal in Irrigated Continuous Corn? A Multi-Location Assessment

No-tillage (NT) may ameliorate negative effects on soil properties from corn (Zea mays L.) stover harvest, but few long-term irrigated continuous corn production systems have been evaluated to test this hypothesis. We evaluated three long-term no-tillage sites (4–13 yr) in Nebraska and Colorado that spanned a range of precipitation and soil organic carbon (SOC) levels. We measured SOC, d13C of SOC, soil microbial biomass (SMB) and composition (i.e., phospholipid fatty acids, PLFAs), and water stable aggregation at all sites under stover retention vs. removal (~60%). Surface SOC stocks (0–30- cm depth) increased across the gradient and were 46.4, 57.4, and 63.1 Mg C ha–1 for Colorado, central Nebraska, and eastern Nebraska, respectively. Overall, residue removal decreased SOC stocks by 6% and soil aggregation by 12% in the 0- to 30-cm depth. The d13C signature of SOC indicated less new surface C storage under residue removal in Colorado, but not at the two Nebraska sites. Residue harvest did not decrease SMB or change soil microbial community structure, suggesting that high plant productivity buffered community composition from stover harvest impacts under NT but stimulated microbial activity levels that led to SOC loss. The high rates of stover removal used in this study decreased SOC stocks and aggregation at all sites compared to residue retained treatments, suggesting that no-tillage alone was not sufficient to maintain erosion protection and soil function

The effect of amblyopia treatment on stereoacuity

Purpose: To explore how stereoacuity changes in patients while they are being treated for amblyopia. Methods: The Monitored Occlusion Treatment for Amblyopia Study (MOTAS) comprised 3 distinct phases. In the first phase, baseline, assessments of visual function were made to confirm the initial visual and binocular visual deficit. The second phase, refractive adaptation, now commonly termed “optical treatment,” was an 18-week period of spectacle wear with measurements of logMAR visual acuity and stereoacuity with the Frisby test at weeks 0, 6, 12, and 18. In the third phase, occlusion, participants were prescribed 6 hours of patching per day. Results: A total of 85 children were enrolled (mean age, 5.1 ± 1.5 years). In 21 children amblyopia was associated with anisometropia; in 29, with strabismus; and in 35, with both. At study entry, poor stereoacuity was associated with poor visual acuity (P < 0.001) in the amblyopic eye and greater angle of strabismus (P < 0.001). Of 66 participants, 25 (38%) who received refractive adaptation and 19 (29%) who received occlusion improved by at least one octave in stereoacuity, exceeding test–retest variability. Overall, 38 (45%) improved one or more octaves across both treatment phases. Unmeasureable stereoacuity was observed in 56 participants (66%) at study entry and in 37 (43%) at study exit. Conclusions: Stereoacuity improved for almost one half of the study participants. Improvement was observed in both treatment phases. Factors associated with poor or nil stereoacuity at study entry and exit were poor visual acuity of the amblyopic eye and large-angle strabismus

Body Awareness: a phenomenological inquiry into the common ground of mind-body therapies

Enhancing body awareness has been described as a key element or a mechanism of action for therapeutic approaches often categorized as mind-body approaches, such as yoga, TaiChi, Body-Oriented Psychotherapy, Body Awareness Therapy, mindfulness based therapies/meditation, Feldenkrais, Alexander Method, Breath Therapy and others with reported benefits for a variety of health conditions. To better understand the conceptualization of body awareness in mind-body therapies, leading practitioners and teaching faculty of these approaches were invited as well as their patients to participate in focus groups. The qualitative analysis of these focus groups with representative practitioners of body awareness practices, and the perspectives of their patients, elucidated the common ground of their understanding of body awareness. For them body awareness is an inseparable aspect of embodied self awareness realized in action and interaction with the environment and world. It is the awareness of embodiment as an innate tendency of our organism for emergent self-organization and wholeness. The process that patients undergo in these therapies was seen as a progression towards greater unity between body and self, very similar to the conceptualization of embodiment as dialectic of body and self described by some philosophers as being experienced in distinct developmental levels