abstract: Drylands (arid and semi-arid grassland ecosystems) cover about 40% of the Earth's surface and support over 40% of the human population, most of which is in emerging economies. Human development of drylands leads to topsoil loss, and over the last 160 years, woody plants have encroached on drylands, both of which have implications for maintaining soil viability. Understanding the spatial variability in erosion and soil organic carbon and total nitrogen under varying geomorphic and biotic forcing in drylands is therefore of paramount importance. This study focuses on how two plants, palo verde (Parkinsonia microphylla, nitrogen-fixing) and jojoba (Simmondsia chinensis, non-nitrogen fixing), affect sediment transport and soil organic carbon and total nitrogen pools in a dryland environment north of Phoenix, Arizona. Bulk samples were systematically collected from the top 10 cm of soil in twelve catenae to control for the existence and type of plants, location to canopy (sub- or intercanopy, up- or downslope), aspect, and distance from the divide. Samples were measured for soil organic carbon and total nitrogen and an unmanned aerial system-derived digital elevation map of the field site was created for spatial analysis. A subset of the samples was measured for the short-lived isotopes 137Cs and 210Pbex, which serve as proxy erosion rates. Erosional soils were found to have less organic carbon and total nitrogen than depositional soils. There were clear differences in the data between the two plant types: jojoba catenae had higher short-lived isotope activity, lower carbon and nitrogen, and smaller canopies than those of palo verde, suggesting lower erosion rates and nutrient contributions from jojoba plants. This research quantifies the importance of biota on influencing hillslope and soil dynamics in a semi-arid field site in central AZ and finishes with a discussion on the global implications for soil sustainability. / Dissertation/Thesis / Masters Thesis Geological Sciences 2018

abstract: Rangelands are an extensive land cover type that cover about 40% of earth’s ice-free surface, expanding into many biomes. Moreover, managing rangelands is crucial for long-term sustainability of the vital ecosystem services they provide including carbon (C) storage via soil organic carbon (SOC) and animal agriculture. Arid rangelands are particularly susceptible to dramatic shifts in vegetation cover, physical and chemical soil properties, and erosion due to grazing pressure. Many studies have documented these effects, but studies focusing on grazing impacts on soil properties, namely SOC, are less common. Furthermore, studies testing effects of different levels of grazing intensities on SOC pools and distribution yield mixed results with little alignment. The primary objective of this thesis was to have a better understanding of the role of grazing intensity on arid rangeland soil C storage. I conducted research in long established pastures in Jornada Experimental Range (JER). I established a 1500m transect in three pastures originating at water points and analyzed vegetation cover and SOC on points along these transects to see the effect of grazing on C storage on a grazing gradient. I used the line-point intercept method to measure and categorize vegetation into grass, bare, and shrub. Since soil adjacent to each of these three cover types will likely contain differing SOC content, I then used this vegetation cover data to calculate the contribution of each cover type to SOC. I found shrub cover and total vegetation cover to decrease, while grass and bare cover increased with decreasing proximity to the water source. I found areal (g/m2) and percent (go SOC to be highest in the first 200m of the transects when accounting for the contribution of the three vegetation cover types. I concluded that SOC is being redistributed toward the water source via foraging and defecation and foraging, due to a negative trend of both total vegetation cover and percent SOC (g/g). With the decreasing trends of vegetation cover and SOC further from pasture water sources, my thesis research contributes to the understanding of storage and distribution of SOC stocks in arid rangelands. / Dissertation/Thesis / Masters Thesis Biology 2018

The primary objective of this research was to develop a landscape-oriented, process-based approach that can enhance understanding and prediction of SOC fluxes in IMLs by incorporating the key mechanisms impacting soil carbon dynamics when moving from the soilscape to the landscape. The mechanisms that are considered to be the focus of this study are redistribution of SOC due to erosion and deposition without neglecting the importance of litter incorporation into the soil column, decomposition due to microbial activity, and physical and chemical stabilization of carbon. To accomplish this objective, field experiments were performed to examine how selective entrainment of different soil size fractions, quantified through the enrichment ratio (ER), varies with management and hillslope position. Differential modes in soil mobilization between rill and interrill areas were either elevated or dampened depending on the prevalent management practice, the gradient of the site and landscape position. Sites where sediment and runoff fluxes were highest were found to have lower ER values (around unity) due to the mobilization of all size classes making static and dynamic samples almost identical. The size fractions analyzed in these experiments were found to have varying levels of carbon associated with them, especially the larger aggregates, which encapsulate organic material. Neglecting them in transport estimates could lead to large errors in predicted fluxes of SOC. For this reason, a careful attention was placed on identifying how aggregate stability varies with respect to management and hillslope position, through controlled experiments looking size distributions to reflect tillage disturbance and aggregate stability to assess resistance to rainsplash. Lastly, a landscape-oriented modeling framework was developed that captures not only the SOC spatial heterogeneity in IMLs but also determines the impacts that redistribution has on this heterogeneity and ultimately on SOC dynamics. The integrative modeling framework considers the collective effects of both rainsplash/rainfall- and tillage-induced erosion on SOC redistribution in IMLs through an ER-module developed and woven within this framework to connect an upland erosion model with a soil biogeochemical model. It provides not only size fraction updates to the active layer and ER values, but also explicitly considers the effects of splash-driven interrill erosion on those ER estimates. The model was applied to twentieth-century changes in SOC across a representative agricultural hillslope in the study watershed and compared to recent SOC data. The chronosequence in SOC storage within the erosional zone revealed that soils were continually depleted of the rich organic matter long after the 1930’s “Dust bowl” due to enhanced erosion that accompanied agricultural practices. However, conservation tillage and enhanced crop production that began in the late 1980’s reversed the downward trend in SOC losses, causing nearly 26% of the lost SOC to be regained. Results from this study can be used to aid policy and decision makers in developing a food-system that accounts for the co-evolution of human and natural activity, to develop sustainable agro-ecosystems through the use of data supported recommended best management practices.

The evaluation of the soil spatial variability using a fast, robust and cheap tool is one of the key steps towards the implementation of Precision Agriculture (PA) successfully. Soil organic carbon (OC), soil total nitrogen (TN) and soil moisture content (MC) are needed to be monitored for both agriculture and environmental applications. The literature has proven that visible and near infrared (vis-NIR) spectroscopy to be a quick, cheap and robust tool to acquire information about key soil properties simultaneously with relatively high accuracy. The on-line vis-NIR measurement accuracy depends largely on the quality of calibration models. In order to establish robust calibration models for OC, TN and MC valid for few selected European farms, several factors affecting model accuracy have been studied. Nonlinear calibration techniques, e.g. artificial neural network (ANN) combined with partial least squares regression (PLSR) has provided better calibration accuracy than the linear PLSR or principal component regression analysis (PCR) alone. It was also found that effects of sample concentration statistics, including the range or standard derivation and the number of samples used for model calibration are substantial, which should be taking into account carefully. Soil MC, texture and their interaction effects are other principle factors affecting the in situ and on-line vis-NIR measurement accuracy. This study confirmed that MC is the main negative effect, whereas soil clay content plays a positive role. The general calibration models developed for soil OC, TN and MC for farms in European were validated using a previously developed vis-NIR on-line measurement system equipped with a wider vis-NIR spectrophotometer (305 – 2200 nm) than the previous version. The validation results showed this wider range on-line vis-NIR system can acquire larger than 1500 data point per ha with a very good measurement accuracy for TN and OC and excellent accuracy for MC. The validation also showed that spiking few target field samples into the general calibration models is an effective and efficient approach for upgrading the implementation of the on-line vis-NIR sensor for measurement in new fields in the selected European farms.

Soil structure influences many chemical, biological and physical processes and it is well established that organic carbon acts as a soil binding agent. However, the precise location of organic matter and carbon in relation to structural features within intact samples is unknown. The sensitivity of organic carbon to decomposition is dependent not only upon its intrinsic chemical recalcitrance, but also its location within the soil structure. Soil structure provides organic carbon with chemical and physical protection, the extent of which varies between structural units. Furthermore soil structure is transient, and is sensitive to both environmental changes and physical disturbance, therefore it is difficult to determine and quantify the impact of this dynamic entity upon the storage of organic carbon. To date the majority of research that has advanced our understanding of the role soil structure plays in the storage of organic carbon, has relied upon some form of fractionation technique to separate aggregates from the bulk soil. However this approach has its disadvantages as much of the soil structure is destroyed; clearly when studying the impact of soil structure upon organic carbon-storage it is advantageous to implement any method that minimises disturbance to the soil structure. This study entails removing intact soil samples (through the use of kubiena tins) from long-term agricultural experimental fields at Rothamsted Research, (Hertfordshire, UK) with the aim of comparing and evaluating the location of organic matter and it’s associated organic carbon, in soils with contrasting organic carbon contents and a well documented land-use history. Thin sections will be analysed by integrating conventional micromorphology, image analysis and sub-microscopy combined with microscale chemical analysis scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). In doing so a new alternative method for analysing the distribution of organic matter and organic carbon is proposed. It was found that agricultural soils, which are the same in all aspects except total-OC content, differ in total organic matter, water release characteristics, aggregate stability and pore size distribution; therefore these differences could be attributed to the relationship between OC and soil structure. The water release curve, aggregate stability and pore size distribution also differed between soils with similar OC-contents but from different land-uses. The analysis of organic matter within intact soil samples provided evidence for the redistribution of organic matter as it is decomposed within the soil structure, for instance, less decomposed organ and tissue forms were located in or near to soil pores while more decomposed amorphous forms were located within the soil matrix. Since the same pattern of redistribution was observed in both agricultural and grassland soil this is likely to be directed by soil macro and micro fauna. It is concluded that since the location of different forms of organic matter is consistent across all soil, organic matter location is not responsible for creating differences in aggregate stability between treatments. Instead the results indicate that the amount and strength of organic carbon bonds and its hydrophobic properties are responsible. Micromorphology results demonstrated an absence of defined aggregation between treatments. Despite the difficulties in the interpretation of aggregation, the results contradict theories of aggregation, which state that aggregates are formed around “fresh” organic matter and it is argued that OM will undergo substantial decomposition before it acts as core for aggregation. Initial SEM-EDS analysis, has shown that in the soil matrix adjacent to organic matter (plant/organ) fragments there is a heightened concentration of C, indicating that these fragments are acting as a source of organic carbon. Interestingly BC, which represent one of the most recalcitrant C forms is also acting as a source of C, although these initial results suggest to a lesser extent than more labile C-sources. This source of organic carbon could stimulate microbial activity thereby enhancing soil structural stability. Alternatively, the release of liable carbon into soil pores may represent one route by which labile carbon enters sub-soil horizons.

Switchgrass (Panicum virgatum), a perennial C4 grass species, has the capacity to not only improve the quality of the soil in which it grows but also promote soil carbon storage to offset rising atmospheric CO2. This research investigated soil organic carbon (SOC) dynamics beneath switchgrass using natural abundance 13C and soil carbon fractionation following the establishment of this crop in a native and predominantly C3 plant region in southeastern Ontario. I investigated SOC dynamics by sampling adjacent commercial switchgrass fields and appropriate paired control fields at sites where the time since switchgrass establishment varied from 4-11 years. SOC and natural 13C abundance were measured in paired fields to assess management-induced changes in the quantity, source, and turnover time of soil carbon. To better elucidate carbon cycling dynamics over a relatively short time since switchgrass establishment, multiple soil fractionation techniques were applied to better understand carbon dynamics of soil organic matter with various mean residence times. Establishment of switchgrass results in marginal increases in SOC, primarily at sites where intensive soil management (i.e. tillage) practices preceded switchgrass establishment. Changes were observed in some of the more labile SOC pools, as well as in the δ13C values of the bulk soil and soil carbon fractions, indicating that growing switchgrass was causing the incorporation of switchgrass-derived carbon into the soil. Even resistant SOC pools, with turnover times of over 100 years, incorporated significant quantities of switchgrass carbon in 11 years. Annual increases in SOC, however, were less than values reported elsewhere. The potential for soil carbon storage exists, likely due to longer mean residence times of the carbon in soils beneath switchgrass compared with other cultivation systems. Changes in SOC following switchgrass establishment related strongly to the amount of root biomass, time since establishment and prior soil management practices. The decomposition rates derived in this research should be integrated into soil carbon modeling applications intended to support the emergence of switchgrass in southeastern Ontario. The results of my research can advance soil carbon models and be used to make regional assessment of the potential impact of growing switchgrass for bioenergy in southeastern Ontario. / Thesis (Master, Geography) -- Queen's University, 2012-01-30 13:56:06.269

High latitude soils are estimated to store a considerable part of the global pool of soil organic carbon (SOC). Studies of global and regional SOC pools have estimated total inventories in northern Sweden’s subarctic region to fall within 10-50 kg m-2. However, correction factors for stone and boulder content of soils are often overlooked in SOC-studies and soil profiles are commonly normalized to a depth of 1 m, which can result in substantial overestimates of the SOC pool if a large part of the soil volume is occupied by stones/boulders or if the soil depth is shallower than 1 m. This study was performed to quantify SOC in soils of the Torneträsk catchment area using detailed measures of soil depth and stone/boulder contents. Two non-destructive sampling methods, ground penetrating radar (GPR) and rod penetration, were used to measure soil depth and stone and boulder content in the catchment area. Results show that average soil depth (n = 52344) varied between 0.95 – 2.14 m depending on elevation and the average mire depth was 0.63 m. Stone and boulder content of the soil was estimated to 49 – 68 % depending on elevation. The results were added to existing carbon and soil density data from the Torneträsk catchment area and total SOC inventories were calculated to 6.8 – 13.1 kg m-2. The results of this study indicate that previous studies on regional and global scale may have overestimated the SOC pools in the subarctic regions of northern Sweden.

Overall soil productivity is declining in the U.S. due to loss of soil organic matter (SOM). Decreased SOM lowers soil water storage, reduces water infiltration, slows aggregate formation, and depletes soil of nutrients. In many systems, crop nutrients are replaced by expensive synthetic fertilizers that can lead to environmental concerns. This practice is not economically or environmentally sustainable in the long term. To secure future soil use and crop production, sustainable management practices are needed to prevent further SOM depletion. Incorporating legumes into cropping systems is one alternative that can bolster soil organic C (SOC) (key indicator of SOM) and reduce N fertilizer applications through symbiotic legume N fixation. Three studies were conducted over multiple years at the Texas A&M AgriLife Research and Extension Center near Overton, TX. Annual cool- and warm-season legumes were evaluated as potential green manure crops and intercrops under grain sorghum [Sorghum bicolor (L.) Moench], high-biomass sorghum [Sorghum bicolor (L.) Moench], and annual forage cropping systems. These studies quantified legume soil moisture usage and C and N contributions to the soil and subsequent crop yields in East Texas. Primary project objectives were to maintain or maximize primary crop yields at reduced N fertilizer rates and to build SOC through the integration of legume green manures and intercrops. Green manuring cool-season legumes showed the most beneficial effect on SOC, soil total N, and crop yields; however, significant increases in yield were only detected after three years in rotation. Intercropping Iron-and-Clay cowpea (Vigna unguiculata L. [Walp]) decreased yield of both high-biomass sorghum and grain sorghum due to competitive vegetative growth. Iron-and-Clay did however improve biomass yields of high-biomass sorghum in two subsequent years when implemented as a green manure. Despite large N yields as high as 310 kg ha-1, impacts of legumes on annual forage crops was limited. Poor response was likely a result of previous field history in which a permanent warm-season grass pasture was cultivated for site preparation and mineralized SOC released substantial amounts of available N. Under low soil N conditions, legume green manures produce enough N to likely reduce N fertilizer requirements cost-effectively for subsequent crops in East Texas.

The contribution of energy from biomass sources is projected to increase in Britain to assist in meeting renewable energy targets and reducing anthropogenic CO2 emissions. With increasing concerns over the sustainability of food crop-based biofuels, purpose-grown lignocellulosic biomass crops such as Miscanthus and short rotation coppice (SRC) willow have been promoted as more sustainable feedstocks for the production of heat and electricity as well as for the future production of liquid biofuels. With the introduction of the Energy Crops Scheme, land-use change (LUC) for lignocellulosic biomass crop production has become increasingly common in Britain in recent decades. However, there is limited understanding of the impact this has on soil organic carbon (SOC) stocks and limited predictability concerning the overall trajectory, magnitude and rate of SOC changes under a range of different conditions. Using a chronosequence of 93 biomass crop plantations in England and Wales, mainly of 1 to 14 years age, empirical models were developed to determine the short term trajectory of SOC stocks following LUC from arable and grassland to SRC willow and Miscanthus production. SOC stocks were calculated for each site using a fixed sampling depth of 30 cm and estimated changes were inferred by comparing with typical pre-change SOC stocks. These results indicate that only LUC from arable crops to SRC willow demonstrated an overall increase in SOC stocks, by an estimated 15.3 ± 2.2 t C ha-1 (± 95% confidence intervals) after 14 years and 68.8 ± 49.4 t C ha-1 after 22 years. LUC from arable crops to Miscanthus and from both arable crops and grassland to SRC willow and Miscanthus demonstrated no overall net effect on SOC stocks. Soil texture and climate data were measured for each site and multivariable models were created to assess the influence of different environmental conditions on SOC trajectory. In most cases the addition of these explanatory variables improved the model fit, and the models provide some preliminary estimates of more region-specific changes in SOC following LUC. Since LUC to biomass crops often causes a loss of SOC, at least in the short term, the potential for pyrogenic carbon (PyC) to ameliorate this effect was investigated. Studies indicate that PyC can interact with and stabilise native SOC, a process termed negative priming, although the potential for PyC to reduce LUC-induced losses of SOC by negative priming has not yet been assessed. Although negative priming has been observed in many studies, most of these are long term incubation experiments which do not account for the impact of environmental weathering of PyC on interactions with native SOC. Here the aim was to assess the impact of environmentally weathered PyC on native SOC mineralisation at different points in LUC from arable crops to SRC willow. Soil was sampled to a 5 cm depth from multiple recently established SRC willow plantations approximately 2 years after amendment with PyC. Cumulative CO2 flux was measured weekly from incubated soil and soil-surface CO2 flux was also measured in the field. The results demonstrate a PyC-induced increase in CO2 flux for the surface 5 cm of soil. However, no net effect on soil-surface CO2 flux was observed in the field. Although the mechanisms for these contrasting effects remain unclear, they do not suggest that PyC can reduce LUC-induced SOC losses through negative priming.

Made available in DSpace on 2014-06-11T19:30:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-05-28Bitstream added on 2014-06-13T20:40:16Z : No. of bitstreams: 1 rufino_amm_me_botfca.pdf: 2747239 bytes, checksum: cdbcc49d429a0f7df7aba9d1fac59f81 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O sequestro de carbono nos ambientes terrestres, sendo feito de forma natural pelos vegetais através da fotossíntese, cujo processo permite fixar o carbono nos solos e, em forma de matéria lenhosa nas plantas, vem sendo apontado como uma alternativa mitigadora das mudanças climáticas, segundo acordos internacionais como o Protocolo de Kyoto. A retirada da floresta nativa provoca a diminuição significativa da biomassa microbiana e da fertilidade do solo. A reserva de carbono na matéria orgânica do solo é uma importante estratégia para atenuar a concentração de CO2 na atmosfera. Com o reflorestamento dessas áreas ocorre uma recuperação lenta e contínua da quantidade e qualidade da matéria orgânica. O eucalipto é a essência florestal mais plantada no Brasil e essas plantações florestais com eucalipto poderão cumprir o papel de aumentar as concentrações de carbono orgânico no solo, recuperando estruturas perdidas quando da exportação da madeira através da colheita, bem como, provocando mudanças ambientais associadas. Este trabalho objetivou quantificar a fixação de carbono no compartimento do solo de 0 a 60 cm de uma floresta nativa em comparação com plantios de eucalipto com 3 diferentes idades: 0 a 1 ano (área recém implantada); 3 a 4 anos (metade do ciclo) e 6 a 7 anos (época de corte). Foram escolhidos quatro diferentes sítios de amostragem com uma área amostral de 1 ha cada. Foram coletadas amostras de solo no inverno e no verão a diferentes profundidades para que se pudesse conhecer a quantidade de carbono orgânico fixado ao longo do perfil do solo considerando o fator da sazonalidade. Os resultados indicam que o manejo nas áreas interferiu no acúmulo de carbono no solo dos quatro sítios estudados, mostrando também que o fragmento de Cerrado estoca menos carbono que os plantios de eucalipto. Quanto à sazonalidade, houve diferença significativa... / The carbon sequestration in terrestrial environments, by plants through photosynthesis, allows carbon fixing as a woody matter in plants. This process has been identified as an alternative to mitigate climate change, according to Kyoto Protocol, an international environmental agreement. The removal of the native forest causes a significant decrease of microbial biomass and soil fertility. The storage of carbon in soil organic matter is an important strategy to reduce the concentration of CO2 in the atmosphere. With the reforestation of these areas, occurs a slow and continuous recovery of the quantity and quality of organic matter. The eucalyptus is the most planted species in Brazil for industrial supply. These eucalyptus reforestations may fulfill the role of increasing soil organic carbon concentration, recovering some structures lost by wood harvesting and causing associated environmental changes. This study aimed to quantify the carbon fixation within the soil compartment from 0 to 60 cm depth of a native forest formation in comparison with eucalyptus plantations with 3 different ages: 0 to 1 year (newly planted area); 3 to 4 years (half the harvesting cycle) and 6 to 7 years (harvesting time). Four different sites were chosen for sampling, with a sampling area of 1 ha each. Soil samples were collected in winter and summer time, at different depths, to quantify the organic carbon fixed throughout the soil profile, considering the seasonality factor. The results indicate that management in each area interfered in the accumulation of carbon in the soil in the four sites studied. The savanna fragment stored less carbon than the eucalyptus plantations. Regarding seasonality, a significant difference was found between the accumulation of carbon in winter and summer... (Complete abstract click electronic access below)