Browsing by Author "Acosta-Martinez, Veronica"
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Item Arthropod and soil microbial communities in forage-livestock systems(2018-08) Bhandari, Krishna B.; West, Charles P.; Longing, Scott; Slaughter, Lindsey C.; Villalobos, Carlos; Acosta-Martinez, VeronicaThe rapid decline in water supply for irrigation in the Texas High Plains is encouraging some growers to convert their irrigated cropland to dryland forages for livestock production. The vitality of the Ogallala Aquifer, a source for water supply for irrigation in the semi-arid Texas High Plains, is severely threatened owing to withdrawal rates that far exceed recharge rates. ‘WW-B.Dahl’ Old World bluestem [OWB, Bothriochloa bladhii (Retz) S.T. Blake] is a drought-tolerant grass in dryland and limited-irrigation conditions. Adoption of low water requiring perennial forages such as WW-B.Dahl OWB in forage-livestock production systems could potentially extend the economic life of irrigated row crops. This grass is reported to deter some insects such as red imported fire ant (RIFA, Solenopsis invicta Buren); but its effect on broader arthropod taxa and on soil microbial communities is unknown. Fewer horn flies (Haematobia irritans L.) have been casually observed on cattle (Bos taurus L.) grazing this grass compared to other grasses; however, observations were non-tested testimonials, and definitive data are unavailable. Visual ratings (1-5 scale) were compared for horn fly densities on cattle grazing two forage systems: grass-only (predominantly OWB) vs. grass-legume (OWB and alfalfa). Arthropod and soil microbial communities occurring in OWB, OWB-alfalfa (Medicago sativa L.), alfalfa, native mixed grass, and teff (Eragrostis tef (Zucc.) Trotter) pastures were characterized over 3 yr. I compared soil chemical and microbial properties in a Pullman clay-loam soil among OWB, OWB-alfalfa (Medicago sativa L.), alfalfa and native mixed-grass pastures at 0‒5 cm and 10‒15 cm depths in June and December of 2016. Qualitative analysis of chemical composition of essential oils of OWB was performed by gas chromatography (GC) and GC-mass spectrometry (MS) methods. I make the following major conclusions: • There was not a clear deterrence effect of WW-B.Dahl OWB on horn flies on cattle when compared to cattle grazing a grass-legume pasture system, which entailed spending less time on OWB. There is still a need for insecticidal treatment to control horn flies grazing OWB. • WW-B.Dahl OWB provides an unfavorable habitat for colonization by RIFA and harvester ants. Pastures containing OWB are expected to deter cattle health threats and grass stand decimation owing to absence of RIFA and harvester ants, respectively. • OWB appears to exhibit minor inhibitory effects on bees and other insect pollinators when compared to native mixed grasses and alfalfa pastures; however, pollinator populations are likely not threatened. • OWB did not clearly suppress the canopy-dwelling arthropods, while still hosting some arthropods of ecological significance; it appears that there is low risk of reducing overall arthropod diversity by wide adoption of OWB in the Texas High Plains. • The consistently greatest number of soil microbial communities and favorable soil biological properties in the OWB-alfalfa pastures compared to other forage types indicated that OWB had no suppressing effect on soil microorganisms, thus OWB-alfalfa is a promising pasture combination. • The consistently highest concentration of a single essential oil compound, Spiro [4.5] dec-6-en-8-one, 1,7-dimethyl-4-(1-methylethyl)-, out of 143 detected, prompts the need for further study of this compound to test its biological activity against RIFA and harvester ants. Much lower abundance was naphthalene, a known insect deterrent; however, its role as an insect deterrent in OWB is unknown without further study. In summary, results of these studies add to a growing body of work supporting the value of WW-B.Dahl OWB as a well-adapted perennial forage grass in the Southern Great Plains thanks to ant deterrence while maintaining overall insect diversity and hosting desirable soil microorganisms.Item Bed Design as a Management Tool Affecting Soil Microbial Dynamics, Community Structure, and Soil Sustainability in a Dryland Cotton Production System(2020-02-26) Ghanem, Kholoud Zaki; Zak, John; Acosta-Martinez, Veronica; McMichael, Bobbie; Payton, Paxton; Jeter, RandallSoil temperature in dry-land cotton production systems can influence soil microflora activity and nutrient availability, and plant production. Field maintenance practices and soil temperature needs at planting could result in altered microbial dynamics as the season progresses. For conventional tilled cotton system on the Southern High Plains pitched beds are used to reduce erosion and increase temperatures at planting. However, as bed design could influence soil temperature dynamics, this study was designed to investigate the impacts of bed design on DTRsoil dynamics, microbial responses, and nutrient dynamics, determine the impacts of bed design on cotton growth, crop development and yield and evaluate seasonal microbial responses to DTRsoil conditions. The two bed designs that were evaluated are: 1: traditional pitched beds with 40 in centers and 2: flat beds with no-till. For each treatment six, 4 meter plots with five rows per plot were established in 2014 at the TTU farm in Lubbock, TX. These plots were sampled in 2014, 2015, 2016 and 2017. Soil samples to 15 cm depth were collected starting in May and followed monthly through November for each year. Microbial biomass carbon, enzymatic activities, FAME, and carbon usage by bacteria and fungi along with nutrient dynamics and soil moisture were evaluated. Bed design did impact soil temperature dynamics and moisture status, especially during the hottest and driest portions of the growing season. Pitched beds were warmer than flat beds at both depths, and experienced a higher DTRsoil through the growing season. Subsequently, the flat beds had the greater emergence and subsequent yields compared with pitched beds. The lower levels of microbial biomass with reduced DTRsoil could reflect higher turn-over of the biomass or that microbial biomass carbon is insensitive a metric for evaluating bed designs. Moreover, Flat-bed design had a beneficial impact on microbial community composition due to the higher fungi abundance in comparison with the Pitched beds across the growing season. Bed design is one management tool that could be employed in cotton production systems across the SHP to ameliorate soil temperature variability and the high DTRsoil that occurs in the region. The Flat bed (no-till) performed best under dry climates and limited precipitation, with yields often being equal to or higher than Pitched bed (tillage) practices, suggesting that it may become an important climate-change adaptation strategy for dryland region.Item Carbon sequestration and soil health in conservation reserve program grasslands in the southern high plains(2017-05) Li, Chenhui; Moore-Kucera, Jennifer; Weindorf, David C.; Acosta-Martinez, Veronica; Fultz, Lisa; Horita, JuskeInitiated in 1985, the Conservation Reserve Program (CRP) is one of the largest private-land conservation programs in the USA. The aim of CRP is to encourage landowners to convert highly erodible cropland or other environmentally sensitive acreage to vegetative covers, such as perennial grasslands, to improve environmental health. Numerous ecological benefits have been achieved as a result of the CRP program including soil erosion control, improvements in water quality, increased wildlife habitat, and carbon (C) sequestration. Soil microorganisms are involved in the majority of soil functions, such as nutrient provisioning and cycling, pest and pathogen protection, symbiotic and compensatory associations with plants, as well as the formation of stable aggregates to reduce soil erosion and build soil organic matter. Texas, and specifically the Southern High Plains region (SHP), leads the nation in acres enrolled in the CRP program. The three objectives of my research were: 1) to estimate a regionally specific C sequestration rate of the SHP region; 2) investigate the role of soil microbial processes that are important in C sequestration; and 3) to examine the influences of the long-term CRP grassland on soil biological/microbial health indicators in the SHP. A CRP chronosequence study (0-28 y as of 2014) was designed to address these objectives. Soil samples (0-10 cm and 10-30 cm) were collected in 2012 and 2014 from 26 fields across seven counties within the SHP and included seven croplands (representing 0 y in CRP), 16 CRP fields of varying ages (6-28 y), plus three rangelands sampled selected to serve as the reference system assumed that had never been plowed or cropped. The soils were dominated by either Amarillo or Patricia series, which are fine sandy loams and are highly susceptible to wind erosion. Relative to cropland, CRP grasslands with year-round plant cover provided supplementary plant organic residues into the soil and reduced soil diurnal temperature range, which supported greater microbial biomass and assisted C sequestration. Soil organic C (SOC) increased at a rate of 69.8 and 132.9 kg C ha-1 y-1 at depths of 0-10 cm and 0-30 cm, respectively. Scaling these results to the 0.92 million ha of CRP lands in the SHP resulted in an average C sequestration potential of 64.1 and 122 Gg C y-1 and would take approximately 74 and 77 y to reach the rangeland levels at depths of 0-10 cm and 0-30 cm, respectively. These results highlight the need for longer restoration periods and enhanced management efforts such as the proper integration of livestock into CRP lands to facilitate SOC accrual rates and associated ecosystem benefits, especially in the SHP region with extreme weather (e.g. frequent drought) and fragile, sandy soils. Soil microbial community size and metabolic activities increased and soil microbial community structure shifted in a direction of decreased bacterial abundance and increased fungal abundance particularly arbuscular mycorrhizal fungi (AMF) with the increasing CRP restoration years. The AMF provide numerous soil functions such as assisting plants in absorbing water and nutrients, especially phosphorus, increasing C sequestration, alleviating salinity, improving soil structure, sequestering potential toxic elements in soil, and biocontrol of plant pathogen. Rangelands that have not been disturbed by agricultural management practices and the old CRP fields were proposed to have highest AMF, but my data did not support this hypothesis. My results indicated that CRP restoration has a significant C sequestration potential and a great capability to recover soil health. However, there are still improvements that could be done if the management practices target enhancements of soil microbial community health, such as increased native grasses in the seeding mix or increased diversity with the addition of properly managed livestock to stimulate microbial processing important for ecosystem services within CRP land.Item Crop residue and no-till as management tools to enhance soil microbial community dynamics in a dryland cotton system in the southern High Plains(2021-12) Vargas Gutierrez, Diana Lucia; Zak, John; Acosta-Martinez, Veronica; Jeter, Randall; Stevens, Richard; Wakeman, KatherineAgricultural production systems across the Southern High Plains face significant challenges due to increasing climate variability interacting with conventional practices that can decrease soil health. Therefore, there is an urgent need for improvement of soil health for cotton production systems by implementing conservation agriculture management practices, such as crop residue and no-till, that will increase the activities of soil microbial communities and mitigate the environmental impacts resulting in a more sustainable agriculture across the region. The purpose of this research was to assess the effects of conservation management practices, such as crop residue management combined with no-till practices, to enhance the soil microbial community dynamics and crop production in a dryland monoculture cotton production system in the Southern High Plains. The research was carried out over four growing seasons (2014 to 2017). For the 2014–2015 growing seasons, 2 treatments were established: 1) using erosion blankets to mimic stubble (shade), and 2) sorghum or wheat residue (stubble) and control (no stubble) with 6 replicate plots in each treatment and control. For the 2016–2017 growing seasons, the shade treatment was not included. Soil samples were collected before planting and over the growing season (monthly) to evaluate environmental and nutrient parameters, microbial community size and structure, function, diversity and composition. Over the four years the addition of stubble reduced daily soil temperature range (DTRsoil) by approximately 6 °C on average at the soil surface and approximately 3 °C at 15-cm below the surface during the hottest months. Soil moisture was increased by 33 % and 49 % in the last two years when compared to the control. The combined effects of reduced DTRsoil and increased soil moisture had a positive effect on microbial activities. Overall, microbial biomass carbon increased across all growing seasons except in 2015 under stubble. Total bacterial FAME levels were higher in all growing seasons under stubble except in 2016. Total fungal FAME levels were higher in all growing seasons under stubble. Both fungal and bacterial FAME levels were influenced by changes in daily temperature variability with stubble application. NH4+-N and NO3--N levels decreased in the stubble in 2014 and 2016, and SOM increased substantially in 2014 and 2017 in the stubble. Overall, all enzyme activities increased under stubble, except β-glucosidase in 2016. Bacteria functional diversity using BIOLOG increased over time, with the greater differences in 2016 and 2017 when compared to the control. Both enzyme activity and bacterial functional diversity were correlated. Fungal functional diversity decreased over time except for a substantial increase in 2016 and was correlated with β-glucosaminidase and arylsulfatase activities. Fungal community composition as assessed by whole-community DNA sequencing was dominated by Ascomycota and Basidiomycota phyla, with the highest relative abundance of Basidiomycota under the stubble. The main fungal genera observed in the dryland systems were Fusarium, Phoma and Alternaria. The implementation of conservation management practices, such as crop residue and no-till, mitigated the climate variability with the reduction in daily soil temperature variability and increase of soil moisture, which positively affected the dynamics of microbial communities and their functions. Although the benefit from no-till and stubble management was not observed every year, the gradual improvement of microbial community dynamics will increase soil health, thus leading to a productive and sustainable agriculture in the long term.Item Determination of the effects of carbon nanotubes on plants, soil microorganisms and phytoremediation of arsenic and polycyclic aromatic hydrocarbons(2012-12) Shrestha, Babina; Anderson, Todd A.; Cox, Stephen B.; Payton, Paxton R.; Acosta-Martinez, VeronicaTremendous growth in nanotechnology research has been observed in recent years because of its potential application in diverse fields. Because of the unique physicochemical, mechanical, and electrical properties, carbon nanotubes (CNTs) are the most widely used nanomaterials. There are two main types of CNTs: single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). Ecotoxicology studies on nanomaterials and CNTs have increased in recent years, however, there is still very limited literature available on the environmental impact of manufactured nanomaterials. Understanding the ecotoxicological effects of nanomaterials and CNTs is deemed necessary to prevent the possible risk to humans and organisms. The Environmental Protection Agency has been emphasizing the need for research leading to the application of nanomaterials for environmental protection as well as the assessment of risk associated with nanomaterial applications. The objective of this dissertation study was to determine the effects of MWNTs on plants, soil microorganisms, and phytoremediation of arsenic and polycyclic aromatic hydrocarbons (PAHs) in soil. It was observed during the study that MWNTs at concentrations up to 1000 mg/ kg have no effects on soil metabolic functioning and microbial community composition. However, pyrosequencing demonstrated a shift in soil microbial community structure to more tolerant genera like Rhodococcus, Cellulomonas and Nocardioides (Actinobacteria) and Pseudomonas (Gammaproteobacteria) in the presence of extremely high MWNT concentrations (10000 mg/kg). There were no negative effects of MWNTs on seedling growth and germination of corn, cotton, alfalfa and sorghum. Uptake of MWNTs in roots of 8 d old corn and cotton seedlings was low (< 20 mg MWNT/kg dry biomass) in most MWNT treatments except MWNT accumulation was high (between 20 - 40 mg/kg) at the highest treatment (10000 mg/kg) in both corn and cotton. Similarly, uptake in 40 d old corn was also low (< 20 mg MWNT/kg dry biomass) comparable to 8 d old seedlings. However, translocation to above ground parts was very limited for both 8 d old (corn and cotton) and 40 d old corn, and MWNTs were detected in only a few samples. There were no negative effects of MWNTs on plant photosynthetic response in corn, however maximum photosysnthesis rate and light saturated photosysnthesis were slightly stimulated in in the presence of the two highest concentrations of MWNTs. There were also no negative effects of MWNTs on photosysnthetic pigment content and total percent nitrogen in corn leaves. Similarly, MWNTs did not show oxidative stress on corn roots. The results from these studies suggest that there are no negative effects of MWNTs on soil microorganisms, germination and seedling growth and, physiological and biochemical responses in later stages of plant growth. However, plants can uptake CNTs. Hence, there is possibility of transfer of CNTs to higher organisms through food chain transfer. Also, the presence of extremely high concentration of MWNTs (10000 mg/kg) in a worst case scenario might cause changes in soil microbial community composition. A study conducted on the influence of MWNTs on PAH rhizodegration found pyrene mineralization in a sandy clay loam soil significantly increased by 21 % in the highest MWNT treatment group (100 mg/kg). Microbial community composition was not influenced by the MWNT treatments in this sandy clay loam soil (3.4 % organic carbon content). However, microbial community structure in both the control and MWNT treatments showed a dramatic shift in the presence of MWNTs in the sandy loam soil (0.5 % organic carbon content). Many microbial FAMEs (i15:0, 16:1ω5c, 10 Me 17:0, 10Me 16:0) were missing in the control soil and these FAMEs showed a lower abundance in the 25 mg/kg MWNT treatment (except 10Me 17:0) while the presence of these FAMEs was higher in the 50 mg/kg and 100 mg/kg MWNT treatments. This study was able to show that MWNTs can influence the different factors of PAH rhizodegradation which will depend on different soil types with different organic carbon content in soil. The results from the 28 d study on arsenic hyperaccumulation in Chinese brake fern (Pteris vittata) showed that arsenic hyperaccumulation decreased in the presence of MWNTs and functionalized MWNTs (FMWNTs) in soil after both 21 and 28 d of exposure. However, the decrease was only statistically significant in MWNT treated soil at 28 d. The study indicates that MWNTs and FMWNTs might sequester arsenic in soil making it less bioavailable for uptake and bioaccumulation in plants. These studies have provided useful data on the effects of MWNTs on contaminant bioavailability which will be useful in the evaluation of nanomaterials as well as possible applications in various remediation processes. Although nanomaterials are considered beneficial for use in various sectors, this study indicates the need for regulation of their application to minimize the future risk to humans and the ecosystemItem Effects of daily soil temperature range on microbial community dynamics in a dryland cotton production system in West Texas(2015-08) Vargas-Gutierrez, Diana Lucia; Zak, John; Jeter, Randall M.; Acosta-Martinez, VeronicaGlobal mean temperature has increased in the last decade from 0.10 to 0.16 ºC, leading to a decrease in the daily temperature range (DTR= Tmax-Tmin) where the night time minimum temperature (Tmin) is increasing at a faster rate. Changes in daily Tmin and Tmax can have a positive or negative consequence to agriculture production depending upon crop type and location, but little is known about the possible effects of DTRsoil on microbial community dynamics. The main goal of this study was to evaluate the impacts of daily temperature range (DTRsoil) on the microbial community size, structure and functional diversity in a dryland cotton production system on the South High Plains. Six plots were established during the 2013 growing season using wood-fiber erosion control blankets to reduce DTRsoil. Six control plots were established adjacent to the reduced DTRsoil plots. Soil samples were collected before planting and over the growing season, from planting beds and from the furrows between the beds, from each set of plots and analyzed to evaluate microbial biomass carbon, microbial community composition, enzymatic activities, and carbon usage by bacteria and fungi. DTRsoil was reduced by 11ºC at the soil surface and by 4°C at 15 cm under the erosion blankets in comparison with the controls plots across the growing season. The reduction in DTRsoil led to an increase in microbial biomass C as the crop developed as compared to control plots, as well as an increase in of Gram (-) bacteria, arbuscular mycorrhizal fungi, saprophytic fungi and protozoan FAME markers. Levels of extractable NO3--N, NH4+-N and P were higher under control plots in comparison with reduced DTRsoil plots indicating the reduction in DTRsoil regulated nutrient dynamics and increased nutrient uptake into microbial biomass. Microbial functional capabilities as evaluated by-glucosidase, -glucosaminidase, arylsulfatase, alkaline phosphatase and phosphodiesterase and BIOLOG functional diversity were higher within the reduced DTRsoil plots as the crop developed as compared to control plots. Fungal functional diversity, substrate activity and substrate richness did not show a response to either a reduction in soil DTR or if samples were taken from planting beds or furrows. Cotton stand development was poor in the control plots and was significantly higher in the reduced DTRsoil plots. The cotton in the reduced DTRsoil plots went on to produce a yield comparable to dryland cultivation under a good year. The reduction in DTRsoil positively affected the dynamics of microbial communities and relationship with plants, which can lead to good crop development.Item Long term responses of microbial biodiversity to changes in precipitation in a Chihuahuan desert grassland: Implications towards understanding effects of global climate change(2009-12) Bell, Colin; Zak, John; Acosta-Martinez, Veronica; Cox, Stephen; McIntyre, Nancy; Sirotnak, JoeGlobal climate models predict increased temperature and precipitation variability in arid regions throughout southwestern North America within the next century, resulting in fewer rain events of greater magnitude, and longer periods between rain events. Longer inter-pulse periods coupled with increased air temperature will greatly reduce soil moisture availability. Although many studies have addressed the short-term impacts of precipitation variability on soil microbial and biogeochemical response patterns in arid ecosystems, few efforts have directly assessed the role of precipitation-pulse shifts in regulating long-term functional- or structural soil-microbial community responses over more than a couple of years. This research examined soil microbial and edaphic responses to climate model predictions of 25% increased seasonal rainfall applications over a 7-year period between 2002-2008 to determine long-term soil microbial responses to climate change with respect to variable rainfall in a Chihuahuan Desert sotol grassland at Big Bend National Park. We hypothesized that over time, these minor but realistic increases in moisture would produce a measurable accumulative change in microbial, biogeochemical, and edaphic properties. To characterize the soil microbes in this desert grassland, community structure was classified as bacterial (gram-negative, gram-positive, and actinomycetes) and fungal (saprophytic fungi and arbuscular mycorrhiza) categories using fatty acid methyl ester (FAME) techniques. Microbial community functional responses to precipitation were characterized via carbon substrate utilization and enzymic activity. Our results strongly suggested that seasonal soil moisture timing and magnitudes regulate soil microbial ecosystem functionality. These results further suggested that minor shifts in the magnitude if rainfall patters are capable of altering soil microbial community dynamics in this desert grassland at Big Bend National Park. Over time, increases in moisture (25% additions based on climate change predictions) produced cumulative changes in soil microbial, biogeochemical, and edaphic properties. Microbial community structural and functional responses emerged during the fourth year of this study, as the relative abundances of saprophytic fungi, AM fungi, and gram negative bacteria, and soil exoenzymes β-Glucosidase (responsible for cellulose degradation) and Phosphodiesterase (responsible for phosphorus mineralization) displayed elevated levels in the summer + winter (SW) watering plots during this period. Interestingly, once the microbial response occurred in 2005, the changes in microbial community structure and function remained throughout the duration of the study (2006-2008) irrespective of annual ambient rainfall amounts received over the succeeding three years. This change in the microbial structure and function suggests that different components of the soil-microbial community may provide similar ecosystem function, but differ in response to seasonal temperature and precipitation. As soil microbes encounter altered precipitation amounts and timing along with increased soil temperatures predicted for this region, the ability of the soil microbial community to maintain functional resilience across the year may be reduced in this Chihuahuan Desert ecosystem.Item Microbial Responses Under Differing Ecosystems to Promote Agricultural Sustainability on the Texas Southern High Plains(2023-08) Petermann, Billi Jean; Slaughter, Lindsey C.; Lewis, Katie; Laza, Haydee; Acosta-Martinez, Veronica; Steffan, JoshuaAgricultural producers in semi-arid regions face many challenges while attempting to increase soil health and profitability, particularly climatic extremes that contribute to severe water and nutrient scarcity. Historically, cotton production in the Texas Southern High Plains has relied heavily on continuous tillage, monocropping, and supplemental irrigation to produce a profitable yield under challenging climatic conditions, such as variable precipitation, extreme temperatures, and prolonged drought. However, as groundwater resources continue to decline, producers are adopting conservation management practices, such as no-tillage, cover crops, and crop rotations, to improve soil health and water storage. Soil microbial community size and composition drive many functions that influence plant productivity, such as nutrient cycling, improved soil structure, and subsequent water dynamics, making them important indicators that can be used to assess soil health improvements. Our study aimed to compare soil physical, chemical, and microbial responses in two bulk soil depths (0-10 cm, 10-20 cm) and root zone soil from cotton production systems in semi-arid, coarse-textured soils managed with three different long-term (> 7 years) management strategies, each under high and low irrigation levels at two locations with different soil textures. Cropping practices included a typical agroecosystem (Continuous mono-crop with conventional tillage, CCCT) compared to two conservation systems that included a no-tillage with small grain cover crop (NTCR) and a no-tillage with a cotton/wheat rotation (NTCW) for two years. In the fine sandy loam textured soil, results revealed management-induced differences in soil microbial communities and other soil health indicators regardless of irrigation level. The conservation systems had greater total FAME markers as indicators of soil microbial community size and soil organic matter than the CCCT system. Furthermore, the NTCW maintained greater AMF abundance than the conventional practices. In addition, higher enzyme activities involved in C, N, and P cycling were detected under conservation systems. In addition, the bacterial and fungal microbiomes had similar compositions at the phylum level under all management systems. However, the community structure of the microbiome was influenced more by management practices than irrigation levels at lower taxonomic levels. Drought-tolerant taxa dominated bacterial communities, with no significant differences between high and low irrigation. Environmental conditions at the Lamesa site influenced the composition of the bacterial and fungal microbiomes, with management practices affecting the community structure. Overall, this study suggests that no-tillage and diversified planting strategies can improve biological soil health indicators in these semi-arid sandy loam soils regardless of irrigation level. At the Halfway site, classified as having a clay loam texture, results revealed management and irrigation-induced differences in microbial abundance and structure but had a limited effect on enzymatic activity. The conservation management systems had greater SOM, total FAME, and select biomarker abundance than the CCCT, especially under drought conditions. In addition, high irrigation levels supported a greater microbial abundance. The microbiome results revealed higher bacterial and fungal richness in the conservation treatments depending on the sampling zone and year. At the phylum level, we found that the bacterial and fungal community composition was similar across all management and irrigation treatments. However, conservation practices at this site consistently influenced the bacterial and fungal microbial structure at the ASV level with communities that differed from the CCCT regardless of irrigation in all sampling zones across the three years of the study. Strong correlations between the total water applied via rainfall and irrigation and the relative abundances of the dominating bacterial phyla revealed increases in drought-tolerant taxa regardless of management and were more responsive to overall water conditions than the fungal community. Overall, the results support that conservation management practices improved soil health in semi-arid clay loam soil and may promote a more resilient soil environment during drought at this site. Furthermore, the microbiome at this site was influenced by management practices and overall water conditions (rainfall + irrigation), suggesting that even under supplemental irrigation, the soil microbiome is more responsive to annual climatic variability in this region and can be further altered with conservation management practices in this semi-arid clay loam.Item Microbial, enzymatic, and soil nutrient dynamics associated with debris dam revegetation efforts of low degraded tobosa grasslands in the Chihuahuan Desert at Big Bend National Park(2011-08) Ortiz, Apolinar; Zak, John; Acosta-Martinez, Veronica; Jeter, Randall M.With the increase of temperature and the amount of land lost to desertification, scientists must learn to monitor, control, and reestablish the land for future generations. This study,conducted innorth part of Big Bend National Park, Chihuahuan Desert examined the ability of the debris dam approach to reestablish critical soil microbial activity and community structure in conjunction with revegetation efforts of low elevation arid grasslands. Debris dams previously established by resource managers at Big Bend National Park in 2006 were sampled in January, May, August and October 2010 and January 2011 along with bare soil and an ajacent intact tabosa grassland. For all locations, a 7cm diameter by 15cm long bucket auger was used to take soil samples at 15cm increments to a depth of 45cm total (3 increments per core). At each sample date microbial biomass carbon and FAME analyses were conducted to ascertain microbial community structure. Functional characteristics of the soil bacteria and fungi were evaluated using BIOLOG and FUNGILOG procedures and key microbial enzymes (Phosphodiesterase, β-Glucosidase, and Phenol oxidase). Soil nutrient and edaphic properties were also obtained for each sample date. The debris dam approach did reestablish important microbial activity in these degraded low desert grasslands. Microbial biomass carbon levels had increased substantially as compared with the bare soils and were even higher than the natural grassland possible. Microbial community structure was similar between the natural vegetation and the debris dams after 4 years. Although fungi dominated all three locations, Gram Negative bacteria and Actinomycetes dominated the bare soil while Gram Positive Bacteria dominated the natural vegetation and debris dam soils. Soil nutrient dynamics were similar between the debris dams and natural vegetation areas as important microbial and plant linkages were reestablished. Importantly, the high levels of extractable NO3-N that characterize the bare soils in this region of Big Bend National Park with the loss of vegetation were reduced under the debris dams as nitrogen becomes immobilized in the vegetation and with greater microbial biomass. All microbial enzyme activities were higher under the natural vegetation with the debris dams intermediate in activity levels between the natural vegetation and the bare soil. Microbial carbon use was also similar in that microbial functional capabilities were intermediate between the natural vegetation and the bare soil. The microbial and nutrient data indicates that debris dams can be effective in restoring plant cover to formally bare regions in the Chihuahuan Desert without the need for supplemental water. Once plants are reestablished, regardless of species, important microbial dynamics and associated ecosystem processes are increased above levels that had been occurring in the bare or disturbed soils. Moreover the trajectory of the microbial and soil nutrients suggests that these vegetated bands are sustainable as critical aspects of nutrient mineralization coupled with increased microbial activity have been promoted. In addition from a practical standpoint, the debris dams will be more effective than the intensive investment of planting drought tolerant plants that can become evasive and threatening to the naturally occurring plants within Big Bend National Park.Item Modeling landscape-scale water balance in irrigated cotton systems(2013-08) Booker, Jon D.; Zartman, Richard E.; Lascano, Robert J.; Evett, Steven R.; Acosta-Martinez, Veronica; Mulligan, KevinCotton production is an important component of the culture, economy, and landscape in the Southern Ogallala Aquifer region and is reliant on irrigation using water pumped from the non-rechargeable aquifer. It is estimated that ~ 60% of the irrigation in the area uses center pivot equipment. As water from the aquifer becomes an increasingly limited and regulated resource, cotton producers, consultants, and researchers could benefit from using simulation models that account for spatial and temporal variability in irrigation, inter-seasonal weather, and soil pedology. In order to provide decision support information that can interact with current variable rate equipment abilities, such models must be effective at the production scale (> 50 ha) and at a spatial and temporal resolutions relevant to management decisions (e.g., 20-m grid and 1-h time steps). The Precision Agricultural-Landscape Modeling System was specifically developed to meet these scale and resolution requirements, but lacked a specific cotton model. It was hypothesized that integrating the cotton growth model Cotton2K with PALMS to produce PALMScot would provide an approach towards modeling pivot irrigated cotton systems at a landscape-scale. Our experimental objectives were i) to integrate the Cotton2K and PALMS models to form PALMScot; ii) evaluate the use of the model and its capability to calculate soil water content and plant growth in two contrasting soil series, across two growing seasons, and two levels of irrigation; iii) evaluate the model’s capability to calculate soil water content and plant growth at multiple locations within a production-scale, pivot irrigated cotton field across two growing seasons with divergent weather conditions; and iv) evaluate the model’s capability to calculate soil water content, plant growth, and boll and lint production at multiple locations across a ~ 56-ha production field characterized by variability in soil pedology. Results showed that PALMScot provides a continuous accounting of mass and energy balances, and integrates interactions between the atmosphere, soil, and above and below ground physiological plant processes. Deviations of model-calculated from measured soil water content values were consistently < 0.02 m3 m 3, measures of calculation efficiency were positive in most cases, and deviation between calculated and measured plant heights were consistently < 0.10 m in both Amarillo fine sandy loam and Pullman clay loam soil series. Therefore, we conclude that PALMScot correctly calculates soil water content and crop growth across the unique scale of a production field and could provide decision support input at the fine spatial and temporal resolution required for precision agriculture and management of pivot irrigated cotton systems at a landscape-scaleItem Multi-location study of soil enzyme activities as affected by types and rates of manure application and tillage practices(2011) Acosta-Martinez, Veronica; Mikha, Maysoon M.; Sistani, Karamat R.; Stahlman, Phillip W.; Benjamin, Joseph G.; Vigil, Merle F.; Erickson, Richie (TTU)Significant amounts of manure are produced in the USA; however, informationon the changes in ecosystem services related to soil biogeochemical cycling foragroecosystems supported with organic amendments such as manure is limited. Amulti-location field study was initiated in Colorado (CO), Kansas (KS) and Kentucky (KY),USA in loam soils to evaluate the effects of manure and tillage practices on enzymeactivities that are key to biogeochemical cycling such as β-glucosidase (C cycling),α-galactosidase (C cycling), β-glucosaminidase (C and N cycling) and phosphomonoesterases(P cycling). The treatments were as follows: (i) two years of beef manure applications to afine sandy loam at different rates (control: 0, low: 34 kg N ha−1 and high: 96 kg N ha−1)and tillage practices in CO; (ii) three years of beef manure applications to a silt loam atdifferent rates (0, low: 67 kg N ha−1 and high: 134 kg N ha−1) and tillage practices in KSand; (iii) three years of poultry and dairy manure applications to a silt loam with differenttillage practices at the same rate (403 kg N ha−1) in KY. Tillage practices (none vs. conventional) had no effect on the enzyme activities. Principal Component Analyses (PCA)grouped all enzyme activities with the high beef manure application rate after the first yearin CO at 0–5 cm. By the second year, the low and high beef manure rates differed inenzyme activities for the KS soil with no difference between the low rate and control in CO. Since the first year of the KY study, acid phosphatase activity was greater in the poultrytreated soil compared to dairy or the control; whereas, C cycling enzyme activities weresimilar in soil treated with dairy or poultry manure. For all studies, PCAs for soil samplesfrom 5–10 cm depth did not reveal treatment separation until the second year, i.e., onlyhigh application rate differed from the other treatments. Results of the study indicatedsignificant responses in C and P cycling enzyme activities to manure applications withintwo years, suggesting potential benefits to soil biogeochemical cycling essential for theproductivity of agroecosystems supported with organic fertilizers.Item Production and soil effects of sorghum biofuel cropping systems in semiarid marginal regions(2012-05) Cotton, Jon; Moore-Kucera, Jennifer; Acosta-Martinez, Veronica; Burow, Gloria B.; Wester, David B.In order to meet the growing demands for food, fiber, and biofuels, land management decisions will require identification of lands most suitable for each crop. Biofuel production that occurs on lands otherwise constrained for other intensive agricultural production by soil or water limitations (i.e., marginal lands) may not only meet some of these demands but, if managed properly, may also help improve soil function. For large-scale application to be sustainable, identification of crop type most efficient for feedstock production as well as impacts on soil and water resources are necessary. In this study, forage sorghum (Sorghum bicolor L. Moench) cropping systems were initiated in the semiarid Southern High Plains (SHP) of the U.S. to evaluate potential biofuel production and potential benefits on soils that are depleted of organic matter (< 0.7%) due to previous cropping history. Systems consisted of two sorghum cultivars (Sorghum Partners 1990 = SP 1990 and PaceSetter bmr = PS bmr) differing in lignin content due to brown midrib trait (bmr-12) that were tested under two different water levels (non-irrigated or deficit irrigation of 2.88 mm day-1), and biomass removal rate treatments of 50% and 100%. Forage sorghum SP1990 (non bmr) produced significantly higher weight and volumes of biomass than PS bmr under both deficit irrigation and no irrigation in the two years of study. However, PS bmr biomass was converted into ethanol (EtOH) 54% more efficiently during both years. When below average precipitation occurred during the first year of the study, both cultivars produced similar amounts of EtOH at each irrigation level (1,600 to 3,380 L ha-1). When higher than average precipitation occurred during the second year, higher biomass production of SP 1990 resulted in more EtOH production than PS bmr (3,380 vs. 2,640 L ha-1). Irrigation resulted in 26-49% more biomass and 28-72% more EtOH production during both growing seasons, indicating that non-irrigated production resulted in deficit water conditions regardless of precipitation. Overall EtOH production ranged from 1,600 to 3,380 L ha-1 during both years of the study. Changes in soil microbial properties (0-10 cm), known to be sensitive econsensors, were measured during the two year transition from previous long-term cotton cropping systems to the sorghum biofuel cropping systems. Increases in microbial biomass C (MBC) and N (MBN) (16-17%) and differences in fatty acid methyl ester (FAME) profiles were observed after one growing season. Additionally, soil enzyme activities (EAs) targeting C, N, P, and S increased 15-75% after two growing seasons. Increases in EAs 16-19%) and differences in FAME profiles were seen due to the irrigation treatment, which may be due to the increase in belowground biomass production even under deficit irrigation. When biomass was not fully removed (50% removal treatment), increases in MBC and MBN (11-15%), b-glucosidase (C cycling) and alkaline phosphatase (P cycling) (12-22%) occurred, which is likely attributed to the protection of the soil surface from aeolian erosion provided by the surface residue. The cultivars tested, which produced biomass with different chemical composition, had little effect on the soil microbial properties measured during the time frame of this study. This study indicates that chemical modifications and biomass yield potential are critical factors when selecting sorghum characteristics for use as biofuel feedstocks under marginal water-deficit conditions. These cropping systems also have the potential to improve sandy, low organic matter soils in this semiarid region, as was shown by increases in microbial biomass and soil functionality indicated by EAs after only two growing seasons. Early results from this study suggest sorghum biofuel cropping systems can be a sustainable practice for marginal lands in the SHP; however, tracking of long-term changes are necessary to fully evaluate effects. It is hypothesized that soil properties will continue to improve, especially in the lower biomass removal level as more above-ground biomass will be incorporated and decomposed. It is unclear how the chemical composition of biomass from different sorghum cultivars will impact soil properties but differences in organic matter accumulation and enhanced biochemical cycling are possible. Finally, additional research on incorporating biofuel production into traditional cotton production, along with the evaluation of novel sorghum cultivars specifically bred for use as feedstock, are important focuses for the application of biofuel production in the semiarid SHP.Item Soil Health Assessment and Management Framework for Water-Limited Environments: Examples from the Great Plains of the USA(2023) Ghimire, Rajan; Thapa, Vesh R.; Acosta-Martinez, Veronica; Schipanski, Meagan; Slaughter, Lindsey C. (TTU); Fonte, Steven J.; Shukla, Manoj K.; Bista, Prakriti; Angadi, Sangamesh V.; Mikha, Maysoon M.; Adebayo, Olufemi; Noble Strohm, TessHealthy soils provide the foundation for sustainable agriculture. However, soil health degradation has been a significant challenge for agricultural sustainability and environmental quality in water-limited environments, such as arid and semi-arid regions. Soils in these regions is often characterized by low soil organic matter (SOM), poor fertility, and low overall productivity, thus limiting the ability to build SOM. Soil health assessment frameworks developed for more productive, humid, temperate environments typically emphasize building SOM as a key to soil health and have identified the best management practices that are often difficult to implement in regions with water limitations. This study reviewed existing soil health assessment frameworks to assess their potential relevance for water-limited environments and highlights the need to develop a framework that links soil health with key ecosystem functions in dry climates. It also discusses management strategies for improving soil health, including tillage and residue management, organic amendments, and cropping system diversification and intensification. The assessment of indicators sensitive to water management practices could provide valuable information in designing soil health assessment frameworks for arid and semi-arid regions. The responses of soil health indicators are generally greater when multiple complementary soil health management practices are integrated, leading to the resilience and sustainability of agriculture in water-limited environments.Item Soil Health Assessment in Double Cropping Wheat Systems Across Texas(2023-12) Valencia, Hector L.; Lewis, Katie L.; Acosta-Martinez, Veronica; Foster, Jamie L.; Slaughter, LindseyConservation practices such as no-tillage and double-cropping are less common in the Southern Great Plains, especially Texas, compared to other regions of the United States. These practices have the greatest potential to reduce wind erosion and improve soil health in the typical sandy soils found in this region. However, research is needed to identify double cropping systems suited to the area and determine their effect on soil health. The overall objective of these series of experiments was to evaluate the effects of conservation management practices on various agroecosystems across Texas (Beeville, Lubbock, and Thrall) by measuring soil properties that are indicative of soil health. Specifically, we wanted to determine the effects of double cropping systems, under multiple tillage regimes, on select soil biological indicators across Texas. Secondly, we wanted to evaluate a novel assay in the simultaneous determination of enzymes compared to the sums of individually assayed enzymes, while also evaluating its use as a biogeochemical nutrient cycling index. Implementation of a secondary crop in a continuous wheat production system combined with reduced or no tillage, generally increased soil health indicators when compared to conventionally tilled fallow systems. Nutrient cycling potential of carbon, nitrogen, phosphorus, and sulfur was generally greater at 0-5 and 5-15 cm in cropping systems that implemented a secondary crop. Reduced tillage practices (no-till and strip-till) generally had greater activity at 0-5 cm with greater activity in conventionally tilled plots at 5-15 cm. Potassium permanganate oxidizable carbon was generally greater in plots that incorporated a cover crop mix at 0-5 cm with greater levels determined in conventionally tilled plots at 5-15 cm. Soil organic carbon measurements were not as sensitive to cropping systems and tillage treatments at 0-5 and 5-15 cm across all locations, with limited significance determined between treatments. The simultaneous determination of β-glucosidase, β-glucosaminidase, acid phosphatase, and arylsulfatase exhibited a significant positive linear relationship with the sum of individual enzyme activities measured in Beeville (R2 = 0.65), Lubbock (R2 = 0.85), and Thrall (R2 = 0.96). Overall, simultaneous determination of enzyme activity was greatest in systems that implemented a secondary crop at 0-5 and 5-15 cm when compared back to the fallow system. Conservation tillage management practices (no-till and strip-till) measured greater enzyme activity when compared to conventional tillage at 0-5 cm, but the opposite was measured at 5-15 cm with greater enzyme activity measured in conventionally tilled systems. This is likely attributed to residue retention at soil surface with conservation tillage practices and inversion of organic residues deeper into soil profile with conventional tillage. This study suggests that implementation of a secondary crop, through double cropping, and reduced tillage, such as strip-till and no-till, have the potential to be used as a viable management strategy across Texas in terms of increasing the soil health of a system. Limitations of the length of the study was unable to determine significant differences or trends in soil organic carbon and the need to conduct long-term double cropping studies is still needed to evaluate the complex dynamics associated with management and soil organic matter.Item Soil Health Assessment to Evaluate Conservation Practices in SemiArid Cotton Systems at Producer Site Scale(2023) Acosta-Martinez, Veronica; Cotton, Jon; Slaughter, Lindsey C. (TTU); Ghimire, Rajan; Roper, WayneMaintaining soil health and sustainable crop production has been challenged by climate variability and wind erosion in semi-arid regions. To understand the initial effects of the transition of tilled cotton systems to no-tillage with winter wheat as a cover crop, we sampled 18 commercial grower sites from 2019 to 2022 in the Southern High Plains (SHP). We evaluated the soil biological component, which often responds rapidly to changes in residue additions or minimized soil disturbance providing an early indication of changes in soil health, especially in the low organic matter soils in this region. After two years, compared to tilled systems, no-till systems had significant increases in ester-linked fatty acid methyl ester (EL-FAME) bacterial and saprophytic and AMF fungal markers, enzyme activities of nutrient cycling, and various SOM pools, under both center-pivot irrigation and dryland. Similar increases were also observed in two dryland sites sampled before and up to two years after transition to no-till. Our study demonstrates the potential of no-tillage and cover crops to improve soil health in cotton production in semiarid regions, and a framework for a soil health assessment that links different soil health indicators with functions related to soil organic matter, soil water, and biogeochemical cycling.Item Soil health management in cotton monocultures on the Texas High Plains(2018-05) Burke, Joseph Alan; Lewis, Katie; Acosta-Martinez, Veronica; McLendon, Terry; Moore-Kucera, Jennifer; Ritchie, Glen L.; Williams, Ryan B.The Texas High Plains (THP) is a semi-arid ecoregion with soils susceptible to wind erosion. Soil conservation management practices like reduced tillage, residue management, and cover cropping have been shown to reduce wind erosion potential. In other regions of the United States, conservation management practices such as no-tillage and cover cropping have been shown to provide additional benefits to cash crops and improve soil health but have not been thoroughly evaluated on the THP. Adoption of these conservation management practices have been limited in this region due to limited knowledge in adoptable practices and concerns regarding water-use and potential limitations, like nutrient immobilization and pest pressure. The overall objective of these series of experiments was to identify potentially adoptable practices for improved soil health management under the typical practice of cotton monocultures on the Texas High Plains. For example, the effects of no-tillage and cover cropping on soil C dynamics, nutrient availability, microbial respiration, soil aggregation, stored soil moisture, cotton yield, cropping system economics and sustainability were assessed. With field studies, soil organic C (SOC) increased 57% using conservation tillage and a mixed species cover compared to conventional tillage in sandy soils of this region. Additionally, SOC and potassium permanganate oxidizable C (POXC) were greatest during periods of active cotton and cover crop root growth. Soil organic C and POXC were significantly correlated (R2=0.75), but SOC and POXC were poorly correlated to microbial respiration (R2=0.3 and 0.12, respectively). Conservation management practices did not appear to have an impact on inorganic N fractions or soil aggregation. Stored soil moisture was reduced with cover crops but was greater than the conventional system following termination prior to planting the cotton (Gossypium hirsutum L.) cash crop. Deeper in the profile, stored soil moisture replenishment was greatest following cover crops. Decreased cotton lint yields in the no-tillage with rye cover treatment resulted in reduced lint revenue, gross margins, and sustainability compared to the conventional system; however, there were no significant differences between the conventional and no-till mixed species cover systems. Conservation management practices such as, no-tillage and cover crops increased SOC and POXC especially during winter fallow periods, improve infiltration and decrease evaporative potential, and helped improve several sustainability indicators including water-use efficiency and quality, soil conservation, and energy use. These conservation management practices demonstrated the potential to improve several ecosystem services, like nutrient cycling, under cotton monoculture production systems on the THP. Our results suggest further research is necessary to better understand yield differences under long-term conservative management scenarios.Item Soil health variability among residential landscapes impacts urban water conservation(2019-12) Sapkota, Manish; Young, Joseph Ronald; Coldren, Cade; Slaughter, Lindsey; Acosta-Martinez, VeronicaSoil health or quality have been used synonymously to describe soil physical, chemical, and biological parameters. Soil quality/health is expected to improve over time, but few studies have determined those parameters from residential lawns in semiarid climates. The objectives were to 1) Determine physiochemical and microbiological attributes of urban soils established under turfgrass landscapes of different ages, and 2) Evaluate the importance of turfgrass management in structuring soil physiochemical properties and microbial communities. Soil samples were obtained from front lawns of residential homes within the following categories in 2018 (n=10) and 2019 (n=9): oldest (pre-1970), middle (1971-1990), newer (1991-2010), and newest (2011-present). Soil texture, bulk density, extractable nutrients, pH, soil organic matter (SOM), soil organic carbon (SOC) and total nitrogen (TN) were determined from soil collected in 2018. Soil microbial biomass and composition were determined for soil obtained in 2018 and 2019. Bulk density and pH were highest in newest homes and lowest in oldest homes, but no differences in CEC, K, Mg, or Ca were identified. Increasing home age increased SOM, SOC, TN, and microbial biomass regardless of management practices as determined by homeowner surveys and variation of visual quality of turfgrass within home age categories. Neither total FAMEs nor fungal composition differed for home age categories, but bacterial biomass increased with home age. Pairwise comparisons between home age categories using multi-response permutation procedures (MRPP) in Non-metric multidimensional scaling (NMS) ordination showed significant differences for 28 biomarkers except for middle and oldest home age categories. Management practices like irrigation, fertilization, and pesticides showed negligible influence on soil microbial composition based on non-parametric tests whereas no effect was observed for microbial biomass. The primary factor that affected accumulation of SOM, SOC, TN, and microbial biomass within landscapes was age of the residential home. Increased SOM and SOC in middle and oldest home age categories demonstrate reduced fertility and irrigation requirements to the lawns.Item Soil microbial community diversity and functionality as affected by integrated cropping-livestock systems in the Southern High Plains(2012-12) Davinic, Marko; Moore-Kucera, Jennifer; Acosta-Martinez, Veronica; Zartman, Richard E.; Zak, John; Dowd, Scot E.Soil microorganisms constitute a small proportion of soil but are vital to the overall functioning and stability of ecosystems. The soil biota is frequently regarded as the “biological engine of the earth” as it performs many fundamental processes including nutrient cycling, soil structural dynamics and stability, degradation of pollutants, and regulation of plant communities. Introduction of molecular techniques has increased our analytic proficiency by providing greater taxonomic resolution and depth of coverage for microbial community assessments. Despite these advancements, one of the fundamental challenges in microbial ecology is to determine the relationship between community composition and function. Agricultural sustainability in the semi-arid Southern High Plains, U.S. is challenged by soils of inherently low fertility, depleting water resouces and highly variable and extreme weather conditions. Alternative agricultural management for the Southern High Plains region involves integrated livestock-crop production systems (ICL) which have shown to reduce water usage, fuel costs associated with irrigation, and potential to improve multiple soil quality parameters compared to monoculture crop production. The first objective of this research project focused on assessing microbial community structure and functionality under ICL compared to the typical practice of continuous cotton. The second objective was to evaluate the spatial distribution of the microbial community and the relationship of these microbial assemblages on the chemical composition of organic and mineral components. The first chapter contains background information on microbial diversity, community structure and their imporatance on ecosystem functionality as well as an overview of the major methods used to assess microbial structure and function. The second chapter combined physical, chemical, and molecular techniques to assess relationships between soil bacterial community structures and the quantity and quality of soil organic carbon (SOC) at the soil microenvironment scale (e.g., within different aggregate size-fractions). To accomplish this goal, soil samples from ICL and cotton systems were separated into macroaggregates (>250 μm), microaggregates (53-250 μm), and silt+clay (<53 μm) fractions and were analyzed for (1) bacterial diversity via pyrosequencing of the 16S rRNA gene and (2) SOC quantity and quality using a combustion method and mid-infrared diffuse reflectance spectroscopy (mid-IR), respectively. The mid-IR data revealed distinct spectral features indicating that these fractions were also distinguished by organic and mineral composition. Results from pyrosequencing showed that each soil microenvironment supported a distinct bacterial community, and that distributions of the less abundant bacterial phyla were more important for differentiating between communities in soil microenvironments. In the third chapter, mycorrhizal and saprophytic fungal populations (via fatty acid methyl ester profiles; FAME) and saprophytic fungal functionality (via FungiLog analysis) were evaluated under two ICL agroecosystems and a continuous cotton system at 0-5 and 5-20 cm depths. In addition to systems level comparisons, the effects of the vegetative components and grazing on fungal dynamics were evaluated. Abundance of saprophytic fungal FAMEs (10 to 26% of total FAMEs) and mycorrhizal FAMEs (2 to 24% of total FAMEs) were higher under ICLs compared to the continuous-cotton system at 0-5 cm. Overall, vegetation impacted the distribution of the fungal FAME markers, whereas the fungal saprophytic functionality was more sensitive to grazing. Perennial vegetation of ICLs was associated with increased fungal markers (saprophytic and mycorrhizal) as well as increased soil OM content. Higher fungal functional diversity was found under cotton, non-grazed perennial vegetation (with exception of bermudagrass) and the rotation under millet. Among the grazed perennial vegetation, bermudagrass showed the highest fungal FAMEs abundance and functional diversity values. These fungal improvements were also reflected in the highest OM content under this grass, potentially indicating improved sustainability under the OWB and bermudagrass agroecosystem. The fourth chapter describes results from microbial diversity according to pyrosequencing and enzymatic assays used to assess the effect of ICL systems and continuous cotton on bacterial and fungal diversity and (enzymatic) activity in these systems. Our data indicated that the microbial communities were distinct among the systems and vegetation, and the continuous cropping, whereas bacterial diversity indices, in general, were not impacted, reduced that fungal diversity. Lignin and cellulose degrading saprophytic fungi were prevalent under cotton containing systems, while perennial grasses were characterized by increased abundance of mycorrhizal fungi, implying that these two fungal groups play major roles in soil processes under these systems. Vegetation that had positive relationship with mycorrhizal and saprophytic fungal groups resulted in the highest enzymatic activity. This study also found positive correlation between certain bacterial and fungal taxa and soil properties such as total carbon, microbial biomass carbon and enzymatic activities. Investigation of microbial dynamics among agroecosystems at multiple spatial scales and taxonomic resolutions, provided insights to linking microbial community and functionality, and determining the overall impacts of agricultural management on the stability and resilience of these ecosystems.Item Soil microbial community response to management in improved pastures of the semi-arid Texas Southern High Plains(2019-05) Otuya, Rael Khayeli; Slaughter, Lindsey C.; West, Charles P.; Deb, Sanjit K.; Acosta-Martinez, VeronicaThe Southern High Plains (SHP) of the USA agriculture (crop and livestock production) is faced with many challenges such as limited water for irrigation, due to declining water levels of the Ogallala Aquifer. The insufficient and irregular rainfall, coupled with strong gusting winds that increase evapotranspiration worsens the situation. In addition, the soils in this region are highly degraded with < 1% soil organic matter (SOM). There’s a need for producers to adopt novel pasture-livestock management practices that are water efficient and that promote soil health and environmental sustainability such as the use of compost manure, use of legumes and limited irrigation coupled with grazing. Multiple research experiments were conducted in this thesis research to assess how alternative nutrient sources such as composted manure addition and legume forages (alfalfa and yellow sweetclover) interseeded with the WW-B. Dahl [WW-B. Dahl; Bothriochloa bladhii (Retz.), S.T. Blake perennial pasture impact soil biota and soil health in the SHP. In addition, we evaluated forage utilization practices: grazing contrasted with haying effect on soil’s biological, chemical and physical properties. Three pastures systems with different ages, past, and present management systems were evaluated. Key research conclusions include: Compost amendment increased total microbial biomass and changed the soil ecology as indicated by Non-metric multidimensional scaling (NMS) plots showing differences in microbial communities in compost and no compost treatments based on the selected phospholipids fatty acid (PLFA) biomarkers in fall 2018. Compost amendment increased soil total C, N, and SOM concentrations. Use of cattle manure could, therefore, be a sustainable and cost-effective way to enhance soil microbial communities, soil health and potentially increase forage yield in the SHP. The grass-legume mixture pasture system with long grazing history with no synthetic fertilization had higher total phospholipid fatty acid (PLFA), higher total C, N, SOM concentrations, and forage yield when contrasted with young grass-legume mixtures and pure stand grass pasture systems. The grass-legume mixture pasture system with long grazing history with no synthetic fertilization was ecologically different from young grass-legume mixtures and pure stand grass pasture. An interaction between year and grazing revealed that grazed treatment plots had a higher total carbon concentration indicating that grazing enhances soil organic carbon concentration. The grass-legume pasture had a higher N concentration than grass only suggesting that legume might have helped in N fixation. Overall, all the novel pasture management practices above, compost amendment, legume inclusion, and grazing are promising in enhancing soil microbial communities, promoting soil health and improving forage yield to sustain the economically important livestock industry in the SHP.Item The impacts of simulated nitrogen deposition on soil microbial communities along the Pine Canyon Watershed at Big Bend National Park, TX(2011-08) Grizzle, Heath W; Zak, John; Acosta-Martinez, Veronica; Cox, Stephen B.; McIntyre, Nancy E.; Strauss, Richard E.Anthropogenic nitrogen deposition in arid ecosystems is relatively low when compared to mesic systems. However, because arid ecosystems are characterized by low precipitation and high potential evapotranspiration rates in addition to nutrient limitations additional anthropogenic N deposition will likely have major effects on community structure and function of soil microorganisms relative to the effects found in mesic systems. Determining the impacts of N deposition in arid systems is critical as they cover more than 40% of the global land surface, contain a large portion of agricultural lands and are inhabited by more than 1 billion humans. This study evaluated how a simulated increase in annual N deposition and variable precipitation affected soil microbial functional diversity in a mid-elevation Sotol grassland and high-elevation Oak-Pine forest in the Chihuahuan Desert in Big Bend National Park, TX. Microbial functional diversity functional diversity parameters and monthly precipitation were measured and evaluated at both sites biannually from August 2003 to August 2006 and seasonally in the Sotol grassland in 2007. Differences in bacterial and fungal functional diversity on carbon substrates and fungal functional diversity on nitrogen substrates were estimated via Biolog microtiter plates from 2003 to 2007. Additionally, FAME analysis was used to evaluate relative proportions of soil bacteria and fungal groups during 2007. Finally, extracellular enzymes were evaluated during 2007 to evaluate the contribution of microbial enzyme activity on carbon, nitrogen and phosphorus cycling. Fungal functional diversity on carbon substrates was increased by low level nitrogen treatments in the Oak-Pine forest. However, increased nitrogen deposition did not effect carbon utilization in the Sotol grasslands. Fungal utilization of amino acids was significantly altered by increased nitrogen deposition in the Sotol grasslands. Additionally, Gram-negative bacterial community abundance and nitrogen cycling enzymes showed a seasonal response to additional nitrogen deposition in the Sotol grasslands. Seasonal influences and variable precipitation had a strong effect on most of the measured microbial community structural and functional parameters in the Sotol grasslands throughout the project. The difference in responses between the sites is largely due to differences in soil temperature, precipitation patterns and the different plant communities associated with each site.