This study worked with tomato plants, one soil and one peat moss, and three different composts, addressing the effects of composts and their combinations with soil and peat moss on tomato growth and soil fertility, and reduction of phytotoxicity of immature compost caused by high NH4 content. Different composts affected tomato growth differently due to nutrient differences existing among the composts. The higher the nutrients content the better the growth. Using peat moss greatly promoted tomato growth through fertilization and increased nutrient accumulations in plant leaves and soil nutrient residual availability, but this effect was limited to compost containing high content of nutrients. Under normal fertilization practice, each of the various plant growth indices showed highly correlated relationship with total plant dry weight, thus some of the growth indices, such as numbers of plant leaf and flower, could be used to predict tomato production without undertaking destructive harvest. Also each of the major plant nutrients accumulated in plant leaves showed a highly correlated relationship with total plant dry weight. The maturity of compost was an important factor in assessing the effects of composts on tomato growth and soil fertility. Plants growing in the mature compost medium benefitted from fertilization with nitrate, using NO 3 nutrient greatly increased plant growth and nutrient accumulations in plant leaves and also increased soil K residual availability. Plants growing in the immature compost medium benefit from fertilization with K, using K nutrient tremendously increased plant growth and nutrient accumulations in plant leaves. Immature compost was improved in their capacities to increase plant growth if additional K fertilization was provided. Fertilization with adequate dosage of K was a very effective method to reduce phytotoxicity caused by high content of NH4 in immature compost. The proper dosage set by this research was 0.6 g K/kg media. The effects on accumulation of nutrients in plants and nutrient residual availability in media were complex and were related to factors such as total plant growth and interactions of nutrients with one another with respect to availability for absorption by plants.

abstract: Modern agriculture faces multiple challenges: it must produce more food for a growing global population, adopt more efficient and sustainable management strategies, and adapt to climate change. One potential component of a sustainable management strategy is the application of biochar to agricultural soils. Biochar is the carbon-rich product of biomass pyrolysis, which contains large proportions of aromatic compounds that influence its stability in soil. Concomitant with carbon sequestration, biochar has the potential to increase soil fertility through increasing soil pH, moisture and nutrient retention. Changes in the soil physical and chemical properties can result in shifts in the soil microbiome, which are the proximate drivers of soil processes. This dissertation aims to determine the compositional and functional changes in the soil microbial community in response to the addition of a low-volatile matter biochar. First, the impact of biochar on the bacterial community was investigated in two important agricultural soils (Oxisol and Mollisol) with contrasting fertility under two different cropping systems (conventional sweet corn and zero-tillage napiergrass) one month and one year after the initial addition. This study revealed that the effects of biochar on the bacterial community were most pronounced in the Oxisol under napiergrass cultivation, however soil type was the strongest determinant of the bacterial community. A follow-up study was conducted using shotgun metagenomics to probe the functional community of soil microcosms, which contained Oxisol soil under napiergrass two years after the initial addition of biochar. Biochar significantly increased total carbon in the soils but had little impact on other soil properties. Theses analyses showed that biochar-amended soil microcosms exhibited significant shifts in the functional community and key metabolic pathways related to carbon turnover and denitrification. Given the distinct alterations to the biochar-amended community, deoxyribose nucleic acid (DNA) stable isotope probing was used to target the active populations. These analyses revealed that biochar did not significantly shift the active community in soil microcosms. Overall, these results indicate that the impact of biochar on the active soil community is transient in nature. Yet, biochar may still be a promising strategy for long-term carbon sequestration in agricultural soils. / Dissertation/Thesis / Doctoral Dissertation Microbiology 2020

Mollisols (called Black soils) are of major agricultural importance in China. Most of these soils have been used agriculturally for the last 50 years or so. Due to intensive cultivation and improper soil management, loss of organic matter and yield suppression resulting from soil erosion are serious problems in the region. The current research studied the physical and chemical properties of a typical Mollisol in China, characterized the changes of soil organic carbon (SOC) with cultivation, investigated the effects of agricultural management systems on SOC and total organic nitrogen (TON) contents and their vertical distribution, and examined the negative impacts of continuous soybean on crop and soil productivity. The soil is characterized with a thick (60 cm) mollic epipedon, higher organic carbon (5.8%), CEC (43.7 cmol(+)/kg) and macro-aggregate (>0.25 mm) stability, and greater macronutrients and water availability in the upper epipedon. Bulk density increases with depth, and total porosity declines with depth. Soil texture is clay loam. Overall characteristics make this soil fertile and productive. The SOC content declined rapidly at early years of cultivation and gradually afterwards. Compared with organic matter in the uncultivated soil, total SOC loss was 17%, 28%, and 55% in 5-, 14- and 50-year cultivation, respectively. Wheat-soybean rotation with addition wheat straw or pig manure resulted in a substantial increase in SOC content in 9 years. Compared with a wheat-corn-soybean rotation, continuous cropping reduced SOC and N contents in the profile, particularly SOC content. Moldboard plowing significantly reduced SOC and N contents whereas integrated tillage increased SOC and N relative to conventional tillage. Use of chemical fertilizers (N, P, and K) along with return of crop residues resulted in a substantial increase in SOC and N in top layers of the soil. Continuous soybean results in unbalanced soil enzymes activities, declines of SOC, total K, Zn, available K and N contents, soil pH and bacteria/fungi ratio. It is proposed that the best management for maintaining soil productivity in the area would be crop rotation along with the integrated tillage and addition of crop residues and chemical fertilizers.

Soil organic matter (SOM) plays an essential role in agriculture and in environments. It influences the productivity and physical well-being of soils. Therefore, it is important from both an economic and environmental standpoint to determine how agricultural practices will affect SOM and the biological cycling of carbon. Based on the changes of SOM characteristics, we further investigated the sorption dynamics and mechanisms of organic compounds in soil and SOM fractions under different soil managements. Several experiments were conducted and the results and conclusions were summarized as below. Long-term tillage experiment was initiated in 1979 at the Clemson University Pee Dee Research and Education Center (Darlington, SC). Cover crop experiment was conducted in the Connecticut River Valley at the Massachusetts Agricultural Experiment Station in South Deerfield, Massachusetts (since 1990). Cross-Polarization Magic-Angle-Spinning (CPMAS) and Total Sideband Suppression (TOSS) solid-state 13C Nuclear Magnetic Resonance (NMR) and Diffuse Reflectance Fourier Transform Infrared (DRIFT) spectroscopic techniques were used to identify the structural and compositional changes of SOM. Metolachlor sorption experiments (3 days) were conducted using a batch-equilibrium method. Three desorption steps were carried out for a total of 9 days in a sequential decant-refill steps following the sorption experiment. Our NMR results indicated that humic acid (HA) from rye alone cover was more aromatic and less aliphatic in character than other cover crop systems without nitrogen fertilizers. Based on the DRIFT peak height O/R (reactive/recalcitrant) ratios, the highest ratio was found in the HA from vetch/rye system with nitrogen fertilizer. Compared to conventional tillage (CT), conservation tillage (CnT) held a higher SOM and light fraction (LF) in the surface layer (0–5 cm). Aromaticity of HA increased with soil depth in both tillages. Conversely, the aliphatic-C content decreased with soil depth. However, the aromaticity of HA in CT was higher than that of CnT in the top soil (0–5 cm). Sorption nonlinearity (N) of metolachlor and hysteresis were dependent on the structure and composition of SOM. These results showed that agricultural practices not only changed the structure of SOM, but also changed the pesticide sorption behavior in the soil.

The colloidal behavior of engineered nanomaterials exposed in an aquatic environment may significantly influence their bioavailability as well as toxicity to different species. Natural organic matter (NOM) is one of the major colloidal materials ubiquitous in the environment with significant structural heterogeneity. Therefore, role of NOM molecules on environmental fate of these engineered NPs needs to be addressed. Colloidal behavior of aluminum (Al2O 3) and magnetic iron oxide (γFe2O3) NPs was studied in the presence of structurally different HAs and synthetic polyacrylic acids (PAAs). The conformation behavior of the adsorobed NOM/polyelectrolyte under specific solution conditions were determined with dynamic light scattering, atomic force microscopy measurements. Al2O3 NPs followed the classical DLVO model of colloidal behavior in their pristine state. However, a significant deviation from the classical DLVO model was observed when these NPs were coated with structurally different HAs. Low polar, high molecular weight HA fractions showed much stronger stabilization against Ca2+ induced aggregation. Previously, we observed that these low polar, high molecular weight fractions strongly destabilized the NP suspension when added in a small quantity. A significant transformation in suspension stability was observed possibly due to steric effect of these adsorbed HAs. The colloidal behavior of PAA/NOM coated ferrimagnetic γFe 2O3 NPs were investigated. Pure γFe2O 3 NPs were extremely unstable in aqueous solution but a significant enhancement in colloidal stability was observed after coating with polyelectrolytes/NOM. The steric as well as electrostatic stabilization introduced by the polyelectrolyte coating strongly dictated the colloidal stability. The alteration of electrosteric stabilization mechanisms by pH-induced conformation change profoundly influences the colloidal stability. Atomic force microscopy (AFM) study revealed a highly stretched conformation of the HA molecular chains adsorbed on γFe 2O3 NP surface with increasing pH from 5 to 9 which enhanced the colloidal stability trough long range electrosteric stabilization. The depletion of the polyelectrolytes during dilution of the suspension in the acidic solution conditions and in the presence of Na+ or Ca 2+ decreased the colloidal stability. The conformation of the polyelectrolytes adsorbed on the NP surface altered significantly as a function of substrate surface charge as viewed from the AFM imaging.

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Two groups of container experiments were conducted to study heavy metal absorption by plants. The objectives of the first group of experiments were: (1) to evaluate the effect of Cd, Pb, and Cu, on productivity, essential oil content and quality of peppermint, basil, dill, and sage, and (2) to estimate metal transfer and accumulation in plant parts and in the essential oils. In the first experiment, elevated concentrations of Cd (2, 6, and 10 mg/L), Cu (20, 60, and 150 mg/L), and Pb (50, 100, and 500 mg/L) on basil, peppermint, and sage were evaluated. Cadmium and Pb did not decrease peppermint yields. The application of Cu. at 60 and 150 mg/L reduced yields compared to the control. Basil yields were reduced by application of Cd at 6 and 10 mg/L, Ph at 500 mg/L, and Cu at 20, 60, and 150 mg/L. Sage yields were reduced by Cd at 6 and 10 mg/L, Pb at 50, 100, and 500 mg/L, and by Cu. at 60, and 150 mg/L. All three plants developed phytotoxicity symptoms in the 150 mg/L Cu treatment. In the next experiment, the following concentrations were applied to peppermint and basil growth medium (in mg/L): Cd 10; Pb 100; Cu 100; Cd 10 + Ph 100; Cd 10 + Cu 100; Ph 100 + Cu 100; Cd 10 + Ph 100 + Cu 100; and control (without metal addition). The following metal concentrations were applied to the growth medium of dill (in mg/L): Cd at 2, 6, and 10; Pb at 50, 100, and 500; Cu at 20, 60, and 150, and a control (without metal addition). Neither of the compost treatments resulted in toxic tissue concentration of heavy metals. Both compost and heavy metal applications induced alterations in the essential oil constituents of peppermint, dill, basil, and sage, without a clear trend. However, the essential oils from the four plants from all treatments were not polluted with Cd, Cu, and Pb. In conclusion, peppermint, dill, basil, and sage could be grown in metal polluted soils as cash crops or for phytoremediation, without risk of contamination of the end product, the essential oils. (Abstract shortened by UMI.)

Allelopathy, secondary metabolite–mediated plant-to-plant interaction, is gaining application in current agricultural science as well as in invasion ecology. The present study addresses the major knowledge gaps in this field by investigating (i) how the bioavailability of allelochemicals is altered when they are present in a mixture in the soil matrix and (ii) what are the cues and consequences of allelochemical production in nutrient acquisition by the plant. ^ The role of preferential sorption to soil in altering the chemical composition of plant exudates was studied in a silt loam soil using representative mixtures of plant phenolic acids, namely, hydroxybenzoic acid, vanillic acid, coumaric acid, and ferulic acid. The concentration-dependent sorption coefficient ( Kd) of hydroxybenzoic acid was decreased more by than 90% in the presence of coumaric acid. About 95% of sorbed vanillic acid was displaced into the soil solution in the presence of ferulic acid. Soil organic matter was associated with preferential sorption. The results demonstrate that preferential sorption of phenolic acids to soil can alter the availability of plant exudates in mixtures and thus may mediate their phytotoxic effects. ^ To understand the dynamics of allelochemical mixture in soil matrix, using Centaurea maculosa Lam.as a model source, we investigated how the bioavailability of complex allelochemical mixtures is modified in a soil-microbial system. C. maculosa litter decomposition experiment revealed the existence of allelochemical in complex mixture in soil matrix. We observed the prolonged persistence of allelochemicals in soil matrix when present in complex mixtures. Also, allelochemicals exhibited dynamic nature undergoing simultaneous degradation as well as synthesis. ^ We investigated allelopathy as a corollary effect of resource acquisition mechanism using Centaurea diffusa Lam. as a model system. The exudation of 8-hydroxyquinoline (8HQ) by C. diffusa was not correlated with any of the tested nutrient stresses; however the 8HQ production remained steady under prolonged Fe stress, indicating this as a specific plant response to Fe stress. 8HQ showed high specificity in extracting Fe from both invaded and non-invaded soils. C. diffusa was able to uptake Fe from Fe(OH)3, but addition of carbon resulted in Fe deficiency, indicating a direct role of 8HQ in Fe uptake by this plant. Related (C. maculosa, C. solistitialis) as well as non related species (Zea mays ) of C. diffusa were able to uptake Fe from Fe-hydroxyquinoline complex (FeQ). Combining the above with the root reductase activity of the species, we propose that FeQ because of its hydrophobic nature, could passively diffuse across plasma membrane. In bioassay studies the addition of Fe decreases the toxicity of 8HQ, suggesting the phytotoxic action of 8HQ is via chelation of cellular Fe. ^ In conclusion, the present study revealed the competitive sorption phenomenon of plant secondary metabolites in soil matrix, as well as their dynamic nature. Combining the results from these studies that, 8HQ not only mobilizes the nutrients from soil, but also these nutrient complexes can be taken up by plants, we report an additional role of 8HQ in increasing the competitive ability of this weed - by facilitating the resource acquisition. Also, we report for the first time, the possible existence of a phytosiderophore-like mechanism for Fe acquisition in non-graminaceous species. ^

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