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京都大学 / 新制・課程博士 / 博士(農学) / 甲第24655号 / 農博第2538号 / 新制||農||1097(附属図書館) / 学位論文||R5||N5436(農学部図書室) / 京都大学大学院農学研究科農学専攻 / (主査)教授 白岩 立彦, 教授 中﨑 鉄也, 教授 丸山 伸之 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

The purpose of this research carried out in 1998 and 1999 was to develop methods for strip cropping of cucumbers with rye/vetch and black plastic mulch. Effects of planting methods, weed control measures, and cover crop management techniques on pest and beneficial insects, petiole sap nitrate-nitrogen, soil moisture, yields and economic viability were assessed. Four treatments, namely cucumber direct seeded in black plastic mulch on tilled bare ground (conventional); cucumber direct seeded in black plastic mulch laid over incorporated rye/vetch residue; cucumber direct seeded into no-till rolled rye/vetch; and seedlings transplanted into no- till rolled rye/vetch, were evaluated in a randomized complete block design. Weeds were controlled in half the plot by critical manual weeding and pre-emergence herbicides applied in the other half in all treatments except the conventional system. Three-week interval staggered plantings of buckwheat to provide flowers for adult beneficial insects were also evaluated. Results obtained indicate that rye/vetch habitat is more attractive to beneficial insects than cucumber beetles before rolling or flail mowing. There were higher densities of adult Diptera (an indicator for Tachinid parasitoids) in both years and of Pennsylvania leatherwings in 1999 in plots with rye/vetch than in plots with rye only before planting. Preferential attraction to adult Diptera was not found after planting with no differences in cumulative densities between no-till and black plastic mulch plots after rolling or flail mowing. However, adult Diptera densities were positively correlated with cucumber yield, higher densities of cucumber beetles occurred in black plastic mulch than in no-till plots in both years, and bacterial wilt, transmitted by cucumber beetles, was reduced in no-till in 1999. Similarly, rye/vetch habitat plots had a higher diversity of Carabidae species (in both habitat areas and crop rows) before rolling or flail mowing, and higher densities of Carabidae (in habitat areas), Staphylinidae (in both habitat areas and crop rows) and spiders (in crop rows) after rolling or flail mowing. Black plastic mulch plots with flail mowed, incorporated rye/vetch residues had higher petiole sap nitrate-nitrogen and higher early season cucumber plant dry weights than in conventional plots; later in the season, the highest petiole sap nitrate-nitrogen occurred in no-till plots. No-till had higher marketable cucumber yield than plastic systems. The profitability of these production systems depended more on differences in marketable yield than on cost differences. The plastic with incorporated rye/vetch and no-till transplant systems were more profitable during early harvests in late July, while no- till direct seeded and transplant systems were more profitable from early August onwards. The three-week interval staggered planting of buckwheat led to conservation of beneficial insects, and the second and third seeded buckwheat flowering periods coincided with the period vetch had lost flowers. / Ph. D.

Conclusions: the absorption hygrometer cannot be used satisfactorily to measure differences in evaporation from small plots. / Master of Science

Increased floodplain and wetland restoration activity has raised concerns about potential impacts on the release of greenhouse gases (GHGs) to the atmosphere due to restored connectivity between aquatic and terrestrial ecosystems. Research has shown GHG fluxes from hydrologically active landscapes such as floodplains and wetlands vary spatially and temporally in response to primary controls including soil moisture, soil temperature, and available nutrients. In this study, we performed a semimonthly sampling campaign measuring GHG (CO2, CH4, and N2O) fluxes from six locations within a third-order stream floodplain. Site locations were based on dominant landscape positions and hydrologic activity along a topographic gradient including a constructed inset floodplain at the stream margin, the natural levee, an active slough, the general vegetated floodplain, a convergence zone fed by groundwater, and the upland area. Flux measurements were compared to abiotic controls on GHG production to determine the most significant factors affecting GHG flux from the floodplain. We found correlations between CO2 flux and soil temperature, organic matter content, and soil moisture, CH4 flux and pH, bulk density, inundation period length, soil temperature, and organic matter content. But minimal correlations between N2O flux and the measured variables. Spatially, our results demonstrate that constructed inset floodplains have higher global warming potential in the form of CH4 than any other site and for all other GHGs, potentially offsetting the positive benefits incurred by enhanced connectivity. However, at the reach scale, total CO2 flux from the soil remains the greater influence on climate since the area covered by these inset floodplains is comparatively much smaller than the rest of the floodplain. / Master of Science

Forests have the ability to sequester carbon from our atmosphere. Soil respiration (Rs) plays a role in a forest's ability to do so as it is a significant source of carbon dioxide back to the atmosphere. Therefore, understanding the process of Rs under varying conditions is gaining more attention. As of now we have a relatively good understanding of Rs under managed forest ecosystems such as pine plantations. This particular study examined Rs under different overstories and understories in a high elevation Southern Appalachian forest in order to get a better understanding of Rs under a natural hardwood system. The four vegetation types under consideration were an eastern hemlock (Tsuga canadensis L. Carriere) dominated overstory, a hardwood overstory with little to no understory, a mountain laurel (Kalmia latifolia L.) dominated understory, and a cinnamon fern (Osmundastrum cinnamomeum (L.) C.Presl) dominated understory. Differing temporal variations of Rs were observed under the vegetation types. We found monthly differences in rates among vegetation type however, an overall annual difference in Rs rates between vegetation types was not observed. This simply indicates the importance of observing Rs under different time scales to get a better understanding of its variation. We also calculated vegetation indices from remotely-sensed data to explore any relationships to Rs as well as if the indices themselves could improve out model. A vegetation index is a number that is calculated for every pixel in a remotely sensed image and represents plant vigor or abundance. Few significant relationships were found between the indices and Rs. Future work may want to better understand vegetation indices' spatial extent and accuracy in order to find whether they may be beneficial in Rs estimation. Understanding the influence of varying vegetation type and soil temperature and moisture on Rs will ultimately improve our ability to predict what drives changes in carbon fluxes. / Master of Science / Forests have the ability to sequester carbon from our atmosphere. Soil respiration (Rs) plays a role in a forest’s ability to do so as it is a significant source of carbon dioxide back to the atmosphere. Therefore, understanding the process of Rs under varying conditions is gaining more attention. As of now we have a relatively good understanding of Rs under managed forest ecosystems such as pine plantations. This particular study examined Rs under different overstories and understories in a high elevation Southern Appalachian forest in order to get a better understanding of Rs under a natural hardwood system. The four vegetation types under consideration were an eastern hemlock (Tsuga canadensis L. Carriere) dominated overstory, a hardwood overstory with little to no understory, a mountain laurel (Kalmia latifolia L.) dominated understory, and a cinnamon fern (Osmundastrum cinnamomeum (L.) C.Presl) dominated understory. Differing temporal variations of Rs were observed under the vegetation types. We found monthly differences in rates among vegetation type however, an overall annual difference in Rs rates between vegetation types was not observed. This simply indicates the importance of observing Rs under different time scales to get a better understanding of its variation. We also calculated vegetation indices from remotely-sensed data to explore any relationships to Rs as well as if the indices themselves could improve out model. A vegetation index is a number that is calculated for every pixel in a remotely sensed image and represents plant vigor or abundance. Few significant relationships were found between the indices and Rs. Future work may want to better understand vegetation indices’ spatial extent and accuracy in order to find whether they may be beneficial in Rs estimation. Understanding the influence of varying vegetation type and soil temperature and moisture on Rs will ultimately improve our ability to predict what drives changes in carbon fluxes.

Peatlands are a diverse type of wetland ecosystem, characterized by high levels of soil organic matter, that provide a wide array of ecosystem services including water storage and filtration, carbon sequestration, and unique habitats. Draining peatlands degrades their resilience to future disturbances, notably including high intensity, soil-consuming fires. Peat soil fires are unique in that they can smolder vertically through the soil column, with consequences ranging from large carbon emissions to altered hydrology and dramatic shifts in vegetation communities. In this work we had two complementary objectives to understand both the drivers and impacts of smoldering fires at the Great Dismal Swamp (VA and NC, USA). First, we developed and verified a new method to model peat burn depths with readily available water level and peat hydraulic property data. Our findings suggest that drainage weakens both short- and long-term controls on peat burn depths by reducing soil moisture and by decreasing peat water holding capacity. To address the impacts of smoldering fires, we quantified the abundance of the noxious Phragmites australis in a large fire scar and the extent to which altered hydrology influenced its occurrence. We did so by leveraging satellite imagery, random forest models, LiDAR data, and water table observations. Our results suggest that P. australis is aided by a hydrologic regime generated, in part, from the combined effects of drainage and deep smoldering fires. Our conclusions from these two studies contribute to the scientific understanding of smoldering peat fires and can inform management efforts. / Master of Science / Peatlands are a diverse type of wetland ecosystem that have characteristically thick levels of organic-rich soil, known as peat. Peatlands are home to a variety of unique plants and animals, store large amounts of carbon, and provide water storage functions. Peatlands were historically drained to enable development and conversion to other land usages, which had many unintended consequences like increasing their risk to wildfires that consume soil organic matter. An intense peat fire can smolder down through the peat, with impacts ranging from large releases of carbon to changes in water levels and vegetation communities. In this work we had two objectives aimed at understanding the drivers and impacts of smoldering peat fires in the Great Dismal Swamp (GDS) (VA and NC, USA). First, we developed and verified a new method of modeling how deep peat fires burn by using readily available water level and soil property data. Our findings suggest that drainage weakens both the short- and long-term controls on peat fire burn depths by reducing soil moisture and by limiting the ability of peats to hold water. We also studied how water levels in a post-peat consuming fire environment influence the amount of the weedy Phragmites australis. We did so by using satellite imagery, elevation data, and water table observations. Results from this investigation suggest that the combined effects of drainage and deep smoldering fires help to create ideal conditions for P. australis invasion and establishment. Our findings from these two studies add to the scientific understanding of smoldering peat fires and may inform land management decisions.

With the advent of the personal computer, mechanistic nutrient uptake models have become widely used as research and teaching tools in plant and soil science. Three models NST 3.0, SSAND, and PCATS have evolved to represent the current state of the art. There are two major categories of mechanistic models, transient state models with numerical solutions and steady state models. NST 3.0 belongs to the former model type, while SSAND and PCATS belong to the latter. NST 3.0 has been used extensively in crop research but has not been used with woody species. Only a few studies using SSAND and PCATS are available. To better understand the similarities and differences of these three models, it would be useful to compare model predictions with experimental observations using multiple datasets from the literature to represent various situations for woody species. Therefore, the objectives of this study are to: (i) compare the predictions of uptake by the NST 3.0, SSAND, and PCATS models for a suite of nutrients against experimentally measured values, (ii) compare the behavior of the three models using a one dimensional sensitivity analysis; and (iii) compare and contrast the behavior of NST 3.0 and SSAND using a multiple dimensional sensitivity analysis approach. Predictions of nutrient uptake by the three models when run with a common data set were diverse, indicating a need for a reexamination of model structure. The failure of many of the predictions to match observations indicates the need for further studies which produce representative datasets so that the predictive accuracy of each model can be evaluated. Both types of sensitivity analyses suggest that the effect of soil moisture on simulation can be influential when nutrient concentration in the soil solution (CLi) is low. One dimensional sensitivity analysis also revealed that Imax negatively influenced the uptake estimates from the SSAND and PCATS models. Further analysis indicates that this counter intuitive response of Imax is probably related to low soil nutrient supply. The predictions of SSAND under low-nutrient-supply scenarios are generally lower than those of NST 3.0. We suspect that both of these results are artifacts of the steady state models and further studies to improve them, such as incorporating important rhizospheric effects, are needed if they are to be used successfully for the longer growth periods and lower soil nutrient supply situations more typical of woody species. / Master of Science

Accurate measurement of soil moisture (SM) has a significant impact on agricultural production, hydrological modeling, forestry, horticulture, waste management, and other environmental fields. Particularly in precision agriculture (PA), high spatiotemporal resolution information about surface SM is crucial. However, the use of invasive SM probes and other sensors is expensive and requires extensive manpower. Moreover, these intrusive techniques provide point measurements and are unsuitable for large agricultural fields. As an alternative, this dissertation explores the remote sensing of surface SM by utilizing the surface reflectivity estimated from global navigation satellite systems reflectometry (GNSS-R) data acquired through smartphones and off-the-shelf, cost-effective U-blox global navigation satellite systems (GNSS) receivers. To estimate surface reflectivity, the GNSS receivers are attached underneath a small unmanned aircraft system (UAS), which flies over agricultural fields. Additionally, this dissertation investigates a fully custom UAS-based dual-polarized L-band microwave radiometric measurement technique over agricultural areas to estimate surface brightness temperature (����). The radiometer measures surface emissivity as ����, allowing for the estimation of surface SM while considering the detection and removal of radio frequency interference (RFI) from the radiometric measurements. This radiometer processes the data in near real-time onboard the UAS, collecting raw in-phase and quadratic (I&Q) signals across the study field. This feature mitigates the RFI onboard and significantly reduces post-processing time. In summary, this study highlights the utilization of smartphones and semi-custom GNSS receivers in conjunction with UAS-based GNSS-R techniques and UAS-based L-band microwave radiometry for the estimation of surface reflectivity and ����. The radiometric measurement of surface emissivity is related to surface reflectivity through the relationship (Emissivity = 1 -Reflectivity).

<p dir="ltr"><a href="" target="_blank">Watermelon [<i>Citrullus lanatus </i>(Thunb.) Matsum. & Nakai] is one of the world's top three most consumed fruits.</a> Indiana cultivates approximately 7,000 acres of watermelons every year, ranking 6^th in the nation. More than 70% of this production is concentrated in and around Knox County, making Southern Indiana a key region for watermelon production in the States. Despite its significance, watermelon production faces many challenges, including erratic rainfall patterns exacerbated by climate change. Enhanced irrigation management has emerged as a critical strategy in mitigating negative environmental effects and in optimizing fertilizer applications.</p><p dir="ltr">Currently, Southern Indiana farmers have incorporated different irrigation and fertilization practices into watermelon production, yet the effects on production outcomes remain poorly understood. To bridge this gap in knowledge, this study aims to explore the effects of existing practices on watermelon yield and develop irrigation guidelines for optimal production in the region. The experiment was conducted at Southwest Purdue Agricultural Center, Vincennes, Indiana, in 2022 and 2023. Four treatments were applied: High Irrigation, Low Irrigation, No Irrigation, and Fertigation. Fertigation treatment received the same water application as the High Irrigation treatment. Fertilizers were applied pre-plant in the High, Low, and No irrigation treatments, while frequent fertigation was applied to the Fertigation Treatment. Soil moisture sensors measuring volumetric water content were used for irrigation decisions. In 2022, the irrigation thresholds were set at 15% water depletion at 1-ft depth for High Irrigation and Fertigation treatment, and 2-ft depth for Low Irrigation. In 2023, the irrigation threshold for Low Irrigation was adjusted to 40% water depletion at 1-ft depth.</p><p dir="ltr">While soil moisture levels in the bed at the different depths varied notably among treatments, no significant differences in yield by weight were observed. The minimal impact of irrigation on watermelon yield suggests that rainfall provides sufficient water, preventing yield-reducing stress. However, the Fertigation and High Irrigation treatments yielded more fruit than the Low Irrigation and No Irrigation treatments. The dry periods in both years coincided with the watermelon fruit setting stages that may have contributed to the lower fruit set in the Low Irrigation and No Irrigation treatments. Fertigation showed a higher early yield than the other treatments in 2022. Analysis of soil and tissue nitrogen levels indicated that sole nitrogen application before planting could result in excessive soil nitrogen levels during vegetative growth. This excess nitrogen might delay flowering and harvest. This project offers insights into enhancing irrigation and fertilization practices for watermelon production in southern Indiana.</p>