京都大学 / 0048 / 新制・論文博士 / 博士(地球環境学) / 乙第12828号 / 論地環博第8号 / 新制||地環||24(附属図書館) / 31315 / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)准教授 西前 出, 教授 渡邉 紹裕, 教授 小方 登 / 学位規則第4条第2項該当 / Doctor of Global Environmental Studies / Kyoto University / DFAM

Urban trees are crucial to a healthy environment. The benefits range from good air quality to storm water management and public health. The aim of this thesis was to study urban trees in Umeå city. Umeå is in a process of densification and has a vision to increase in population to 200 000 by the year 2050. During densification, trees are often removed to make space for buildings and streets. To keep track of the trees in an urban area, an analysis of the share of canopy cover can be done. For this thesis, the city enter in Umeå has been analyzed to find out the share of trees, vegetation, imposturous ground, buildings, and water that makes up the land cover. This through a canopy cover analysis using the software i-Tree Canopy. The results show that the overall share of urban trees has decreased since 2007 and the share of buildings have increased, an evident effect of densification. In addition to analyzing canopy cover, the change in amount and location of municipally owned trees has also been analyzed. This analysis presented a contradictory view of urban trees, where the number of trees has increased. A reason for this could be that while the municipality has programs in place to plant and manage trees, privately owned trees are not being monitored. There are obstacles with the aim to increase the number of urban trees in a dense city. The increasing amount of imposturous ground and building makes the environment hard for trees to thrive in. The roots have not enough space to grow, and the trees are prone to damages. This results in trees that does not live very long before they have to be removed and replaced, which has negative effect on the environment. Preserving trees with large canopies and at the same time planting new ones are important parts in keeping a sustainable urban area. Analyzing canopy cover and the change over time is a way to learn and prepare for future urban planning in Umeå.

Cogongrass management generally requires multiple herbicide applications, however, success is limited if not integrated with other methods. Experiments were conducted to evaluate the use of cover cropping systems with herbicides on cogongrass control. Field studies determined that sequential glyphosate applications in the summer were necessary to achieve 80% or greater control, but a single application could be effective if weather conditions allowed early planting and good cover crop establishment of Roundup Ready soybeans. Studies also indicated that the use of ALS-resistant Italian ryegrass and white clover crop combinations showed no effect, but imazapyr applications made in May or June provided 80% or higher control by October. Greenhouse experiments showed that delayed planting at least 1 month after imazapyr preemergence applications from 70 to 280 g ae ha-1, significantly reduced emergence failure, height and biomass reductions of legumes used for revegetation.

Soil quality and health indicators are necessary to monitor and improve the agricultural sustainability. This experiment was conducted at Mississippi State, MS between 2015 and 2016. Soil samples were taken to determine bulk density, enzymatic activity, and total C and N. Results indicated greater bulk density, total C and N, and enzymatic activity for inter-row position than for within the corn row which was disturbed by strip-tillage. Soil bulk density tended to increase with soil depth; however, total C and N and total microbial activity decreased with depth both years. Total soil C and N increased from 2015 to 2016. Enzymatic activity was greatest at corn planting and decreased up thru four weeks apparently due to total C and N decomposition. Total C and N were related to bulk density and enzymatic activity because increase in soil C and N decreased the bulk density and increased the enzymatic activity values.

In recent years, green roofs have become an accepted solution in ecological urban design to mitigate the impacts of impervious surfaces (Berghage, Beattie, Jarrett, Thuring, & Razaei, 2009). An experimental research project was conducted at the Mississippi Agriculture and Forestry Experiment Station (MAFES) Green Infrastructure Research Area at South Farm of Mississippi State University to determine how medium depth and slope gradient on rooftops affect plant cover and survival. Plant cover was monitored monthly by photographing the experimental green roof platforms. Photoshop and AutoCAD software programs were employed to digitize and to calculate plant cover from the images. All recorded data was analyzed with Analysis of Variance (ANOVA) tests. It was determined that the effects of medium depth and slope are statistically significant on plant cover and survival.

Food production security and resiliency require combination of agricultural management practices that are environmentally friendly and economically viable. Cover crops and tillage are two typical management practices that influence corn (Zea mays L.) and soybean (Glycine max L.) production in Illinois and the Midwest, USA. Finding practices that could potentially reduce nitrous oxide (N2O) emissions and sequester carbon (C) in the soil can improve agricultural resiliency to climate change. Generally, shifting from reduced tillage (RT) to no-till (NT) improves soil structure and decreases C emissions or sequesters soil C but might increase N2O emissions. Including a legume cover crop such as hairy vetch (Vicia villosa L.) before corn is preferred to winter cereal cover crops (WCCCs) to avoid yield penalty in corn and ensure high grain production. Winter cereal cover crops such as winter cereal rye (Secale cereale) (WCR) could potentially decrease soil N2O emissions during fallow period by capturing residual N and reducing soil moisture. These conditions could change in soils with legacy tillage (RT vs. NT) effects due to changes in soil physical, chemical, and biological over time. We utilized a medium-term (six-year-old) trial to test several hypotheses. We hypothesized that RT increases the soil temperature, accelerates soil organic matter mineralization, and especially in combination with hairy vetch could increase soil N in the soil leading to increased corn grain yield and N2O emission (Chapter 1). We also hypothesized that WCR takes up residual N after harvesting corn, decrease soil N, use soil moisture, and therefore, could decrease soil N2O emission (Chapter 2). For study 1 (Chapter 1), our objective was to evaluate the influence of cover crop (hairy vetch) vs. a no CC control and tillage systems (RT vs. NT) on (i) corn yield, N uptake, removal, and N balance; (ii) N2O emissions during corn season; (iii) yield scaled N2O emissions on a long-term (eight years) tillage × cover cropping system during the corn growing season in 2019 and 2021. We also analyzed factors that influence N2O emissions via principal component analysis in corn season. In corn growing seasons, we found that corn grain yield was higher in RT than NT reflecting on more N in the soil in RT than NT. Hairy vetch increased corn grain yield, soil N, and N2O-N indicating increased corn grain yield by hairy vetch N contribution let to higher N loss. Yield-scaled N2O-N emissions in NT-2019 (3696.4 g N2O-N Mg-1) were twofold higher than RT-2019 (1872.7 g N2O-N Mg-1) and almost fourfold higher than NT-2021 and RT-2021 indicating in a wet year like 2019, yield-scaled N2O-N emissions were higher in NT than RT. Principal component analysis indicated N2O-N fluxes were less driven by soil N and more by environmental conditions and N balances reflecting on N application at planting in this trial. . The objectives for chapter 2 were to evaluate the legacy effect of tillage (RT vs. NT) and cover crops (WCR vs. a no cover crop control) on soil nitrate-N (NO3-N), volumetric water content (VWC), temperature, and N2O emission trends during a fallow period after corn in a six-yr trial. In spring 2020 we also estimated WCR biomass and N uptake as affected by tillage practices and compared WCR biomass to weeds in the no cover crop treatment. In rye growing season, winter cereal rye biomass was 55% higher than weeds in the fallow treatment. A linear positive relation between WCR biomass and N uptake (R2= 0.93) and C accumulation (R2 = 0.99) indicates WCR captures more N and adds more C inputs than weeds. Winter cereal rye biomass was also higher in RT than NT reflecting on higher soil temperature and N availability in RT than NT. Soil VWC was lower in WCR plots and there was a negative linear relation between days of the year (DOY) and VWC (R2 = 0.6). Despite all these differences, soil N2O-N values were mainly less than 5 g N2O-N ha-1d-1 in all sampling dates regardless of tillage or cover crop treatment. We conclude that in poorly drained Alfisols with claypan and fragipans, NT is not an effective strategy to decrease N2O-N fluxes. Hairy vetch benefits corn grain yield and supplement N but that increases N loss through N2O-N emissions. We concluded that we should focus on decreasing N2O emissions early in corn season since majority of N is lost during that time sometimes 300 times higher than those reported during the WCR phase. Some changes in management practices that could reduce N2O losses are shifting from upfront N application to sidedress N management, terminating hairy vetch at or even after corn planting, and combine these efforts with enhanced efficiency fertilizers that control nitrification and denitrification.

Integrated crop-livestock systems (ICLS) incorporate cropping systems and livestock production by grazing cover crops. With a growing awareness in recent years regarding agricultural sustainability, these systems have begun to be re-introduced into the southeastern U.S. This study evaluated cover cropping systems under grazed no-till (GNT), un-grazed no-till (UNT), and un-grazed conventional tillage (UCT) management, in Mississippi. Beef cattle (Bos spp.) performance was significantly less in the cover crop treatment of oats (Avena sativa) + crimson clover (Trifolium incarnatum) + radish (Raphanus sativus; OCR) in both average daily gain (ADG; 3.03 lb hd-1 d-1) and total gain ac-1 (GAIN; 346 lb ac-1). Soybean (Glycine max) yield was unaffected by cover crop treatment and tillage. The lowest expected economic return was generated by OCR ($749.31 ac-1). Soil penetration resistance was unaffected by the influence of grazing. The greatest concentrations of soil organic carbon (1.44%) and soil nitrogen (0.20%) were observed in GNT.

The exact cover problem is an NP-complete problem with many widespread use cases such as crew scheduling, railway scheduling, benchmarking as well as having applications in set theory. Existing algorithms can be slow when dealing with large datasets however. To solve this problem in a quick manner this thesis uses a new method based on an existing algorithm called Algorithm X utilizing parallelization with the task construct of OpenMP to produce better results, at best providing a speedup of 4.5 when compared to a serial optimized implementation of Algorithm X. Since creating child tasks through the task construct causes additional overhead this thesis examines the effect granularity has on the solver by varying how many child tasks should be created before opting to solve the rest of the problem serially. The optimal number of child tasks is found to be very low when using a high amount of cores and vice versa when using fewer cores. Since the new method created for this thesis can solve the exact cover problem faster than Algorithm X it can prove to be beneficial when solving the problems mentioned earlier.

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