As urbanization increases globally, habitat loss is increasing at an unprecedented rate, eroding the suitability of many landscapes for most forms of wildlife, including bees. At least some of this habitat loss is through the ongoing expansion of urban areas, a process termed ‘urbanization’. Studies of the effects of urbanization and urban land use on bees have reported a mixture of results, including some instances where at least some species appear to do better in urban areas than they do in lands surrounding urban areas. While the impacts of urbanization on bee communities has been investigated, tree canopy cover has been largely overlooked as a contributor to urban bee distributions, despite their potential importance as a predictor of bee activity. I investigated the impacts of urban land use and tree canopy cover on bee communities across a variety of neighbourhoods in a medium-sized Canadian city (Ottawa, Ontario). In total, I surveyed bee communities in 27 residential yards that varied in terms of the degree of urban land use (measured as percent impervious surface area) and tree canopy cover (percent deciduous canopy cover) across a range of spatial scales. Using linear regression and model selection, I determined that bee abundance was negatively correlated with the degree of urban land use surrounding a yard, and positively correlated with the richness of the local (i.e., yard) flowering plant community. Yard floral richness, but not urban land use or tree cover, was also a predictor of the diversity of the bee community visiting the yard. In fact, tree canopy cover did not factor in any of the top models predicting either bee abundance, richness, or diversity. My results support the idea that urban land use could negatively impact bee communities, but also suggest that landscaping and urban planning decisions that maximize local floral richness could counteract some of the negative impacts of urbanization on bee populations.

Indiana University-Purdue University Indianapolis (IUPUI) / Nitrous oxide (N2O) is an atmospheric constituent that contributes to climate warming and stratospheric ozone depletion. A large fraction of the anthropogenic N2O emission originates from agricultural soils suggesting therefore a strong connection between N2O accumulation in the atmosphere and agricultural land management. During the last 2-3 decades, no-till (NT) farming and integration of cover crops into crop rotation represent two major developments in agriculture, but much remains to be learned about the impact of these management approaches on N2O emission and underlying biological soil factors. This dissertation focuses on the contribution of different components of the soil microflora to N2O production, and how different types of cover crops (legume vs grass) affect the soil microbial community composition, mineral N availability, and N2O emission in plowed (PT) and NT soils. To address these questions, several laboratory and greenhouse experiments were conducted. Results of these experiments documented soil microbial community responses to cover crop addition and could inform the selection of cover crops most suitable to soils under different tillage practices.

The occurrence of herbicide resistance weeds across the southern United States has been increasing. Research is needed to develop alternative control measures, while supporting sound agronomic practices. Greenhouse and field studies were conducted to evaluate cereal cover cropping techniques along with novel herbicides to determine their value for Mississippi growers. Field studies were performed to determine which combination of cereal cover crops (cereal rye, wheat and oats) and residual herbicides (S-metolachlor + metribuzin, S-metolachlor + fomesafen, pendimethalin, flumioxazin, sulfentrazone + metribuzin and pyroxasulfone + flumioxazin) would maximize soybean yield in the presence of weeds. Cereal cover crop termination methods were evaluated and a partial budget was generated to examine the total costs of growing soybeans utilizing cereal cover crops and residual herbicides. Residual herbicide applications averaged across all cereal cover crops controlled Amaranthus spp. greater than 89% by 28 DAT. Control by the cover crops alone was 67% for of Amaranthus spp. In all cereal species tested, cutting the cover crops 10 cm above the soil and leaving the residue reduced weed numbers compared to other termination methods. However, high production and implementation costs may prevent widespread adoption of cereal cover crops and residual herbicides in Mississippi. Aminocyclopyrachlor (AMCP) is a synthetic auxin herbicide currently labeled for non-crop use, but has characteristics which may make it useful as a preplant burndown (PPB) herbicide. The application of AMCP prior to planting of corn and cotton were evaluated and carryover effects to soybean were also evaluated. Tank mix combinations of AMCP with residual herbicides (rimsulfuron, flumioxazin, pyroxasulfone, pyroxasulfone+ flumioxazin and atrazine) were also evaluated. A rate titration of AMCP and its impacts on crop species were evaluated in the greenhouse. Corn showed tolerance to AMCP except at 0.28 kg ai ha-1 applied prior to planting. Cotton was sensitive to AMCP as rate increased closer to the planting date, but response depended upon soil texture. AMCP impacts on soybean showed greater sensitivity (90% injury) then all other species evaluated. Due to potential impacts on soybean and cotton, AMCP is not a potential PPB for use in Mississippi.

Mid-southern USA soybean [Glycine max (L.) Merr.] producers are being pushed to increase adoption of conservation tillage systems as a means of increasing the application efficiency of gravity flow irrigation systems. This research was conducted to determine whether the efficiency of furrow-irrigation systems could be manipulated through conservation tillage systems while maintaining soybean productivity and profitability. Three experiments were conducted near Stoneville, MS on a Dubbs silt loam (Fine-silty, mixed, active, thermic Typic Hapludalfs) to determine the effects of reducing tillage and increasing ground cover residues on irrigation application efficiency, irrigation water use efficiency, soybean grain yield, and net returns above specified costs. In experiment 1, transitioning from conventional tillage to a conservation tillage system had no adverse effect on irrigation application efficiency, irrigation water use efficiency, soybean grain yield, or net returns above specified costs when subsoiling was included. For experiment 2, replacing subsoiling with a cereal rye or tillage radish cover crop in a conservation tillage system either had no effect or reduced irrigation application efficiency, irrigation water use efficiency, soybean grain yield, and net returns above specified costs up to 41%. In experiment 3, independent of cover crop, reducing tillage to only furrow creation had no adverse effect on irrigation application efficiency, irrigation water use efficiency, soybean grain yield, and net returns above specified costs relative to a conservation tillage system with subsoiling. Conservation tillage systems that include subsoiling maximize irrigation application efficiency and irrigation water use efficiency while minimizing adverse effects on yield and net returns relative to conservation tillage systems that further reduce tillage and/or increase ground coverage with cover crops. Our data indicate that soybean producers in the mid-southern USA maximize furrow-irrigation functionality, yield, and profitability while minimizing risk by transitioning from a conventional tillage system to a conservation tillage system with subsoiling.

Cover crops and composted broiler litter (CBL) are two organic methods used to improve soils and organic vegetable production. The objectives of this study included determining the extent summer cover crops and CBL alter nutrient availability in soil, determining how summer cover crops and CBL influence fall vegetable crops in organic production systems and identifying which cover crops/ CBL combinations improve fall vegetable crop production best. Four cover crops were tested: sunn hemp (Crotalaria juncea), sesame (Sesamum indicum), sorghum sudan grass (Sorghum X drummondii) and a sunn hemp + sesame blend, in combination with four composted broiler litter rates: 0, 2,800, 5,600, 11,200 kg.ha-1 for two years. Few differences were seen among cover crop treatments except for the sorghum sudan grass treatment, which had negative effects on fall broccoli production unless combined with CBL. The CBL increased nutrient availability, percent organic matter, pH and broccoli yield as the rate increased.

No description available.

A pebble distribution places a nonnegative number of pebbles on the vertices of a graph G. In graph rubbling, the pebbles can be redistributed using pebbling and rubbling moves, typically with the goal of reaching some target pebble distribution. In graph pebbling, only the pebbling move is allowed. The cover pebbling number is the smallest k such that from any initial distribution of k pebbles, it is possible that after a series of pebbling moves there is at least one pebble on every vertex of G. The Cover Pebbling Theorem asserts that to determine the cover pebbling number of a graph, it is sufficient to consider the pebbling distributions that initially place all pebbles on a single vertex. In this paper, we prove a rubbling analogue of the Cover Pebbling Theorem, providing an answer to an open question of Belford and Sieben (2009). In addition, we prove a stronger version of the Cover Rubbling Theorem for trees.

Early planting soybean (Glycine max L.) strategies across the mid-southern United States has complicated weed management in the form of post-harvest weed control. Research has investigated the use of cover crops to aid in management of weed populations during winter months, but conventional cover crops provides minimal weed management benefit immediately following cash crop harvest. Inter-seeding cover crop into crop canopies has potential to promote earlier cover crop establishment, thus creating higher potential for post-harvest weed management. However, factors such as inter-seeding timing, herbicide residue, as well as harvest aid applications must be considered. Therefore, studies were conducted in Mississippi in 2017, 2018, and 2019 to determine if cover crops inter-seeded through soybean could improve weed control used in conjunction with common management strategies in Mississippi production systems. Conclusions drawn from these studies indicate inter-seeded cover crops can be utilized in soybean production systems to improve weed management after harvest.

In northeastern Mississippi, land cover types vary from agriculture, forests, urban surfaces, pasture, to bodies of water. Substantial evidence exists supporting the contribution of land cover and land cover discontinuities, or physiographic transition zones, to cloud formation on synoptically benign days in many areas across the globe. However, research is lacking on the specific type of land cover and/or land cover discontinuities that convection favors in the warm season. The objective of this study was to develop a synoptically benign convective cloud climatology for northeastern Mississippi and compare this climatology to land cover to determine whether a relationship between land cover type and convective cloud enhancement exists. The study shows a statistically significant clustered pattern occurring in the study area. In addition, enhanced convective events appear to favor land use regions of evergreen needleleaf forest; dryland, cropland, and pasture; and savanna. The study indicates that these three land cover types occur significantly more frequently for the enhancement points than in the study area. The findings support the existence of a significant relationship between land cover and convective enhancement in northeastern Mississippi and provide opportunities for additional future research on relationships between land cover and convection to improve forecast applications and our knowledge of mesoscale circulations.

Cover crops (CC) can contribute to production in pastures, but the diversity of CC mixtures and defoliation frequency (DF) may alter productivity. A 2-yr experiment conducted at Raymond, MS, quantified CC × DF effects on forage mass (FM) and nutritive value of winter CC and subsequent summer hay production. Treatments were factorial combinations of 10 CC (using several species of grasses, legumes, and brassicas) and three DF (harvested every 4 or 8-wk or cut and left as mulch) in a split-plot arrangement of a randomized complete block design experiment with three replications. Generally, mixtures with legumes had greater FM and better nutritive value. Summer hay production did not respond to difference in CC composition, however, harvesting of CC reduced summer hay but increased year-long FM. These results suggest that CC when harvested can contribute to forage production with improved nutritive value and can increase year-long FM, but summer hay production can benefit when the CC is left as mulch.