Conservation tillage production systems for flue-cured tobacco (Nicotiana tabacum L.) have been studied for many years. Inadequate chemical weed control and lack of acceptable pesticide and fertilizer application resulted in consistently lower yields and inferior cured leaf quality. The development of new conservation tillage equipment, improved methods of fertilizer application, and new herbicides, have resulted in a renewed interest in conservation tillage labeled for tobacco. This research investigated management practices to address slow early season growth characteristic of strip-tillage tobacco production. Objectives of the first study were to evaluate the methods of starter fertilizer application and determine the optimal rate. A transplant water treatment (11 kg ha⁻¹) and 3 rates (11, 22, and 45 kg ha⁻¹) of injected 9-45-15 (N:P₂O₅:K₂O) water soluble starter fertilizer were evaluated for early season plant growth and time of topping. Starter fertilizer treatments increased tobacco root weight by 22% and leaf area up to 41%. Earlier topping was observed as a result of starter fertilizer with 23 and 6% more plants topped during the initial topping date in 1999 and 2000, respectively. Starter fertilizer did not consistently increase the yield of either strip-tillage or conventional tillage tobacco. The objectives of the second study were to compare the use of raised beds with flat-planting and investigate cover crop residue management techniques. Residue management treatments minimized residue within the strip-tilled area with an early hooded spray application (strip-killed) of a burndown herbicide as opposed to the traditional broadcast burndown application. The use of raised beds for strip-tillage production of tobacco showed no clear benefit when compared to flat-planting. Strip-tillage plots were similar to conventional tillage for cured leaf quality and yield. Early season strip-kill burndown herbicide applications proved beneficial in reducing difficulties incorporating residue into the strip-tilled area thus improving the quality of the prepared seed bed. This research has added to the present knowledge regarding strip-tillage tobacco production, and refined necessary cultural practices. Transplant starter fertilizer is recommended to overcome the typical slow early season growth characteristic of strip-tilled tobacco. However, increased rates (greater than 11 kg ha⁻¹) or under-row injection of the material had no added benefit. The research also demonstrated that the use of raised beds should not be considered a necessary practice with the use of a strip-till implement that incorporates under-row subsoil tillage. This research has demonstrated that tobacco yields and quality comparable to conventional tillage can be realized using strip-tillage production techniques. / Master of Science

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.

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Soil-borne oomycetes include plant pathogens that cause substantial losses in the agricultural sector. To better manage this important group of pathogens, it is critical to understand how they respond to common agricultural practices, such as tillage and crop rotation. Here, a long-term field experiment with a split-plot design with tillage as the main plot factor (conventional tillage [CT] vs. no till [NT], 2 levels) and rotation as the subplot factor (monocultures of soybean, corn, or wheat, and corn-soybean-wheat rotation, 4 levels) was sampled. Post-harvest oomycete communities were characterized over three consecutive years (2016-2018) by metabarcoding the Internal Transcribed Spacer 1 (ITS1) region of soil DNA extracts. The community contained 292 Amplicon Sequence Variants (ASVs) and was dominated by Globisporangium spp. (85.1% in abundance, 203 ASV) and Pythium spp. (10.4%, 51 ASV). NT decreased diversity and community compositional structure heterogeneity, while crop rotation only affected the community structure under CT. Soil and crop health represented by soybean seedling vitality was lowest in soils under CT cultivating soybean or corn, while grain yield of the three crops responded differently to tillage and crop rotation regimes. The interaction effects of tillage and rotation on most oomycetes species accentuated the complexity of managing these pathogens.

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Horseweed has been documented in 70 countries and 40 different crops around the world and is listed as being a problem weed in no-till production systems. Horseweed has developed resistance to many herbicide modes of action including glycine. Field experiments were conducted from 2004 to 2006 in the Mississippi Delta to evaluate the field emergence of horseweed and most effective treatment programs for its control. Field emergence of horseweed was observed occurring primarily in the fall of the year, September through early November, when temperatures were between 15.6 to 23.4 C with later flushes occurring from late January through early April with temperatures ranging from 5.2 to 16 C. Tillage in September followed by herbicide in March gave 100% control of horseweed across all locations. Glyphosate + 2,4-D and glyphosate + dicamba were the best glyphosate-based treatments and provided 90% or better horseweed control 4 WAT both years. Glufosinate-based burndowns provided 81 to 97% horseweed control and soybean yields were generally similar with all glufosinate-based programs.

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