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Call number: LD2668 .T4 1964 B82 / Master of Science

Row crop production can be characterized by constant change. Agricultural technology is responsible for most of the changes in productivity observed at the field level since the advent of mechanized farm equipment. Genetically modified (GM) cotton varieties have changed many aspects of cotton production in the United States. The advent of GM varieties has been the source of altered cropping practices in cotton production. The rapid adoption of GM cotton varieties in Mississippi has allowed producers to alter certain aspects of their farming operation because of added flexibility, increased yields, and other benefits of GM varieties. This study analyses the effects of certain changes in some of the most relevant components of cotton production on yield that stem from the adoption of GM varieties in Mississippi by estimating and comparing regional production functions from 1996 to 2005.

Corn (Zea mays L.) and cotton (Gossypium hirsutum) are globally important crops for food, feed, fuel, and industrial feedstocks. In Eastern Virginia, achieving optimal yields is challenging due to unpredictable environmental conditions which impact overall crop growth and nutrient use efficiency. More data are needed on adaptative corn management strategies that focus on increasing nutrient use efficiencies and crop yields (i.e., 4R nutrient management, biostimulants, and in-season crop protection chemicals). With less than 5% of Virginia's corn and cotton fields irrigated, increased irrigation adoption could stabilize/increase crop production outcomes in this region. Three studies were conducted to evaluate these management strategies with the following objectives: 1. To compare standard farmer practices with the Adaptive Corn Management System (ACMS) using a treatment omission/addition approach. 2. To analyze subsurface drip irrigation (SDI) effects on corn grain yield under different seeding and nitrogen (N) application rates in drought-prone soils of Eastern Virginia. 3. To evaluate SDI strategies in cotton, assessing the effects of dripline spacing, plant growth regulator (PGR) rates, irrigation strategies, N rates, and variety on yield. The first study integrated irrigation, in-season nutrient supplementation (soil and foliar applied), foliar fungicides, and biostimulants to enhance corn yields. Field trials conducted across five Virginia locations (2022 to 2023) with irrigated and non-irrigated sites showed yield improvements with supplemental nutrients, biostimulants, and fungicides in 4 of 10 experiments. The yield increase resulting from irrigation in intensive and standard management strategies ranged from -3 to 61%, averaging 8.9 and 34% for intensive and standard management practices, respectively. The second study (2022-2024) evaluated six SDI management strategies, four seeding rates (59,280 to 103,740 plants ha-1), and four N application rates (133 to 333 kg N ha⁻¹). Main effects of irrigation, seeding, and N rates significantly impacted yields. Irrigation and N interactions were significant across years for grain yield. Corn grain yield was greater by 102% with irrigation in 2022 compared to only 13%, and 51% in 2023 and 2024. Averaged over the three years the 0.91 m dripline and 0.91 m with volumetric water content (VWC) sensors increased revenue by $985 and $885 ha-1, respectively, above non-irrigated. Grain yield increased up to a seeding rate of 88,920 plants ha-1 and N rates up to 267 kg N ha-1. The third study utilized two experim¬¬¬¬¬ents evaluating SDI management strategies in cotton from 2019 - 2021. Experiment 1 of the third study tested three irrigation systems with various dripline spacings (0.91 m, 1.82 m, non-irrigated), four PGR rates (0%, 100%, 150%, 200% of current Virginia recommendations, and four cotton varieties. Experiment 2 examined three irrigation strategies (irrigation, fertigation, and non-irrigated), three N rates (89, 133, 178 kg ha-1), three PGR rates (0, 100 and 200%), and two cotton varieties. Results from experiment 1 showed that dripline spacing significantly influenced lint yields in 2 of 3 years. The PGR application rates significantly influenced lint yield in 2021 growing season only. Lint yield varied by variety in 3 of 3 years of the study. The 1.82 m dripline and 100% PGR rate produced the highest economic gains of $158 and $162 ha-1 respectively above check. In Experiment 2, the lint yield varied by irrigation all three years, while PGR rates, N application rates, and variety each influenced lint yield in 2 of 3 years. The highest rates of lint yield increase were achieved at 133 kg N ha-1. Irrigation implementation was more effective in increasing corn grain yields than cotton lint yields during the six-year study period. Corn grain yields were increased on average 60% with SDI compared to non-irrigated treatments over the three-year study. Inputs for adaptative corn management systems were not consistent for increasing grain yields. Although various PGR rates were evaluated, current PGR recommendations for cotton are sufficient with the varieties evaluated in maximizing lint yields. The current N applications for Virginia were in-line with those of the current study which identified 133 kg N ha-1. These studies provide the first data for corn and cotton management with SDI in Virginia and the Mid-Atlantic USA. / Doctor of Philosophy / Corn (Zea Mays L.) and cotton (Gossypium hirsutum) are essential crops globally, providing food, feed, fuel, and industrial materials. In the U.S., 36.7 million hectares of corn and 4.52 million hectares of cotton are grown annually, with Virginia cultivating 186,234 hectares of corn and 36,800 hectares of cotton. Most of these crops in Virginia are grown without irrigation on sandy soils with low nutrient and moisture retention coupled with regions non-uniform precipitation with heavy summer/fall rains which reduce nutrient efficiencies and destabilize yields. While practices like in-season nutrient application (4-R strategy), fungicides, and biostimulants can improve yields, they are not common practices in Virginia. For these practices to be part of adaptive corn management systems, their effectiveness under local conditions needs to be evaluated. The limitations to irrigation in Virginia are largely due to farmers reliance on high annual precipitations, and state restrictions on water withdrawals, desiring that any irrigation system to be adopted to be efficient and flexible for deficit irrigation. Making the SDI the better choice but for it to be adopted, more information is needed. Additionally, understanding how factors like irrigation, seeding rates, plant growth regulators (PGRs), and modern cotton varieties interact with nutrient management under the sub-surface drip irrigation (SDI) system is essential for improving productivity and sustainability of these crops. This research aimed to develop advanced corn and cotton production systems for Virginia by addressing these challenges and evaluating effective crop management strategies. 1) To compare standard farmer management practices (control) and intensive management (attempting to address common yield-limiting factors) with the ACMS using a treatment omission/addition experiment (study one). 2) To assess the impact of subsurface drip irrigation (SDI) strategies on corn grain yield in Virginia and analyze how different seeding and nitrogen (N) rates affect yield under different subsurface drip irrigation strategies in drought-prone soils of Eastern Virginia (study two). 3) a) To evaluate the effects of different dripline spacings and plant growth regulator (PGR) rates on the growth and yield of various cotton varieties, 3) b) Assess the influence of different irrigation strategies, N rates, PGR rates, and modern upland cotton varieties on yield and quality (study three). The first study found that adding biostimulants, foliar fungicides additional phosphorus and potassium and additional sidedress nitrogen variably increased corn grain yield in 3 out of 10. The significant differences between standard and intensive management were observed in 3 of 10 experiments. Addition of extra P and K, sidedress N, and biologicals to the standard management under the non-irrigated conditions resulted in a 15% relative yield increase compared to the irrigated conditions. On average, irrigation increased grain yields by 8.9% under intensive management and 34% under standard management, with yield improvements ranging from -3% to 38% and 14% to 61%, respectively, over non-irrigated fields. In the second study, grain yield was significantly influenced by main effect of irrigation, nitrogen, and seeding rates with notable interactions between irrigation and nitrogen across the years (2022-2024) at P≤ 0.1. The highest impact of irrigation was observed in 2022 with yield increase up to102% over non-irrigated compared to only 13%, and 51% in 2023 and 2024 respectively. Over the three years of this study, the grain yield gains were greatest when a 0.91 m dripline spacing was used which averaged 4,106 kg ha-1 above non-irrigated yielding an economic gain of $985 ha-1. Results from study one of the third experiment which evaluated the effects of upland cotton cultivars, irrigation, and PGR rates on lint yield, showed significant differences in lint yield due to variety across three years. Irrigation influenced lint yield in 2 of 3 years (2020 and 2021), while PGR rates caused yield variation only in 2021. Averaged over three years, the highest yields gains were observed using a 1.82 m dripline, and 100% PGR rate, yielding $158 and $162 in economic gains above the respective checks. In the second experiment of the third study, lint yield varied by irrigation treatments in all the three years, while PGR, N application and variety, each influenced lint yield only 2 of the 3 years of the study. The highest increase in yield due to N application rates was attained at 133 kg N ha-1 with no statistically significant results observed at 279 kg N ha-1 when compared to 133 kg N ha-1. With the exception of interaction between irrigation and variety in experiment 1 (2021), and PGR rates and N rates in experiment 2 (2021), no other significant interactions were observed for lint yield. The findings from the study one showed that balanced N, P, and K supplementation, alongside biostimulants and fungicides could maximize corn yields in dynamic farming conditions. Irrigation was the major driver to yield advancement. The results from the second and third study showed that subsurface drip irrigation (SDI), particularly with a 0.91- m dripline spacing, can significantly improve corn yield, while 1.82 m dripline can enhance the cotton yield in Virginia and the mid-Atlantic. It was not economical to increase the PGR application rates beyond the 100% PGR rate of the recommended Virginia Cooperative Extension (VCE). Additionally, optimized irrigation, PGR management, and precise nitrogen application are key to achieving high yields in modern cotton varieties, ensuring efficient and resilient production systems.

Submitted by (edna.saturno@ufrpe.br) on 2016-11-28T14:10:41Z No. of bitstreams: 1 Mariana Oliveira Breda.pdf: 588678 bytes, checksum: dfbffb2bf31e84d654f1e337dae28971 (MD5) / Made available in DSpace on 2016-11-28T14:10:41Z (GMT). No. of bitstreams: 1 Mariana Oliveira Breda.pdf: 588678 bytes, checksum: dfbffb2bf31e84d654f1e337dae28971 (MD5) Previous issue date: 2011-02-01 / Aphis gossypii Glover is one of the major pest of cotton in Brazil, causing direct and indirect damage through viruses transmission. In alternative production systems, the control of this pest is carried out by natural biological control and by application of botanical insecticides. However, the performance of A. gossypii, its natural enemies and insecticides may be affected by different features of cotton cultivars, as the tricomas density. The objectives of this study were examine the interactions between white (BRS 8H and BRS 201) and colored fiber cotton cultivars (BRS Verde, BRS Safira and BRS Rubi), botanical insecticide (Azamax®, castor bean oil emulsion, aqueous extract of neem seeds, Eucalyptus citrioda Hook and E. staigeriana essential oils), A. gossypii and its natural enemy Cycloneda sanguinea (L.).Tested cultivars did not influence the development and feeding preference of A. gossypii, the locomotion and search ability of C. sanguinea and the effectiveness of tested botanical insecticides. The essential oils of E. staigeriana e E. citriodora showed no decrease in pest population and caused severe phytotoxicity in all cotton cultivars. Azamax® showed A. gossypii mortality ranging between 64 and 100%, and negative instantaneous growth rate (ri), from the concentration of 1.25%. For aqueous extract of neem seeds aphid mortality ranged between 12 and 92% and the ri was negative from concentration above 2.5%. Castor bean oil emulsion had low toxicity, with mortality rates ranging between 8 and 68% and negative ri, from concentration of 3.0%. Azamax® 0.25 and 1.25%, aqueous extract of neem seeds 2.25% and castor bean oil emulsion 3.0% showed high mortality to larvae of the 1st and 4th instars of C. sanguinea preventing the emergence of adults. / Aphis gossypii Glover constitui uma das principais pragas do algodoeiro no Brasil, causando danos diretos e indiretos através da transmissão de viroses. Em sistemas alternativos de produção, o controle dessa praga é mediado pelo controle biológico natural e a aplicação de inseticidas botânicos. Entretanto, a ação desse inseto, dos seus inimigos naturais e dos inseticidas utilizados pode ser influenciada por características das cultivares de algodoeiro, como a densidade de tricomas. Os objetivos desse trabalho foram analisar as interações de cultivares de algodão de fibra branca (BRS 8H e BRS 201) e colorida (BRS Verde, BRS Safira e BRS Rubi), inseticidas botânicos (Azamax®, extrato aquoso de nim, óleo de mamona e óleos essenciais de Eucalyptus staigeriana Hook e E. citriodora), A. gossypii e Cycloneda sanguinea (L.), um dos principais inimigos naturais desse pulgão no Brasil. Observou-se que de maneira geral, as cultivares testadas não influenciaram o desenvolvimento e a preferência alimentar de A. gossypii, a locomoção e capacidade de busca de C. sanguinea e a eficiência dos inseticidas botânicos testados. Os óleos essenciais de E. staigeriana e E. citriodora não provocaram redução na população da praga e causaram intensa fitotoxidade em todas as cultivares de algodão. Azamax® apresentou mortalidade de A. gossypii, entre 64 e 100%, e taxa instantânea de crescimento (ri) negativa, a partir da concentração de 1,25%. Para o extrato aquoso de nim a mortalidade variou entre 12 e 92% e as ri foram negativas, a partir da concentração de 2,5%. O óleo de mamona teve baixa toxicidade, com mortalidade variando entre 8 e 68% e ri negativas a partir da concentração de 3,0%. Azamax® a 0,25 e 1,25%, extrato aquoso de nim a 2,25% e óleo de mamona a 3,0% causaram mortalidade elevada para larvas de 1° e 4° ínstares de C. sanguinea, inviabilizando a emergência de adultos.