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.

This study explored the improvement of individual performance outcomes within the administrative units of UNISA. The study aimed, in particular, to explore, analyse and interpret individual performance management practices. It should be noted that this study did not attempt to cover all the areas of effective and efficient performance management. The focus was to investigate the processes and approaches for continuously managing the improvement of individual performance outcomes, which could lead towards improved institutional performance. The main aim of the study was to investigate how the performance management system at the University of South Africa can be approved. The study adopted qualitative and quantitative research paradigms, thus a combination of inductive and deductive approaches, sampling and analyses, data collection and interpretations were used. However, the research design and methodology in this study primarily focused on a case study design and a mixedmethod approach to reach valid and reliable conclusions. The first part of the thesis focused on the analysis of literature and empirical documents relating to performance management approaches and the research design and methodology applied. The second part focused on the performance management practices at UNISA, the implementation of surveys/questionnaires, interviews and group-discussions. Lastly, ideas and themes were identified from the collected data that should answer the research questions. The study found that performance management should focus on the identification of an individual’s strengths and weaknesses in order to enable improved individual performance outcomes. Therefore, if managers want to manage individuals effectively and improve individual performance, all related factors, which include motivation, coaching and monitoring, as well as influencing positive behaviours by individuals, should form part of the effective performance management system. Far too often, managers neglect objectively analysing performance appraisals’ outcomes, and compromise by allocating undeserved percentage ratings, mainly to avoid possible conflict situations. The study’s findings provided valuable insights that could improve the performance management system at Unisa. - v - Some of the recommendations include: that effective performance management entails co-analysis, co-decision, co-design and co-evaluation, which could lead to the clear objective setting of targets for implementation by individuals; the implementation of quarterly appraisals; the implementation of ‘crowdsourcing’ or 360° evaluations; continuous self-development and training. This study’s outcomes could make a significant contribution to the body of existing literature in the discipline of Public Administration. More specifically, in respect of the survey/questionnaires within three prominent constructs, the triangulation and mixed-methods approach used for this study; and the case study model applied in the research of the University of South Africa, as an institution of higher education. / Public Administration and Management / D. Phil. (Public Administration)