2021-01-252021-01-252020-122020-12December 2https://hdl.handle.net/2346/86741Project 1: Potential of Biochar Application to Mitigate Salinity Stress in Eggplant Salt stress is one of the major environmental stresses predominant in arid and semi-arid areas of the world. In these regions, deteriorating quality of groundwater and cultivation practices have resulted in increased accumulation of salts in the root zone. The presence of excess salts in the root zone is detrimental for plant growth and economic yield. Recently, biochar has received great consideration as a soil amendment to mitigate the detrimental effects of abiotic stresses. However, the effectiveness of biochar to mitigate the salinity stress depends on the feedstock type, pyrolysis temperature and time, soil type and properties, and plant species. Therefore, a pot experiment in a greenhouse was conducted to (1) examine the effects of salinity stress on physiology, shoot and root growth, and yield of eggplant (Solanum melongena L.), and (2) evaluate the potential of hardwood biochar and softwood biochar to mitigate the damaging effects of salinity stress on eggplant. The experiment was conducted in a split-plot design with three salinity levels of irrigation water [S0 (control, 0.04 dS m-1), S1 (2 dS m-1) and S2 (4 dS m-1)] as main-plot factor and three biochar treatments [B0 (control, non-biochar), Bh (hardwood biochar) and Bs (softwood biochar)] as sub-plot factor with four replications. Results showed that stomatal conductance and photosynthesis rate decreased significantly, while leaf temperature and electrolyte leakage increased significantly with increase in irrigation water salinity levels. Root growth (root length density and root surface area density), shoot growth (plant height, stem diameter, and leaf area) and yield of eggplant declined with increase in levels of salinity stress. A decrease in plant growth with increased levels of salinity of irrigation water can be ascribed to increased osmotic stress and reduced water uptake by plants in higher salinity treatments, which is evident from reduced stomatal conductance in higher salinity treatments. Biochar application increased soil water availability and salt leaching, which may have caused the dilution of comparatively concentrated soil solution in the root zone. Thus, biochar addition reduces osmotic stress and enhances the plant water uptake for better plant growth. Biochar application helped to enhance stomatal conductance and photosynthesis rate, and to decrease leaf temperature and electrolyte leakage in leaf tissues of plants resulting in better root growth, shoot growth, and fruit yield of eggplant in treatments amended with biochar than non-biochar (control) treatment. There was no significant difference in the effect of two types of biochars (hardwood and softwood biochar) on physiology, root growth, shoot growth, and yield of eggplant. Therefore, it can be concluded that softwood and hardwood biochars could be used to minimize the detrimental impacts of salinity stress in eggplant. Project 2: Cucumber production under deficit irrigation Water shortage is increasing in the most regions of the world, which is creating a challenge to sustain crop production especially in arid and semi-arid regions such as Southern High Plains (SHP) of the United States (US). There is a need to identify and adopt the irrigation management practices which can help to conserve water and to sustain crop production in water limited regions. A two-year field study was conducted during the summers of 2019 and 2020 to evaluate the effect of deficit irrigation levels and cultivars on physiology, plant growth, root distribution pattern, soil water depletion, yield and water use efficiency (WUE) of cucumber (Cucumis sativus). The experiment was conducted in a split-plot design with four irrigation levels (100% ETc (crop evapotranspiration), 80% ETc, 60% ETc, and 40% ETc) as main plot factor and two cultivars (Poinsett 76 and Market More 76) as sub plot factor with three replications. Gas exchange parameters [photosynthesis rate (Pn), stomatal conductance (gs), transpiration rate (E), intercellular CO2 concentration (Ci), stomatal limitations, intrinsic water use efficiency (WUEi)] and relative leaf temperature were found to be comparable between 80% ETc and 100% ETc. However, severe water deficit in 60% ETc and 40% ETc irrigation levels negatively impacted the aforementioned gas exchange parameters and relative leaf temperature when compared to 100% ETc. Leaf area was also negatively affected by the severe water deficit in 60% ETc and 40% ETc irrigation levels. Overall, photosynthesis per plant decreased significantly in 60% ETc and 40% ETc compared to 100% ETc due to decrease in both Pn and leaf area, which subsequently caused a significant decline in plant growth and yield in 60% ETc and 40% ETc when compared to 100% ETc. However, both Pn and leaf area were comparable between 100% ETc and 80% ETc; therefore, photosynthesis per plant was similar between them which lead to comparable plant growth and yield between them. Market More 76 had higher Pn, gs, E, and Ci while it had lower stomatal limitations, WUEi and relative leaf temperature compared to Poinsett 76. Because of higher leaf area and Pn, Market More 76 produced considerably higher vegetative dry biomass and total above ground dry biomass than Poinsett 76. However, Market More 76 had allocated very less proportion of total above ground biomass to fruits, which resulted in lower fruit yield in Market More 76 than Poinsett 76 even though it has produced higher total above ground dry biomass. Furthermore, severe water deficit had a detrimental impact on the root growth. Root length density (RLD) and root surface area density (RSAD) decreased with decrease in amount of irrigation water. Reduction in RLD and RSAD reduces the net absorption area for water and nutrients. As a result, nutrient and water requirements of the plant were not met and plant growth decreased, which ultimately decreased the yield under severe water deficit conditions. It appeared that the total irrigation amounts applied to 80% ETc, 60% ETc and 40% ETc were not sufficient to meet the crop water requirements. So, in these irrigation treatments, plants used the stored soil water to meet the crop water requirement to some extent. As a consequence of this, soil water depletion was higher in these irrigation treatments than 100% ETc. Soil water depletion was the highest in 40% ETc followed by 60% ETc, 80% ETc, and it was the least in 100% ETc. In 60% ETc and 40% ETc, plants faced a severe stress, and they produced lower fruit yield per unit of water applied. Because of this, WUE declined in 60% ETc and 40% ETc than in 100% ETc. However, fruit yield was comparable between 100% ETc and 80% ETc, but the amount of water applied to 80% ETc was considerably lower which resulted in higher WUE in 80% ETc than in 100% ETc. Root growth and soil water depletion were not significantly different between Market More 76 and Poinsett 76. However, fruit yield was significantly higher in Poinsett 76, which caused higher WUE in Poinsett 76 than in Market More 76. These results suggested that 80% ETc irrigation level and Poinsett 76 can be recommended for successful cucumber production without causing a significant decline in fruit yield while conserving a considerable amount of water to sustain the crop production in water-limited SHP.application/pdfengSalinity stressBiocharDeficit irrigationPhysiologyGrowthWater productivityThesis2021-01-25Restricted until September 2021.