Bell Pepper Growth Responses and Soil Environmental Changes to Humic Substances and Deficit Irrigation
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Organic matter-derived soil amendments containing humic substances (HS) play a functional role in improving plant root growth and soil quality, but their interaction with water deficit levels is unknown. In this study, lignite-derived HS were mixed with pot soil in controlled environments (growth chamber and greenhouse) and field soil in two different environmental locations (clay in Uvalde and sandy in Weslaco), then subjected to four irrigation levels -- severe deficit (20%), mild deficit (40%), moderate deficit (60%) and well-watered (80%) on bell pepper (Capsicum annuum L.) plants based on water-holding capacity in controlled environment and evapotranspiration requirement in field conditions. Plant morphology and physiology were assessed in different growth environments. Root traits, soil chemical properties and microbial activities were measured and analyzed at the end of the study. HS application significantly increased plant height and stem diameter during seedling development and early vegetative growth period, and decreased plant transpiration rates during early growth while maintaining photosynthesis at the same level as the control (increased water use efficiency), especially under severe or mild deficit levels. HS increased plant biomass accumulation in controlled environments and increased early yield in field conditions. HS increased root length, surface area and dry weight in controlled environments. These root promotion effects were consistent in field conditions although not statistically significant. HS also increased soil organic carbon as well as soil respiration and microbial population in both soil types. Plant growth iii performance was significantly decreased in severe and mild deficit stress, but was similar in moderate deficit and well-watered treatments. These results suggest that HS have the ability to ameliorate severe or mild stress in the short-term, which can reduce water loss in plants exposed transiently to water deficit conditions. In addition, this study provides evidence that the application of HS might be considered for long-term agricultural use due to their capacity to improve crop early yield, soil nutrient cycling, organic carbon retention, microbial enrichment and activity under moderate stress or well-watered conditions.
Leaf gas exchange
Qin, Kuan (2017). Bell Pepper Growth Responses and Soil Environmental Changes to Humic Substances and Deficit Irrigation. Master's thesis, Texas A & M University. Available electronically from