Improving crop production with higher resource use efficiency and mitigating plant growth in abiotic stress scenarios are among the main targets for sustainable agriculture. Humic substances (HS), a type of plant biostimulants, have been widely tested for their bio-active effects on plant growth. However, despite the commonly used liquid HS products with foliar spray or solution injection, solid HS products used as media or soil amendments were less reported. In this dissertation, lignite-derived solid HS were tested for their application in vegetable production, including applied use on nursery seedling growth and field crop production. Their mode of action on mitigating plant responses under abiotic stresses was also illustrated. In the seedling study, growth media amended with 1% (v/v) HS showed beneficial effects on seedlings shoot and root development for tomato, pepper, watermelon, and lettuce. Stronger transplant quality ultimately translated into higher productivity. In the field production study, soil amended with HS (5 t/ha) showed a significant increase in soil organic carbon content, which was found to be positively correlated with crop water use efficiency. HS application also increased watermelon early yield by 38.6% and total yield by 11.8%, with the improvement more significant under deficit irrigation. When soil was amended with a lower rate of HS (1.5 t/ha), tomaot leaf growth and shoot biomass were increased during early growth, while total nitrogen accumulation and nitrogen use efficiency were enhanced during late growth, with portion of the improvements achieved under low nitrogen input. In addition, HS application increased tomato yield by 28.4% in the first year, and 7.5% in the second year. HS amendments also altered the soil micro-environment, which resulted in higher beneficial bacterial and fungal communities, especially under N stress conditions. HS application improved plant defense under stress conditions by increasing water and nutrient uptake, reducing water loss, and maintaining water potential and nitrogen status, which resulted in less cell damage. These results showed that lignite-derived HS possessed great potentials to use as soil or media amendments in vegetable production systems to improve plant growth and resource use efficiency, with additional mitigating effects for stresses.
