Impacts of calcium water treatment residue on the soil-water-plant system in citrus production

Long-term use of copper (Cu) based fungicides has accelerated Cu contamination in soils and subsequently its export to the environment. Field trials were conducted in representative commercial citrus groves in the Indian River area, South Florida to evaluate the effectiveness of calcium water treatment residue (Ca-WTR) for stabilizing Cu in soil and its subsequent influence on Cu loading in surface runoff and citrus growth. Soil and surface runoff samples were monitored over a 3-year period on two field sites under navel orange and Ruby Red grapefruit production. Soil amendment with Ca-WTR generally raised soil pH and soil available Ca, but decreased available Cu. The mean concentrations of Cu in surface runoff water were reduced by 36 % and 28 % for the navel orange and grapefruit site, respectively. The results of species distribution of Cu in the runoff water using MINTEQ indicated that the application of Ca-WTR decreased the concentrations of free Cu2+ by 61 % and 39 % for the two sites. Fruit quality and yields were improved, because of the improved nutrient availability and other soil conditions. The results indicate that in situ application of Ca-WTR may provide a cost-effective remediation method for the Cu-contaminated soils without affecting citrus production.