Effects of Water Treatment Residues On Cu Transport in Surface Runoff From Citrus Groves.

Due to its wide and repeated use in agriculture and horticulture as fertilizers or fungicides copper contamination to agricultural soils has been accelerated and as well as its export potential to the adjacent surface water body. This study investigated the effects of water treatments residues (Ca-WTRs, pH 9.1, containing mainly CaCO₃ and minor CaO) on Cu concentration and loads in surface runoff water from representative citrus groves in the Indian River area, South Florida.  The concentration of Cu in soils and surface runoff water were monitored over a three-year period at two sites of Alfisol under citrus production of naval orange and grapefruit. A total of 96 soil samples, 480 surface runoff water samples were collected and analyzed for physical and chemical properties and Cu concentration.  Soil amendment with Ca-WTRs at 4 metric tons ha^-1 generally raised soil pH and Mehlich-3 extractable Ca, but decreased Mehlich -3 extractable Cu. The mean concentrations of Cu in surface runoff water was reduced by 35%  and 14% during the 2006-2009 period for the naval orange and grapefruit site,  respectively. The results from column leaching studies showed that cumulative amount of Cu in leachate after 10 leaching events was reduced by 80% for Alfisol at the 2% Ca-WTRs amendment rates, which agrees with field observation that Ca-WTRs amendment can increase Cu retention in the soils and reduce its loss into the environment. Fruit quality was to certain degree improved, and average fruit yields during the experiment period were 10 to 50% higher with Ca-WTRs application than the control, probably because Ca-WTRs amendment neutralized soil acidity and increased Ca, Mg, K availability in the soil. These results indicate that Ca-WTRs are effective in reducing Cu transport from Cu-enriched soil while it can also improve soil quality and citrus production, particularly on acidic soils.