ZINC AND COPPER PLANT UPTAKE IN SOILS AMENDED WITH FEEDLOT MANURE OR SOLUBLE SALTS
In agriculture, inorganic and organic amendments were used to improve soil properties but those can highly modify de bioavailability of metals in the soil environment and plant uptake. In a field micro-plot trial, we compared the effect of organic fertilization (feedlot cattle manure) versus conventional inorganic fertilizers (CuSO4-ZnSO4) on copper (Cu) and zinc (Zn) plant composition. At first harvest (30 d), the Cu concentration in aerial biomass was higher (P < 0.05) in plots receiving feedlot manure compared to the control tests. Fertilization with soluble salts did not increase Cu concentration in forages samples. For Zn, the results showed a positive response for all fertilization treatments (P = 0.0148), but better outcomes were obtained for organic amendments. At the second harvest (90 d), Cu and Zn concentrations in leaf biomass showed minimum differences after different type of fertilization compared to the control (P > 0.05). These results indicate a more positive response of feedlot manure in comparison with inorganic fertilizers at first harvest. At 90 d, independently of the fertilization treatment, the Cu and Zn concentrations in aerial plant biomass decreased compared to 30 d. The study shows that at long harvest time, a second fertilization should be considered to prevent a depletion of metal concentration bellows beef cattle requirements established by National Research Council (NRC).