Copper and Zinc fractions and adsorption in sandy soil with long-term pig manure application

Copper (Cu) and zinc (Zn) fraction accumulation and adsorption capacity were evaluated in sandy-soil after 16 pig slurry (PS) and deep-litter (DL) applications under subtropical climate. Sixteen PS and DL applications to a Typic Hapludalf increased soil Cu and Zn soluble, exchangeable, mineral, organic, and total fractions. Cu mostly accumulated in organic and residual fractions (1.03, 4.39, 9.81, and 9.68, 12.9, 13.98 mg Cu kg(-1) in the control, PS, and DL, respectively), whereas Zn presented a greater increase in mineral and exchangeable fractions (0.42, 6.39, 15.46 and 1.67, 8.96, 14.83 mg Zn kg(-1) in the control, PS, and DL, respectively). Manure applications changed Cu and Zn adsorption behavior, with the greatest (895.8 mg Cu kg(-1) and 945.9 mg Zn kg(-1)) adsorption occurring in DL, which is related to the 1.5- and 1.6-times organic matter increase compared to PS and control. Cu showed a preference for soil exchangeable sites under the competitive adsorption system, reducing Zn absorption about 11 and 6 times in the PS and DL, respectively. Application of pig manure rates based solely on crop N demand is unwise as it potentiates Cu and Zn accumulation, Zn bioavailability, increasing the risk of Zn toxicity and transference to aquatic environments.