Effect of Compost Amendment on Heavy Metals, Nitrogen and Phosphorus in a Peat-Based Container Medium

A laboratory study was conducted to evaluate the effect of compost amendment on mobility and leaching potential of heavy metals, nitrogen （N） and phosphorus （P） from a peat-based commercial container medium containing 700 g kg^-1 peat, 200 g kg^-1 perlite and 100 g kg^-1 vermiculite at varying amendment rates of compost （0, 0.25, 0.50, 0.75 and 1.00 L L^-1）. Increasing compost amendment significantly and linearly increased the pH （P 〈 0.01）, the total concentrations of organic carbon （P 〈 0.05）, copper （Cu） （P 〈 0.01）, cadmium （ca） （P 〈 0.01）, and lead （Pb） （P 〈 0.01）, and increased the bulk density （P 〈 0.01） of the medium. The electrical conductivity （EC）, and total N and P of the medium increased significantly （P 〈 0.01） and quadratically with increasing compost amendment. The relationship of the C/N ratio of the medium with the compost amendment rate was decreasing, significant （P 〈 0.01） and cubic, while that of the total Zn was increasing, significant （P 〈 0.01） and cubic. Extractable P, NO3-N, and NH4-N increased initially with an increasing compost amendment of up to 0.50 L L^-1 and then decreased with further increasing compost rate. Increasing compost rates resulted in a highly significant （P 〈 0.01） and linear increase in total Cd, Cu, and Pb, and a highly significant （P 〈 0.01） and cubic increase in total Zn in the medium. Increasing compost rates also significantly （P 〈 0.01） increased extractable Cu （linearly） and Zn （quadratically）, but significantly （P 〈 0.01） decreased extractable Pb （linearly）. There was no significant effect of compost amendment on the extractable Cd concentration in the medium. However, with increasing compost rates from 0.25 to 1.00 L L^-1, extractability of P, Cd, Cu, Pb and Zn （extractable concentration as a percent of total） was decreased, indicating that compost amendment could lower the leachability of these elements from the medium.

Extractability and Mobility of Copper and Zinc Accumulated in Sandy Soils

Extractability and mobility of Cu and Zn and their relationships with 1) accumulation of Cu and Zn and 2) soil pH were studied in three sandy soils (Wabasso, Ankona, and Winder) from commercial citrus groves in Florida, USA. The soils, with a broad range of Cu and Zn concentrations, were fractionated by a modified procedure of Amacher, while Cu and Zn mobility were evaluated using column leaching. The extractability of Cu and Zn increased with decreasing soil pH. Also with increasing total soil Cu and Zn for extractable Cu in the Wabasso sand a threshold level, where the metal extraction rate increased, was noted at 100 mg kg-1, whereas for extractable Zn in the Wabasso sand the threshold level was found at 60 mg kg-1 and in the Ankona sand at 120 mg kg-1. These results suggested that the release potential of Cu and Zn was greater in the Wabasso sand than in the Ankona sand. The column leaching experiment showed that at total soil Cu or Zn concentrations < 100 mg kg-1 all leachates had low Cu and Zn concentrations. However at total concentrations > 200 mg kg-1 for Cu and > 150 mg kg-1 for Zn with decreasing soil pH, the concentrations of both Cu and Zn in the leachates increased exponentially. Also in these sandy soils soluble Cu and Zn mainly originated from the exchangeable fractions, and pH was a key factor controlling Cu and Zn extractability and mobility.