2.4. Analytical Methods
The plant samples were dried and weighed. After weighing the three replicates of each compartment from each plot were bulked together to give one composite sample of each compartment per plot, thus resulting in three replicate composite samples per treatment. The organic layer samples of the soil cores were dried and milled to pass through a 1 mm sieve, and thereafter they were divided into two parts for the total and exchangeable analysis. Total Cu and Ni concentrations from the organic soil and plant samples were determined, following microwave assisted wet digestion in HNO3 and H2O2, by Inductively Coupled Plasma Atomic Emission Spec-trometry (ICP-AES).
Exchangeable Cu and Ni were determined by extraction with 0.1 M BaCl2 + 2% EDTA, (7.5 g of mulch or 15 g of mineral soil/150 ml extractant, shaking for 2 hours) followed by filtration and analysis by ICP-AES.