Fig. 1. The dependence of soil Cu²⁺ activity, as expressed by the -log (Cu²⁺) or pCu, on total Cu in 20Y peat soil. The solid line is fitted to pCu measurements at 5 and 9 d after Cu addition (pCu = 12.98 - 2.30 log Cu_T, r = 0.997) and the broken line is fitted to the pCu measurements at the time of maize harvest (pCu = 11.63 - 1.81 log Cu_T, r = 0.994). Total soil Cu is symbolized by Cu_T in these equations. Error bars in this and subsequent figures display ±one standard deviation unit