EXCHANGEABLE CATIONS AND CATION-EXCHANGE CAPACITY OF FOREST SOIL SAMPLES - EFFECTS OF DRYING, STORAGE, AND HORIZON

Concentrations of Ca, Mg, K, Na, Al, Fe, Mn, and Si extractable with 1 N ammonium chloride (NH4Cl, pH 4.5) and 1 N ammonium acetate (NH4OAc, pH 4.5) were determined for forest soil samples as follows: (1) befor e drying, and (2) at several time intervals after air-drying (1, 5, 11 and 14 wk). Values for CEC were obtained for the same samples by dete rmining (1) the sum of cations (Al3+, CA(2+), Mg2+, K+, Na+, Fe3+, and Mn2+) in the extracts [denoted CEC(Sigma cations)(NH4OAc) and CEC(Sig ma cations)(NH4Cl)], and (2) the amount of ammonium retained by the so il samples against water washing [denoted CEC(NH4OAc) and CEC (NH4Cl)] . The soils used in this investigation were taken from four New Brunsw ick upland forest sites (two sugar maple sites, one mixed wood site, a nd one spruce site). It was found that (1) extractable Mg, K, Na, and Mn levels were generally not affected by drying, storing, and type of extractant; (2) extractable Al and Fe levels increased immediately aft er drying; (3) NH4OAc-extracted Al, Fe, and Si exceeded NH4Cl-extracte d Al, Fe, and Si; (4) extracted Al and Fe levels tended to drop after 11 wk of storage; (5) small drying effects were also noticed for NH4Cl -extracted Ca; (6) CEC(NH4OAc) and CEC(NH4Cl) values decreased with in creasing time of storage; this effect was noticed most for soil sample s with high levels of organic matter (Ah, Ahe, Bm, Bf, and Bfh), and w as noticed least for soil samples taken from leached horizons (Ae) and subsoil horizons (BC and C); (7) in some cases, storage time increase d CEC(NH4OAc) in subsoils; (8) values for CEC(Sigma cations)(NH4Cl) re mained fairly independent or increased slightly with storage time, and were closely related with CEC(NH4Cl) values obtained with non-dried s amples; (9) values for CEC(Sigma cations)(NH4OAc) did not relate well with CEC(NH4OAc) and CEC(NH4Cl). Differences for extractable Al were l ikely due to Al complexation by acetate ions. Drying effects on extrac table Al and Fe (and possibly Ca) were likely due to drying-induced fr agmentation of soil organic matter. Drying and storage effects on CEC( NH4OAc) and CEC(NH4Cl) were likely due to (1) water-washing and relate d loss of organic matter, and (2) sensitivity of subsoil minerals to a ir exposure. Apparent drying and storage effects on CEC were most note d with CEC(Sigma cations)NH4OAc and were least noted with CEC(Sigma ca tions)NH4Cl.