Effects of long-term N fertilizer-induced acidification and liming on micronutrients in soil and in bromegrass hay

Abstract

A field experiment was initiated in 1968 at Crossfield, Alberta to determine the effects of 27 years of fertilization with ammonium nitrate (0, 56, 112, 168, 224, and 336 kg N ha −1 yr −1) to bromegrass ( Bromus inermis L.) on soil acidification, and on micronutrient concentrations in soil and in hay. A portion of each N plot was treated with surface-applied finely-ground calcium carbonate (referred to as lime) in 1991 at rates to bring soil pH (in H 20) near 7.0, and both the limed and non-limed portions were sampled for soil and hay in the autumn of 1994. Soil pH was 6.85 in the 0–5 cm layer when no N was applied, but pH values were markedly reduced with increasing N rates, with pH 4.10 or less when N rate was 168 kg N ha −1 or more. There was also a drastic depression in soil pH from N application in the 5–10 cm layer. In the 10–15 cm soil layer, pH decreased only at the highest N rate (336 kg N ha −1). Liming increased markedly soil pH in the 0–5 cm layer. The increase of CaCl 2–extractable Al and DTPA–extractable Fe in soil was closely correlated with the decrease in soil pH from N fertilization. Liming decreased extractable Al in soil in the 0–5 and 5–10 cm layers, while increasing extractable Fe in the 0–5 cm and decreasing it in the 5–10 and 10–15 cm layer. In the 0–5 cm soil layer, DTPA–extractable Mn first increased with N application at 112 kg N ha −1 and then decreased sharply beyond that N rate. In the 5–10 cm layer, extractable Mn increased at 168 and 224 kg N ha −1 rates, while in the 10–15 cm layer it maximized at the 336 kg N ha −1 rate. Liming had no effect on extractable Mn in the 0–5 cm soil layer, but it decreased Mn in the 5–10 and 10–15 cm layers. There was little or no effect of N fertilization and liming on extractable Zn and Cu in soil. The bromegrass hay yielded more as the rate of N was increased up to 224 kg N ha −1, but yield then decreased with the highest N rate (336 kg N ha −1). Liming increased hay yield, but only in the third and fourth year after liming and then only on those treatments which had received 168 kg N ha −1 or more. The concentration of Fe and Al in hay decreased with N application, but concentration of Zn and Mn in hay increased. There was little effect of N fertilizer on Cu. Liming decreased the concentration of Fe, Al, and Mn in forage, but it had little effect on Cu and no effect on Zn.