Soil pH and Crop Grain Yield as Affected by the Source and Rate of Lime

Uncertainty exists concerning soil pH change and crop yield after applying different lime sources and rates. The objective of this study was to evaluate effects of different lime sources on soil pH and crop responses. Four trials were established on Iowa soils with pH 5.39 to 5.71. Pure CaCO3 and calcitic (2.3 g kg−1 Mg) or dolomitic (80.7 g kg−1 Mg) limestones were incorporated into the soil in spring 2009 at 0, 4.5, 9, 13.5, or 22.4 Mg ha−1 calcium carbonate equivalent (CCE). Soybean [Glycine max (L.) Merr.] was planted in 2009 and corn (Zea mays L.) in 2010. After liming we measured soil pH (15-cm depth) seven times for 16 mo, subsoil pH (15–30 cm) after 1 yr, and grain yield. On average, maximum pH was reached 86, 136, and 129 d after liming for CaCO3 and calcitic or dolomitic limestones, respectively. Maximum pH was reached earlier than usually assumed for similar conditions. Maximum pH with CaCO3 always was higher than with dolomitic limestone and sometimes higher than with calcitic limestone. Maximum pH with calcitic limestone was higher than with dolomitic limestone for at least two rates at all sites, which was explained by the dolomitic limestone coarser particle size and higher Mg content. Only the highest rate of all sources increased subsoil pH at one site. Liming increased yield of both crops in two sites but the sources did not differ. Differences among lime sources effects on soil pH did not affect the crop yield response to lime.