Evaluation of the Efficiency of Agricultural and Pelleted Lime at Increasing Soil pH and Crop Yield.

Agricultural lime (aglime) is applied to increase acidic pH to values optimum for crop production. Its effectiveness is affected mainly by the material fineness and calcium carbonate equivalent (CCE). Market availability and use of finely ground and pelleted aglime has increased in recent years, but there is limited information about its effectiveness. Six field trials were established in acidic Iowa soils (pH 4.9-6.1) with contrasting texture and organic matter. Treatments replicated three times were finely ground CaCO₃, and commercially available calcitic aglime lime and pelleted aglime broadcast which were incorporated into the soil 6 months before planting corn (Zea mays L.) at 0, 2.24, 4.48, 8.97, and 17.94 Mg CCE ha^-1. Expressing rates as effective CCE (ECCE) based on fineness efficiency factors used in Iowa changed very little the values for CaCO₃ and pelleted lime, but for aglime rates became 1.38, 2.76, 5.51, and 11.03 Mg ECCE ha^-1. Soil pH increases that were measured 5, 8, 12, 14, and 17 months after liming were statistically similar for CaCO₃ and pelleted lime for all sites and rates. On average across sites and these two sources, plateau pH was reached by the first sampling date 5 months after application (pH 5.98, 6.31, 6.70, and 6.92 for rates 2.2, 4.4, 8.8, and 17.6 Mg CCE, respectively). Soil pH increases for aglime were much smaller, and pH did not reach a plateau until 12 months after application (pH 5.75, 5.93, 6.29, and 6.63). Corn yield did not differ between sources at any site and the lowest rate maximized yield. We conclude that pelleted lime was as effective as powdered CaCO₃ at increasing pH and that fineness efficiency factors used in Iowa slightly overestimated the aglime neutralizing power, but this did not affect the yield response for the application rates and conditions of this study.