Corn and soybean response to soil pH level and liming
Limestone application to raise soil pH is needed when the pH is too acidic to allow for optimum crop growth and yield. Some Iowa soils are naturally acidic, and others become acidic over time mainly due to sustained N application for corn with urea or ammonium-based products that acidify soils during the microbial transformation of ammonium to nitrate (nitrification). Soil pH decreases as the acidity increases because the pH measurement expresses acidity as the negative logarithm of H+ ion concentration. Alfalfa is the most sensitive crop to low pH grown in Iowa, while forage grasses are the least sensitive and corn and soybean are intermediate. Soil acidity can affect plant growth directly or indirectly by affecting the plant-availability of several nutrients, increasing levels of some elements to phytotoxic concentrations, and influencing microbial activity or other soil properties.