Changes in subsoil acidity with a new deep vertical lime placement practice for conservation tillage systems

Abstract

Poorly drained claypan soils in the midwestern United States that are managed for corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production often have optimum surface pH for crop growth, but are characterized by acidic subsoils. Stratification of soil acidity may inhibit root growth leading to decreased drought tolerance and grain yields. Agricultural lime application can increase soil pH and provide calcium (Ca) to the soil, but these amendments rarely affect the subsoil, especially when a conservation tillage system that results in minimal lime incorporation is utilized. The objectives of this study were to determine the effects of surface lime placement compared to a novel deep vertical lime placement practice at various rates on subsoil characteristics under corn and soybean production. Field trials were conducted from 2012 to 2016 in northeast Missouri with treatments of aglime broadcast to the surface soil or incorporated as a vertical band using a custom built shank to a depth of 51 cm (20 in) into the subsoil at 0, 3.4, and 6.7 Mg lime ha⁻¹ (0, 1.5, and 3.0 tn lime ac⁻¹). Soil pH results indicated that the top 13 cm (5 in) of soil was not affected by deep lime placement, but at depths of 13 to 25 cm (5 to 10 in) soil pH increased up to 0.6 and 0.7 units for deep vertical placed lime at 3.4 and 6.7 Mg ha⁻¹, respectively. When compared with control treatments, vertical placement of lime at 3.4 and 6.7 Mg ha⁻¹ increased subsoil pH at depths of 13 to 25 and 25 to 38 cm (10 to 15 in), respectively, one year after application. A similar comparison with the control treatment indicated that deep vertical placement at 6.7 Mg ha⁻¹ increased subsoil pH at 13 to 25 cm depths by 6.5% and 5.7% two and three years after application, respectively. Analysis of the spatial distribution of soil pH and neutralizable acidity in the soil profile indicate penetration of liming effects up to 38 cm (15 in) into the subsoil, but there was minimal evidence of movement away from the initial vertical placement band during a seven-month period.