The links between potassium availability and soil exchangeable calcium, magnesium, and aluminum are mediated by lime in acidic soil

Abstract

The aims of this study were to investigate the links between potassium (K) uptake by crops and soil K, exchangeable calcium (Ca2+), magnesium (Mg2+), and aluminum (Al3+) when using lime in acidic soil in southern China. Soil samples of three treatments (chemical NP fertilizers, NPK, and NPK plus straw (NPKS)) were collected from a 26-year field experiment (0–20 cm) and then a rhizobox experiment was conducted with seven lime application rates (0–2.26 g kg−1). We investigated the soil exchangeable K+, Ca2+, Mg2+, and Al3+ and non-exchangeable K (NEK) in the rhizosphere soil (RS) and non-rhizosphere soils (NRS), and K uptake by crops. As lime addition rates increased, the average concentration of exchangeable K (EK) in RS under NPK and NPKS treatments decreased to 46.5 mg kg−1 and 70.4 mg kg−1 for maize and wheat, respectively. In treatments with lime application, the NEK concentration was higher in RS and NRS compared with the no-lime in NP treatment but was lower in RS in treatments with K fertilizer input (NPK and NPKS). The K uptake by crops under lime application significantly (p < 0.05) increased by 37.6% to 155.1% compared with the no-lime treatments. Lime application significantly increased soil exchangeable Ca2+ (42.9 to 255.7%) and decreased exchangeable Al3+ (23.7 to 86.6%). According to structural equation modeling, lime indirectly influenced K uptake by crops through its effects on soil exchangeable Ca2++Mg2+ and Al3+, EK, and NEK, which accounted for up to 39% (RS) and 46% (NRS) of the variation in the K uptake by crops. Lime directly and negatively affected EK and NEK in NRS but had no direct effects on EK and NEK in RS. Our results suggested that lime-induced K uptake by crops was mediated by K+, Ca2+, and Al3+, and that lime application resulted in higher soil K availability.