Soil chemical properties and crop response to gypsum and limestone on a coarse-textured Ultisol under no-till in the Brazilian Pampa biome

Abstract

The primary aim of this work was to assess the effect of rates of gypsum used alone and in combination with limestone on (a) soil nutrient contents and acidity, and (b) soybean and maize yields, on a subtropical coarse-textured Ultisol with a low cation exchange capacity (CEC) under no-tillage (NT). For this purpose, a field experiment using different rates of gypsum (0.0, 0.5, 1.0, 2.0 and 4.0 Mg ha−1) with or without limestone at 2.0 Mg ha−1 was started in August 2013. The experimental design was completely randomized blocks with three replications. The soil was sampled in five different layers (0–5, 5–10, 10–20, 20–40 and 40–60 cm) after 52 months, and crop yield was assessed in the seasons 2014/2015 and 2016/2017 for maize, and 2015/2016 and 2017/2018 for soybean. Surface application of limestone increased soil pH and base saturation in the 0–10 cm soil layer without exceeding the critical levels or having a significant effect on crop yield. Gypsum only altered the concentration of exchangeable Mg2+ in the soil, which decreased with increasing Ca2+/Mg2+ ratio in the subsurface layers as the amendment rate was increased. As a result, gypsum reduced maize yield in the first harvest after application, possibly by making the soil deficient in Mg2+, and the negative effects on microbial biomass. No similar effect was observed in the subsequent years. Applying gypsum to soils with low CEC and acidity in the subsurface layers not only fails to increase crop yield but also may induce Mg deficiency.