Surface-applied lime and gypsum for improving soil chemical properties, root development, and crop yield under no-tillage in Southern Brazil

Extensive research has examined lime and gypsum application in strongly acidic no-till soils, but responses under moderate acidity remain uncertain. A 21-month field experiment was conducted in a Rhodic Hapludox under long-term no-tillage (NT) in southern Brazil. Initial soil pH ranged from 4.5 to 5.3 and exchangeable Al3+ from 0 to 0.31 cmolc dm−3 across the 0–0.60 m profile. Treatments were arranged in a randomized complete block design with four replications: untreated control, surface liming to 70% base saturation (BS70), BS70 plus the recommended gypsum rate (BS70G1), and BS70 plus twice that rate (BS70G2). Soil chemical properties were assessed at 9 and 21 months, and soybean (Glycine max), wheat (Triticum aestivum), and maize (Zea mays) nutrition, root growth, and yield were evaluated. Acidity correction advanced to 0.20 m after 21 months. BS70G2 increased Mehlich-1 P by 82% at 0–0.05 m and 154% at 0.40–0.60 m after 9 months, and by 156% at 0–0.05 m after 21 months. Gypsum increased maize root length by 59% at 0.20–0.40 m and 90% at 0.40–0.60 m. Soybean yield increased by 8.2% with lime plus gypsum, whereas wheat and maize yields were unaffected. Doubling the gypsum rate produced no additional yield benefit. Thus, surface-applied lime plus the recommended gypsum rate can improve soil chemical conditions and soybean yield under moderate acidity in no-tillage, but responses are crop-dependent and higher gypsum rates are not justified.