Soil-sampling alternatives and variable-rate liming for a soybean-corn rotation

Precision agriculture technologies can be used to manage soil pH. This study compared soil-sampling schemes for pH and evaluated variable-rate (VR) liming for soybean [Glycine max (L.) Merr.] and corn (Zea mays L.). Global positioning systems and yield monitors were used in two fields. Soils were Typic Hapludolls, Aquic Hapludolls, and Typic Endoaquolls. Treatments were a control and a fixed-rate (FR) or VR liming based on a 0.2-ha soil-sampling scheme. Soil pH (15-cm depth) ranged from 5.4 to 8.4, and most subsoils were calcareous. Treatments were applied before soybean to long and replicated strips. Grain yield and soil pH were measured during 3 yr in one field and 2 yr in the other. Initial pH; canopy photos; and soil survey, elevation, and electrical-conductivity maps were used to simulate sampling schemes based on larger cells or zones. Liming increased (P less than or equal to 0.05) corn yield in one site-year (230 kg ha(-1)), and liming methods did not differ. The VR method applied less lime (56-61%) and reduced PH variability in one field. The lack of response was explained by high subsoil pH and high small-scale variation of topsoil pH. Sampling schemes based on 0.7-ha cells or zones identified smaller acid and alkaline areas than schemes based on small cells. Results suggest that yield response from lime is not likely when calcareous subsoils are present and topsoil pH is as low as 5.5. A VR liming method would apply less lime than a FR method in soils similar to those in this study.