Variable-rate liming for the corn-soybean rotation

Abstract

<p>Precision agriculture technologies and a strip trial methodology were used to study soil sampling for pH and variable-rate liming for soybean [Glycine max (L.) Merr.] grown in a rotation with corn (Zea mays L.) in two fields. The fields included soils of the Clarion (Typic Hapludoll)-Nicollet (Aquic Hapludoll)-Webster (Typic Endoaquoll) association. Soil samples collected from 0.1-ha cells, soil survey maps, elevation and electrical conductivity maps, and aerial photos were used to simulate less intensive sampling schemes. These were 0.3- and 0.7-ha grid-point, 0.3- and 0.7-ha grid-cell, which included sampling of large cells, by soil map unit, and by management zones. Treatments were a control, a fixed lime rate, and a variable lime rate based on a 0.2-ha grid soil sampling strategy, which were replicated three times in one field and four times in the other. Crop yield was harvested with yield monitors in three years for one field and two years for the other. Soil pH across the grid points ranged from 5.4 to 8.4 (15-cm depth) in both fields. A similar pH range was observed for samples collected from eight 150-m transects with a 6-m spacing between sampling points. Most of the subsoils were calcareous. There was little or no significant crop response to lime. Yield and pH were negatively correlated in years with excessive rainfall, but positively (for corn) or not correlated (for soybean) in years with lower than average rainfall. Significantly less lime (60% less) was applied with the variable-rate method compared with the fixed-rate method. The little or no response to lime and to the variable-rate method may be explained by a usually high subsoil pH and very high small-scale pH variation. Less intensive sampling schemes identified smaller acid and alkaline areas for one field. The variable-rate method based on any of the sampling strategies considered in this study still would apply less lime than the fixed rate method in this soil association. However, the results showed no lime would be needed in soils similar to those included in this study when topsoil (0-15 cm) pH is 5.4 or higher.</p>