Comparison of soil sampling techniques for alkaline hydrolyzable‐nitrogen on clay soils

Abstract

Abstract The Nitrogen‐Soil Test for Rice (N‐STaR) provides a site‐specific N rate recommendation by quantifying alkaline hydrolyzable‐N (AH‐N). A user‐friendly method for obtaining a representative N‐STaR soil sample is needed, and this study was designed to evaluate the performance of alternative sampling techniques compared with the Dutch auger (DA). The alternative techniques included a Kleen Hole Spade dry (KHS‐D), a KHS lubricated with water (KHS‐W), a KHS lubricated with WD‐40 (KHS‐40), and the N‐STaR Bucket and Drill (BD). One soil sample was collected with each sampling technique from four blocks and was repeated across 14 sites. Each sample was analyzed for AH‐N using N‐STaR and compared against the DA. Variability in AH‐N ranged from a coefficient of variation (CV) of 4.4% at Site 3 to 22.3% at Site 5. The AH‐N at 13 of the 14 sites had no significant differences among sampling techniques. At Site 14, the AH‐N measured using the KHS‐40 was statistically higher than the DA by 25 mg AH‐N kg soil–1 and would correspond to a fertilizer N rate difference of 49 kg N ha–1. The KHS‐D probe appears to have the greatest accuracy and precision compared to the DA, although the KHS‐W, KHS‐40, and the BD produce similar results. All alternative techniques averaged a numerically higher AH‐N value than the DA but were not statistically different for 55 of the 56 observations. Therefore, these alternative soil sampling methods can be used successfully to collect soil samples for N‐STaR analysis on clayey soils.