Comparison of Soil Sampling Methods for Site-Specific N Rates on Clay Soils Using N-Star.

Development of N-STaR (Nitrogen Soil Test for Rice) provides field-specific N recommendations for Arkansas rice production on both silt loam and clay soils. Currently, a modified bucket and drill are used to obtain samples for rice produced on silt loams, but an alternative method is being sought for clay soils. Field-specific N rates for clay soils is highly dependent on the accurate collection of a 0-30 cm soil sample, and a more convenient and reproducible soil sampling method is desired. Comparison of five sampling methods including a Dutch Auger (DA), N-STaR Bucket and Kleen Hole Spade (KHS) with three lubrication methods was completed across a range of clay soils in Arkansas to determine if there is a viable alternative to the N-STaR Bucket currently used for silt loam soils. Four sample cores were collected using each of the five methods at eight locations, analyzed using the N-STaR soil analysis procedure and a simple ANOVA was used to compare sampling methods within a site. No significant difference (α=0.05) was found between methods at six of the eight sites. Soil samples taken using the KHS probe lubricated with WD-40 were significantly different between samples taken with the DA at site 8. At site 3, there was a significant difference between the samples taken with the dry KHS probe and wet KHS compared to the DA. The KHS lubricated with water was the most precise method at four of the eight sites, but not the most accurate. The N-STaR bucket was the most accurate of the methods at five of the sites when compared to the DA and may be the best technique for N-STaR samples on clay soils. Although this data indicates the potential for alternative sampling methods, the error associated with a given method will ultimately determine its suitability for implementation.