Portable soil test laboratory results compared to standard soil test values

Abstract

Results from a commercially available portable soil test laboratory were compared to standard soil test procedures used by a public soil testing laboratory. Standard soil tests examined were water extracted NO₃‐N, pH, Acid‐P, NaHCO₃‐P, and ammonium acetate extracted K. Approximately 35 to 55 different soils were used to compare methods for each soil test. Linear regression equations between the portable laboratory soil test values and those from the standard procedures were developed. The r² values for NO₃‐N, pH, Acid‐P, NaHCO₃‐P, and K were 0.970, 0.891, 0.734, 0.742, and 0.887, respectively. The coefficient of variability values for NO₃‐N, pH, Acid‐P, NaHCO₃‐P, and K were 10, 1, 13, 15, and 6%, respectively for the portable laboratory, and 9, 2, 8, 9, and 5%, respectively for the public soil testing laboratory. Multiple regression was used to relate soil properties to soil test results. The R2 values for NO3‐N, pH, Acid‐P, NaHCO₃‐P, and K were 0.970, 0.911, 0.860, 0.940, and 0.936, respectively.

Key words:

• soil testing
• soil fertility
• extractable soil nutrients
• nitrate nitrogen
• pH
• Bray P‐l
• NaHCO₃‐P
• exchangeable potassium
• phosphorus
• soil test kit

Notes

Contribution from the Plant Science Department and the So. Dak. Agr. Exp. Sta. Project Nos. 287470 and 287454. South Dakota State Univ., Brookings, 57007 and published as Journal Paper No. 1990.

Associate Professor of Soils and Manager of SDSU Soil Testing Laboratory, Plant Science Department, South Dakota State University, Brookings, 57007.