Variability of Soil Analysis in Commercial Laboratories: Implications for Lime and Fertilizer Recommendations

Abstract

Data of soil analysis of 20 samples of 84 commercial laboratories were used to estimate discrepancies among results and analyze the implications for fertilizer recommendations. More than 90% of the laboratories had all results of basic routine analysis of individual samples within the confidence interval (CI). Laboratories with the best performance in the proficiency test (grade A) had only 2.9 and 4.0% of the results outside the CI for the basic and the micronutrient set, respectively. However, the corresponding figures for grade C and D laboratories were 26.2% (basic) and 20.7% (micronutrients). Lime recommendation for a soil with 32% of soil base saturation reached the target value of 70±8% in 74% of the cases. In about 90% of the cases, fertilizer recommendations were on or close to the target rates Sizeable deviations of the fertilizer recommendations for P and K that could affect profit occurred in less than 5% of the results reported.

Keywords:

• Quality control
• soil proficiency test
• soil testing