Quality Control in Soil Testing using the Internal Standards: Temporal Variability in Organic Carbon and Extractable Nutrient Elements

Internal soil standards are used in an analytical laboratory as one of the tools for providing feedback on the quality of soil-testing service provided. The objective of this study is to provide results on the temporal variability in soil-test values of the internal soil standards used for soil organic carbon and extractable phosphorus (P), potassium, sulfur, boron, and zinc determination in our analytical service laboratory. The range, mean, standard deviation, and coefficient of variation values for the internal standards for various fertility parameters varied according to the parameter and were generally of acceptable quality, except for the extractable P (Olsen P) in the lower range of extractable P. Our results show that the use of internal soil standards in an analytical service laboratory is a simple, inexpensive, and effective tool for providing feedback on the quality of soil-testing service.