Precision of commercial soil testing practice for phosphorus fertilizer recommendations in Finland

Authors

• T. PELTOVUORI

DOI: https://doi.org/10.23986/afsci.5631

Abstract

Implementation of the Agri-Environmental Program in 1995 has emphasized the role of advisory soil testing in phosphorus (P) input planning and markedly expanded the market for commercial soil testing in Finland. A small precision experiment (5 laboratories) and a simulation study on soil sampling were conducted to evaluate the current precision of the soil testing practice for P. The observed values of reproducibility (95% probability) of soil P determination were 42-61% of the mean P concentration for three soils. This approximately corresponds to a maximum error of one P class in a seven-step classification system. Soil texture and organic matter content are used as secondary variables in P fertilization planning. In commercial soil testing these are both determined by finger assessment and the results have significant errors in most laboratories. Erroneous texture determinations are more likely to lead to errors in P fertilizer recommendations than soil P analysis itself. In this study the largest deviation from a correct P fertilization recommendation was +10 kg ha-1. In soil sampling simulation, stratified random sampling in areas of differing texture gave the most consistent results with geostatistical analysis of the soil test data, as compared with random, systematic, and judgment sampling strategies.;