With the assistance and cooperation of numerous private and public soil testing laboratories, the International Plant Nutrition Institute (IPNI) periodically summarizes soil test levels in North America (NA). Soil tests indicate the relative capacity of soil to provide nutrients to plants.

Therefore, this summary can be viewed as an indicator of the nutrient supplying capacity or fertility of soils in NA. This is the eleventh summary completed by IPNI or its predecessor, the Potash & Phosphate Institute (PPI), with the first summary dating back to the late 1960s (Nelson, 1980). The summary offers a snapshot view of soil test levels in 2015, but also provides a comparison to the previous three summaries which were completed in 2001, 2005, and 2010 (Potash & Phosphate Institute, 2001; 2005). Since the 2015 summary is the fourth summary in which laboratories were asked to contribute complete frequency distributions of soil test results, temporal trends in soil test level distributions can be viewed for states and provinces.

The increase in samples in this year's summary reflects the growing influence of precision agriculture in production systems. While we cannot say that the increase in samples relates directly to precision sampling schemes, the trend for more data to support precision activities supports the increase in samples submitted.

Important to appropriate use of this report is recognition that nutrient management should occur on a site-specific basis where management objectives and the needs of individual fi elds and, in many cases areas within fields, are recognized. Therefore, a general soil test summary like this one cannot refl ect the specifi c needs of individual farms. Its value lies in calling attention to broad nutrient needs, trends, and challenges, and in motivating educational and action programs that are in turn relevant to growers and their advisers.