The 2010 IPNI soil test report highlights changes in Michigan soil nutrient levels

The median P level of Michigan soils declined by 7 ppm and median K level declined by 18 ppm in 2010 compared to 2005. The soil pH change was minor. There was a substantial increase in the number of soil tests performed.

The International Plant Nutrition Institute (IPNI) has released the 2010 report of soil tests in North America. Approximately 4.4 million samples from 63 university and private laboratories were included. Soil tests indicate the relative capacity of soil to provide nutrients to plants. The Michigan data for median phosphorus (P) and potassium (K) and soil pH is summarized in Table 1.

Table 1. The median soil P and K and pH levels in Michigan.

Year * Bray P1 (ppm) K (ppm) Soil pH
2001 50 128 6.5
2005 49 149 6.6
2010 42 131 6.7

* The data is based on approximately 67,927 samples in 2001;
98,297 in 2005; and 198,915 in 2010.

The median P levels declined by 7 ppm in 2010 compared to 2005. Since soil P levels are highly buffered, this decline is slow but significant. The median K declined by 18 ppm. To some extent, these declines reflect crop removal rates in excess of P and K additions. Soil pH change was minor. This report, Soil Test Levels in North America 2010, is available at the IPNI website.

This report also shows the frequency distributions of soil magnesium (Mg), sulfur (S), zinc (Zn) and chloride (Cl) levels. Of particular interest was the increase in frequency of soils testing low for S which is consistent with reports of increasing S deficiency in crops. Most scientists do not consider soil tests for S to be of good diagnostic value, rather tissue tests are preferred.

There was a substantial increase in soil tests in 2010 compared to 2005. In the Corn Belt region, the number of soil tests represented about a 50 percent increase. It is encouraging that agricultural producers are increasingly relying on soil testing as a guide to nutrient management decisions. Most university fertilizer recommendations are based on agronomic, economic and environmental considerations.

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