25 Oct 2010
Soil Test Levels in North America
Soil Test Levels in North America
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 tenth summary completed by IPNI or its predecessor, the Potash & Phosphate Institute (PPI), with the first summary dating back to the late 1960s (Nelson, 1980).
UPDATE Bulletin on Soil Test Levels in North America, 2010 is Now Available
This publication offers a snapshot view of soil test levels in the U.S. and Canada in 2010, but also provides a comparison to the previous two summaries which were completed in 2001 and 2005. Since the 2010 summary is the third in which laboratories were asked to contribute complete frequency distributions of soil test results, temporal changes in soil test level distributions can also be viewed for the second time for states and provinces.
The bulletin is available in print, or in pdf format via CD, or both.
Preview of 2010 Soil Test Summary
The 2010 International Plant Nutrition Institute (IPNI) summary of 4.5 million soil samples is probably the most comprehensive evaluation of soil fertility ever conducted in North America.
The 2010 summary includes results of tests performed by 60 private and public laboratories on soil samples collected in the fall of 2009 and spring of 2010. Great appreciation is extended to all the labs cooperating. Their assistance has resulted in the largest summary of soil samples ever conducted in the U.S. and Canada. Submissions from laboratories indicate that use of soil testing has increased substantially since 2005. The 2010 summary gives a more complete evaluation of the components of soil fertility than previous summaries, providing information about phosphorus (P), potassium (K), sulfur (S), magnesium (Mg), zinc (Zn), chloride (Cl-), and pH.
Introduction to changes in soil P and K since 2005
Soil P - The 2010 summary indicates the median P level (50% of samples are above and below this level) for NA for the 2010 crop was 25 ppm, a 6 ppm decline from 2005. Phosphorus levels vary markedly among states and provinces with the northern Great Plains generally having the lowest P levels as has been the case in past summaries. However, unlike much of the rest of the intensively cropped regions of the country, this region tended to show increases in soil P or at least no declines from the 2005 summary.
Soil K - The median K level for NA for the 2010 crop was 150 ppm, a 4 ppm decline from 2005. Median K levels in many states east of the Mississippi River and in the provinces of eastern Canada are at or below agronomic critical levels, indicating that 50% or more of the sampled areas represented likely require annual K application to avoid yield losses. The higher K levels in the West reflect the less weathered status of western soils. However, along the western Corn Belt and much of the Great Plains, crop removal far in excess of K additions are consistent with the declines in soil tests observed from 2005 to 2010. Many areas in the Northeast also experienced significant K declines.
Critical Soil Test P and K Maps for 2010
Soil Test Levels in North America 2005
Nelson, W.L. 1980. Better Crops 63(4): 6-10.