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library:articles:why_labs_have_different_soil_test_results 2010/02/23 14:25 library:articles:why_labs_have_different_soil_test_results 2010/03/30 16:40 current
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  - Bray & Kurtz P1 (The original "standard" extractant, developed for acid Midwest soils)   - Bray & Kurtz P1 (The original "standard" extractant, developed for acid Midwest soils)
  - Bray & Kurtz P2 (A stronger version of P1 that identifies less soluble P, due to rock-phosphate use)   - Bray & Kurtz P2 (A stronger version of P1 that identifies less soluble P, due to rock-phosphate use)
-  - Olsen (Developed for high pH soils, where the Bray & Kurtz methods were thought to be weak)+  - Olsen (Developed for high pH soils, where the Bray & Kurtz methods were thought to be weak)
  - Morgan (Developed in the Northeast States as a more "universal" extractant for acid soil)   - Morgan (Developed in the Northeast States as a more "universal" extractant for acid soil)
  - Modified Morgan (An improvement, to include micronutrient analysis)   - Modified Morgan (An improvement, to include micronutrient analysis)
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A common problem in understanding soil test reports is in understanding the relationship between the different units of measure that labs use in reporting results (item 3, above). The following is a list of the common reporting units and the factors that can be used to convert them. A common problem in understanding soil test reports is in understanding the relationship between the different units of measure that labs use in reporting results (item 3, above). The following is a list of the common reporting units and the factors that can be used to convert them.
-  * Parts per million (ppm) * 2 = Pounds per acre (lb./a+  * Parts per million (ppm) × 2 = Pounds per acre (lb./ac
-  * Lb./a of P * 2.291 = lb./a of P<sub>2</sub>O<sub>5</sub> or lb./a of P<sub>2</sub>O<sub>5</sub> 0.4364 = lb./a +  * Lb./ac of P × 2.291 = lb./ac of P<sub>2</sub>O<sub>5</sub> or lb./ac of P<sub>2</sub>O<sub>5</sub> × 0.4364 = lb./ac
-  * Lb./a of K * 1.2046 = lb./a of K<sub>2</sub>O or lb./a of K<sub>2</sub>0 0.8302 = lb./a of K+  * Lb./ac of K × 1.2046 = lb./ac of K<sub>2</sub>O or lb./ac of K<sub>2</sub>0 × 0.8302 = lb./ac of K
Another common practice is to report results as an "index". Labs sometimes do this in an effort to improve the relationship of the soil test to the availability of the nutrient to the plant. Most people in agriculture understand that there are many factors that affect the availability of nutrients to the crop. These factors are in addition to the amount that is measured by the soil test. When the agronomists at a lab believe that they have discovered a way to include some of these other factors, they develop formulas that modify the analytical result. These modified results appear on the soil test report as an index, and are normally labeled as such. There is nothing wrong with using an index system, if it improves the relationship between the soil test and the crop response. Since an index is unique to the lab that developed it, it is often difficult to correlate with another lab's results. With all of these complications, the analytical side of a soil testing service is still typically more accurate and precise than recommendations. With nutrient management planning there are also some states that are indexing the phosphorus number. Most of these index numbers have been developed as a compromise between environmental agencies which deal with water quality issues, NRCS specialists and state land grant university agronomists. Another common practice is to report results as an "index". Labs sometimes do this in an effort to improve the relationship of the soil test to the availability of the nutrient to the plant. Most people in agriculture understand that there are many factors that affect the availability of nutrients to the crop. These factors are in addition to the amount that is measured by the soil test. When the agronomists at a lab believe that they have discovered a way to include some of these other factors, they develop formulas that modify the analytical result. These modified results appear on the soil test report as an index, and are normally labeled as such. There is nothing wrong with using an index system, if it improves the relationship between the soil test and the crop response. Since an index is unique to the lab that developed it, it is often difficult to correlate with another lab's results. With all of these complications, the analytical side of a soil testing service is still typically more accurate and precise than recommendations. With nutrient management planning there are also some states that are indexing the phosphorus number. Most of these index numbers have been developed as a compromise between environmental agencies which deal with water quality issues, NRCS specialists and state land grant university agronomists.
 
library/articles/why_labs_have_different_soil_test_results.txt · Last modified: 2010/03/30 16:40 by bill