Christoph Kessel, Nutrition (Horticulture) – Program Lead
From HortMatters, Vol. 13, Issue 4
A soil test report provides a rating for the reported nutrient levels. Those are the little letters beside the numbers in the columns; the L (low) and H (high) or it may be HR (high response) and NR (no response).
Don’t ignore these little letters; even before looking at the report’s recommendations, they provide a guide as to whether or not the crop will benefit from any additional fertilizer.
These ratings depend on two things. The first one is the nutrient’s concentration in the soil determined by the laboratory. This reported value is an estimate of the plant available nutrient and is usually reported in ppm (parts per million). The second is the crop being grown.
For example: a soil test phosphorus of 28 ppm would be ranked as very high (VH) or rare response (RR) for sweet corn but only medium (M) or medium response (MR) for broccoli. At this phosphorus test level OMAF and MRA guidelines would be 20 kg P2O5/ha for sweet corn and 140 for broccoli.
While the rating letters used may differ between laboratory reports, the concept is the same: for nutrient test values ranked as very high or excessive, or listed as rare or no response categories, it is unlikely that the crop will respond to any added fertilizer.
This can mean a lot to a fertilizer budget. The dollars spent on fertilizers for nutrients ranked very high or excessive, or rare or no response will probably not gain any more in yield or quality.
More information on soil test ratings can be found at: http://www.omafra.gov.on.ca/english/crops/facts/fert-rec-tables-toc.htm.