Soil Test Categories Have Changed to Probability of Response

The rating based on probability of response will be specific to each crop (or group of crops), because there are differences in the way these crops respond to added fertilizer. For soil test reports where the crop to be grown has been indicated, the response category shown in Table 1 will be displayed on the report beside the numeric value for the soil test.

Response to added fertilizer is not exactly the same in each field or each year. As a general rule, with low soil tests the crop will usually respond to added fertilizer, and the difference between the fertilized and unfertilized yields will be large. As the soil test values increase, the probability of a profitable response to fertilizer declines, as does the size of the expected yield or quality response. In the Low Response category, most crop responses would be improvement to the early growth of the crop from a starter effect. Fertilizer application to soils in the Rare Response category may cause an improvement in early growth, but is more commonly done to replace nutrients removed by the crop, or to provide nutrients to pockets within variable fields that are lower in fertility. Any yield response is unlikely to be large enough to pay for the added fertilizer.

The No or Negative Response (NR) rating signifies that application of this nutrient in fertilizer or manure may lower crop yield or quality. Phosphate additions to these soils can induce zinc deficiency on soils low in zinc and can increase the risk of water pollution. Potash additions may induce magnesium deficiency on soils low in magnesium. 

More information on Soil Test Categories refer to the OMAFRA website.

Related Links:

• OMARFA Soil Test Categories

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