Northeast Region Certified Crop Adviser (NRCCA) Study Resources

In This Section

• Introduction
• PO 15 Fertilizer analysis conversions
• PO 16 Soil sampling
• PO 17 Variability in soil test results
• PO 18 Fertilizer recommendations
• PO 19 Soil test interpretation
• PO 20 Soil sampling strategies
• PO 21 Pre-sidedress nitrogen test
• PO 22 Plant tissue analysis
• PO 23 Plant nutrient level
• Summary

Competency Area 3: Soil Testing and Plant Tissue Analysis

PO 23. Recognize how the following terms relate to plant nutrient level.

1. Critical value or range.
2. Sufficiency range.
3. Optimum, below optimum, and above optimum soil nutrient levels.
4. Luxury consumption.
5. Toxicity level.

Critical value or range indicates the soil or tissue content below which the plant most likely is deficient in that specific nutrient and production could be enhanced by addition of the nutrient. Below that critical value, the nutrient levels are below optimum. The sufficiency range is the nutrient level at which the plant has enough nutrients to function and develop properly, but not so much that it is poisoned. This is reported as "medium" or "high" on soil tests. Optimum, below optimum, and above optimum soil nutrient levels are terms used to describe whether plants have sufficient nutrients. If soil test levels are below the critical agronomic value, the test will come back as below optimum; if soil test levels are above the critical agronomic value, the test will come back as above optimum.

Luxury consumption occurs when soil nutrient levels are above optimum and plants take up more of a nutrient than needed for functioning and production. Potassium (K) is commonly taken up in excess.

The toxicity level is the nutrient level at which there is so much of a nutrient that it can harm the plants. This value will be reported as either a "high" or "very high" level on a soil test.

Corn plants exhibiting symptoms of low (left), adequate (middle), and excessive (right) nitrogen.