When should pre-sidedress soil nitrate testing (PSNT) for corn be conducted?

Pre-sidedress soil nitrate testing (PSNT) for corn should be conducted when the corn is approximately 12 inches tall because this timing aligns with the critical growth phase when the corn plant’s nutrient needs begin to increase significantly.

At this height, the plants are typically well-established, and the roots are actively taking up nutrients from the soil. Testing at this stage allows for an accurate assessment of the soil's nitrate levels, helping to determine if additional nitrogen fertilization is necessary to prevent nutrient deficiency during the critical period of biomass accumulation.

Conducting the test a bit earlier, for instance, when the corn is 6 inches tall, might not provide a reliable indication of the soil's nutrient status as the roots may still be developing and the uptake of nitrogen may not yet be optimal. Similarly, testing after the corn has reached physical maturity, like when it has started to tassel or is 18 inches tall, would be too late to adjust nitrogen applications effectively. At this point, the decision-making process would be limited since critical growth stages translating to yield potential may have already passed.