Nitrogen is the most elusive nutrient to manage and, when deficient, will significantly limit yield potential to a point that profits are lost. Having the right amount of nitrogen available at the right time is essential to achieving profitability.
A corn plant uses around 10% of the nitrogen it needs during the first three weeks of growth. Then, during the next five weeks (V4 to V18), it needs to take up 65% of its total seasonal nitrogen requirement. If nitrogen supply is limited during this period, yield and profits will suffer. Taking a pre-sidedress nitrate test (PSNT) at the V4-V5 stage indicates how much nitrogen is available in the soil from cover crops, legumes, applied manure and other organic sources.
Timing is very important; samples should be taken five to ten days before sidedressing to allow time to collect the sample, have it analyzed and receive the results. Samples taken too early will not be as accurate because nitrogen is continually released (mineralized) in the spring as the soil warms.
A&L Great Lakes analyzes PSNT samples and reports results the next business day after receipt. PSNT soil samples should represent no more than 20 acres. The sampled area should be consistent for past crop, soil types and manure applications. Sample the soil 12 inches deep, taking 15 to 20 cores per field. Avoid probing through the starter band. If fields have significantly differing soil types or drainage patterns, sample these areas separately. In addition, it is generally not recommended that these samples be analyzed as a part of a basic soil test, because of the differences in recommended sampling depth.
More information on the PSNT, including information on sampling and sample handling, is outlined in our PSNT Fact Sheet, which is available from our website.