By Blake Jackson
After several years of excessive rainfall during the growing season, many corn producers have recognized the value of delaying a large portion of their nitrogen (N) fertilizer applications until sidedressing.
According to Penn State Extension soil fertility specialist Charles White, this strategy can significantly reduce the risk of early-season nitrogen losses.
As mid-June approaches, growers who split-applied nitrogen should begin evaluating how much additional N their corn crop may need. Several in-season tools can help assess nitrogen availability and guide sidedress decisions.
Two commonly used methods are the Pre-Sidedress Soil Nitrate Test (PSNT) and the chlorophyll meter test. Both are designed to estimate nitrogen supplied through the mineralization of soil organic matter.
These tools are particularly useful in fields with a history of manure applications or rotations involving legume crops, where natural nitrogen release can reduce fertilizer requirements.
The PSNT involves collecting soil samples from the top 12 inches when corn reaches about 12 inches in height, typically around the V5 growth stage.
The nitrate concentration measured in the sample helps estimate current and future nitrogen availability from soil organic matter.
Proper sample handling is critical. Samples should be dried promptly or refrigerated to prevent additional nitrogen transformations before laboratory analysis.
Producers should also avoid sampling immediately after heavy rainfall, as nitrate may temporarily move below the sampling depth.
The chlorophyll meter test offers another approach by measuring the greenness of corn leaves, which reflects nitrogen status. This method is most effective when very little nitrogen has been applied at planting.
Higher chlorophyll readings generally indicate greater nitrogen availability from the soil, allowing producers to reduce sidedress rates.
For fields where substantial nitrogen was applied at planting, these diagnostic tools may be less reliable.
In such situations, computer-based nitrogen models, including Adapt-N and the Granular Agronomy Nitrogen Model, can help estimate nitrogen needs using weather data, soil conditions, and management history.
White encourages farmers to compare model recommendations with their standard practices through simple on-farm trials. Evaluating different nitrogen management strategies can help improve decision-making and build confidence in future fertility programs.
Photo Credit: gettyimages-nes
Categories: Pennsylvania, Crops, Corn, Weather