By Timothy Harrigan
The economic pressures of farming have caused Michigan crop growers to consider new ways to increase yield and profitability. While nitrogen management is essential, interactions between the soils, weather, plants and other management decisions determine full yield potential. Interest in crop sensing technologies designed to feed the corn crop the right amount of nitrogen, when the crop needs it, has gained the confidence of many growers. Sensors that estimate crop nitrogen needs drive variable rate application (VRA) applicators on the go based on crop chlorophyll content—this has simplified nitrogen management.
Advantages of sensor technology are that less labor is needed compared to the pre-sidedress nitrogen test (PSNT), and it eliminates the lag time between measurement and application. Closing the lag gap reduces the risk of yield- and profit-robbing nitrogen loss from leaching and nitrogen loss to the atmosphere with excessive rain when nitrogen is applied pre-plant or early in the growing season.
Sensors are typically positioned directly over a cornrow. The sensors measure light reflected by the crop canopy, so the best results come with applications made at or after growth stage V6. The sensors have a light source, so they work equally well in low light as in full sunlight. Information from the sensor adjusts the nitrogen application rate on the go.
Typically, one-third to one-half of the expected nitrogen needed for the season is applied at planting with the remainder delivered at sidedress time based on information from the sensor. Growers need to create a well-fertilized nitrogen reference strip in each field at planting time as a benchmark or calibration strip for that field to “train” the sensor about variability in the field.
Blaine Baker, Lenawee County no-till grower, began testing on-the-go nitrogen sensing on a small portion of his farm about 10 years ago. Retaining nutrients in the root zone and improving nitrogen use efficiency for profitability and protecting the environment are a high priority on the farm. All fields are grid soil sampled regularly, and commercial fertilizers are applied as close to planting as possible using VRA. Split applications of nitrogen on the corn ground include a portion applied through the planter with makeup sidedress nitrogen.
Previously, makeup nitrogen was based on the pre-sidedress nitrogen test (PSNT). As confidence grew in on-the-go nitrogen sensing technology, PSNT acreage dropped and sensor acreage increased. Now, all sidedress nitrogen is sensor-based. Total nitrogen per acre has decreased, but the most significant benefit is in getting the right amount of nitrogen in the right place. Applying a flat rate based on expected yields may be correct on average, but over-apply in low-yielding areas and under-apply in others.
On-the-go nitrogen sensing technologies can be an essential part of an effective nutrient management program. Attendees at the Michigan State University Ag Innovation Day
on July 26, 2019, on the campus of MSU will have an opportunity to interact with the nitrogen sensing technology, learn about the economics of VRA-nitrogen versus single-rate applications from a few Michigan growers, and take home practical recommendations for implementing VRA-nitrogen technologies.