Each year that this sensor has been used, the accuracy of the nutrient content of manure has improved, continuing to showcase this technology's potential to improve nutrient use from manure. (Photo: Iowa Soybean Association)
Measuring nutrients during manure application
November 3, 2025 | Lucas De Bruin, CCA
Key Insights
- Understanding the nutrients in manure increases nutrient use efficiency.
- More effectively accounting for manure nutrients reduces input costs and potential nitrate losses to the environment.
One of the most difficult parts of managing manure is accurately accounting for nutrients being applied across the field. Even when agitating manure, one cannot achieve a perfectly consistent nutrient profile. Over the past three years, the Iowa Soybean Association's (ISA) Research Center for Farming Innovation (RCFI) and Iowa State University (ISU) have worked with farmers and custom applicators to evaluate the consistency and accuracy of the manure constituent sensing technology.
The technology uses the Harvest Lab 3000 sensor, which uses Near Infrared Reflectance (NIR) to measure nutrient content of the manure.
As the manure flows through the applicator, the infrared light interacts with the nutrients and is reflected to the sensor. Based on that analysis, the nutrient levels are determined, and the applicator can adjust gallons applied per acre as needed.
The sensor measures total nitrogen, ammonium nitrogen, phosphorus, potassium, dry matter and volume. There are also three options for Manure Sense to control the application. Users can set it for "limit P" and it will not exceed the threshold operators set for phosphorus. Set to "target N" and it will adjust the volume of manure to apply the desired nitrogen rate. The volume selection applies a static rate of manure while recording as-applied information based on the nutrient content read by the sensor.
As with many pieces of precision sensing equipment, there is a calibration curve. As more data is collected, the calibration curve can be updated, resulting in more accurate sensing.
Over the course of this trial RCFI has partnered with ISU to improve the calibration of this technology by collecting manure samples and correlated the sensor readings with lab readings of the manure samples. We have seen an improvement in sensor accuracy since we began this work in 2023. The table accompanying this article shows Manure Sense values versus the lab results year over year. You'll note that the percent difference in values between the sensor accuracy and lab results has decreased each year since the project began in 2023, indicating greater accuracy in the sensor technology.
While the sensor readings are not perfectly aligned with lab analysis of the manure, it does allow us to better understand the variability of the manure source being used and where the most nutrient-rich or diluted manure is placed within the field. This capability allows livestock operators to be better stewards of their manure and more prescriptive with synthetic fertilizer applications.
ISA has run multiple on-farm trials comparing corn fields using manure and manure with an additional 50 pounds of synthetic nitrogen applied from 2006-2014. These trials showed a consistent yield benefit when adding 50 pounds of nitrogen in addition to manure.
Using this Manure Sense technology, farmers can see how the composition and placement of their manure affect nutrient levels. The program helps applicators generate a variable rate synthetic nitrogen prescription based on where nitrogen could supplement diluted manure in specific areas of the field instead of a flat rate across the entire field.
Considering current market prices and input costs, accounting for the nutrients your field is receiving from manure can help farmers more effectively utilize this resource, saving costs associated with nitrogen and other inputs.
Interested in how you can utilize your manure resource more efficiently and effectively? Reach out to RCFI to learn more about this technology.
Written by Lucas De Bruin.
Back