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Evaluating plant and soil sensors for determining site-specific nitrogen strategies

Principal Investigator: Greg Stewart

Research Institution: Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)

Timeline: October 2013 – December 2015


  • Demonstrate new technology in the field and encourage industry and farmers to adopt new beneficial management practices. Innovative leading edge technologies will be demonstrated in this project (1) plant sensors for real-time Nitrogen application (e.g., GreenSeeker TM), and (2) soil sensing/mapping (Soil Optix).
  • Determine the benefit of site-specific application of nitrogen on corn: evaluating variable rate application, management zones within fields and late-season split applications.


  • The validation of whether these new technologies are effective at predicting N response and N rate may help improve a farmer’s financial performance relative to straight-rate applications by reducing inputs where expected response is low and increasing inputs where expected response is high and reduce their environmental impact. 

Scientific Summary:

Applying the proper rate of nitrogen (N) at the proper time in efforts to maximize yields while minimizing excess N has long been a pursuit in corn production. Corn growers already know the timing and application rates of N are key to maximizing yield. Most in N Ontario is applied before corn planting, or pre-plant. And N is applied to approximately 20 per cent of Ontario corn acres at side-dress time, when N is injected between rows at the six-leaf stage. And since corn does not start using N in significant quantities until it is knee high, or after June 20 in Ontario, there is interest in finding new ways to apply N in later growth stages to reduce the chances of losing it before the crop really needs it. Early application of N can result in delayed uptake relative to application timing which allows for losses of N availability due to leaching and denitrification. Advanced technology has opened up a new nutrient application window in corn, beyond waist height. And interest in applying N just before plant demand is at its highest is growing. This later application places N into the system at a more optimal time relative to crop need.

This project evaluated new site-specific sensor technologies (i.e. in-field plant and soil sensors) that can help farmers utilize their crop inputs more effectively and efficiently while reducing environmental load. The goal was to adapt new sensor technologies from the US and Europe through developing algorithms and/or calibration protocols that better suit Ontario climatic and soil conditions. It was anticipated that use of these innovative technologies will offer the opportunity to make applications of N to corn later in the growth stage of the crop than has been traditionally possible. This project focused on field scale variable rate nitrogen application for corn in three site locations across Ontario in Langton, Forest and Brucefield have been set up to test the three N application windows – pre-plant, side-dress and above waist height. Firstly, this project demonstrates the value of doing PSNT sampling and then making side dress prescriptions. In some instances, PSNT values appeared to have a strong relationship with zero N yields, suggesting they may be an effective tool for trying to gauge soil N supply. Secondly, environmental benefits relate to feeding the corn crop at a stage when the requirement for N is highest (V8-V10) stage. This project demonstrated several different timing opportunities to test on the farm, either as a standard blanket application or as a variable rate application using 2 different sensing technologies. Thirdly, data analysis was a large task and drawing overarching conclusions from site-specific studies is difficult and very laboursome. Many of the collaborating industry partners had a hard time validating the technologies because good yield data is not being collected on a large number of farms in Ontario and if it is being collected no one is mining that data for real information. The “big farm data” paradox was observed in this project. Finally, later season N application is not paying back uniformly across every farm field in this project. In fact, site-specifically across each site there are areas of the field that returned substantial value of the technology to the farmer, and then areas of the field where this technology isn’t necessary, i.e. high organic matter, sufficient seasonal moisture, lots of mineralizable N areas in the field. This makes sense as the technology is designed to apply the N that is required by the plant; it is an optimization process.

External Funding Partners:

The Ontario Farm Innovation Program is funded through Growing Forward 2 (GF2), a federal-provincial-territorial initiative. The Agricultural Adaptation Council assists in the delivery of GF2 in Ontario.

Project Related Scientific and Popular Publications:

Jeanine Moyer. “N application in corn: Researching Precision Agriculture Strategies.” Ontario Grain Farmer magazine, August 2014.

Treena Hein. “Improving late nitrogen application: Crop vigour sensing technology is a promising way to diagnose N requirements.” Top Crop Manager magazine, April 2015.