Nitrogen monitoring for higher yields and greater nitrogen use efficiency

Principal Investigator: Ben Rosser

Scientific Summary:

Nitrogen (N) remains a key input in corn and cereal production but determining the rate required remains an elusive target. Weather is a dominant force impacting nitrogen use efficiency in Ontario agriculture.  When weather and nitrate supply from the soil are not factored in to N recommendations the risk goes up considerably that N may be over applied and move in to the environment or it will be under applied and put producer’s economic sustainability at risk. It has become clear as a result of previous research that general recommendations that have no weather or soil N status adjustment are limited in predicting correct N rates beyond “the average.” As farmers move to more in-crop nitrogen fertilization strategies (i.e. side-dressing, high clearance injection tool bars, Y-Drops, etc.) the influence of weather on soil nitrogen status and potential crop demand for nitrogen will become more significant factors in attempting to predict the correct N rate. It is imperative that Ontario has a network of sites that can evaluate how weather data, crop and soil factors and recommendation tools can fit together to improve yields and environmental sustainability. It is increasingly apparent that as weather fluctuations become more severe from season to season, recommendation tools will almost certainly need some real time weather or soil N status data to make accurate recommendations.

The project focused on addressing climate change challenges (precipitation and temperature) and how they impacted decisions on nitrogen application rate for high yielding corn, and nitrogen availability throughout the season. The project also addressed the challenge of improving nutrient stewardship in Ontario, applying the right rate of nitrogen at the right time, through development of new tools and recommendations. The project will improve the farmers’ responsiveness to weather events, to reduce environmental risks that can impact the sector or society at large. Yield expectation combined with soil nitrate status work together to produce a much more reliable N recommendation for the side-dress application.

Lessons learned from this project were incorporated into the annual OMAFRA spring soil nitrate monitoring. All locations were sampled at all five sample times: “planting time” at beginning of May, V1-V2, V3-V4, V6 and V9 stages. While only the early June, pre-sidedress stage of corn is calibrated to Ontario’s pre-sidedress soil nitrate (PSNT) recommendations, soil nitrate monitoring over a longer time may be more beneficial for understanding the trajectory of soil nitrate release than a one-time soil nitrate sampling that could be influenced by weather or other factors. Continuing to track soil nitrates at fixed locations with zero-N plots and continuing to measure nitrogen yield response at the end of the year may continue to provide more valuable insight in N response across years versus a PSNT survey alone.

Lessons Learned:

i) While PSNTs are only calibrated for pre-sidedress stage, repeated sampling over a longer period may help give a better indication of soil nitrate trends/trajectory versus one sampling date at PSNT timing for the annual OMAFRA PSNT survey.

ii) Nitrates are sensitive to handling and should be sent for analysis quickly. Temperature is especially critical, so soil samples must be kept cool to be accurate.

For more information on how to conduct PSNT tests on your farm, contact Ben Rosser, Corn Specialist with OMAFRA.

Project Related Publications

Annual results for the PSNT survey can be found on