Good afternoon!
We are happy to have our Field Crop Specialist Caitlin Congdon disseminate our data from a recent OFCAF Demonstration in corn. We are hoping this can be some food for thought while thinking about your corn nitrogen requirements and the timing of those applications.
In 2024, a demonstration trial was conducted in Colchester County to look at the impact of nitrogen topdress application rates in corn. Similar to a strip trial that could be conducted on farm, the purpose was to try to assess the rates at which nitrogen was not limiting yield but not being applied in excess either. Having a better understanding of the impact of this application rate should provide both economic and environmental benefits. There are many factors that may contribute to efficient nitrogen uptake and use in any given year, such as the weather conditions at and directly after application, how much nitrogen was applied as a starter or available from other sources like manure, the source of nitrogen used in the topdress, etc. This demonstration offers a snapshot of what was happening in the demo field and provides a starting point for figuring out the best nitrogen topdress rate on your farm.
The demonstration field had 24 units of nitrogen at planting and a credit of 60 units of nitrogen from dairy manure applied prior to planting. Topdress application rates ranged from 0 kg/ha to 210 kg/ha of urea, which translates to 0-96.6 kg/ha of actual nitrogen (Table 1) adding up to a total nitrogen application for the season of 0-180.6 kg.ha. Topdress fertilizer was broadcast applied on July 4th when the corn was at the 3-4 leaf stage (Figure 1).
Table 1. Nitrogen application rates on corn demo field, 2024.
|
Topdress Application Rate of Urea (kg/ha) |
Topdress Application Rate of Actual Nitrogen (kg/ha) |
Total Seasonal Nitrogen Applied (kg/ha) |
| 0 | 0 | 0 |
| 30 | 13.8 | 97.8 |
| 60 | 27.6 | 111.6 |
| 90 | 41.4 | 125.4 |
| 120 | 55.2 | 139.2 |
| 150 | 69.0 | 153.0 |
| 180 | 82.8 | 166.8 |
| 210 | 96.6 |
180.6 |
Figure 1. Topdress fertilizer applied using an ATV-mounted broadcast spreader, July 4, 2024.
Leaf tissue samples were taken prior to topdressing to determine the amount of nitrogen in the plants. Nitrogen content ranged from 4.03-4.50% in the tissue samples, indicating that there was fairly even nitrogen uptake by the plants in the early part of the season.
Stalks in one meter of row were cut at about 6” from the ground and weighed to simulate corn silage harvest in three areas in each plot. Assuming an average moisture content of around 65%, yields on a dry weight basis ranged, on average, from 16.6-29.3 mt/ha (6.7-11.9 mt/ac) in the 0 kg/ha and 210 kg/ha treatments respectively (Figure 2). This result makes sense because higher nitrogen rates generally correspond to higher yields and corn requires a minimum of 115 units of nitrogen (NS Provincial analytical lab recommendation) which should be adjusted upward based on the yield potential of the crop. Looking a little closer, there’s more to the story. The error bars on the graph show the variability between data points, which in this case are the yields from the three subplots in each treatment. Since this demonstration wasn’t replicated, field variabilities such as wet spots, uneven fertilizer application, or wildlife damage can easily skew the results. It is likely that with more data points for each topdress application, the 90, 120, and 150 kg/ha urea topdress treatments could have had average yields that were closer to those in the 180 and 210 kg/ha treatments. If similar yields were achieved with varying urea topdress rates, the lowest rate would be the best choice environmentally and economically. Therefore based on the results of this demonstration there was potential to reduce the nitrogen topdress rate without incurring a significant yield penalty.
Figure 2. Dry matter plant yield of corn silage by urea topdress application rate, 2024.
Fertilizer price per hectare and per acre were calculated using a spring 2024 price for urea of around $860/mt (Table 2). The difference in average yield was just 2 mt/ha more in the 180kg/ha treatment (27mt/ha) compared to the 60kg/ha treatment (25 mt/ha), but the difference in fertilizer price for those two topdress applications is almost $100. In this scenario, it would be much more economically sustainable to opt for the 60kg/ha treatment. From an environmentally sustainable perspective, achieving a similar result with 120 kg less fertilizer suggests better nutrient use efficiency and less loss to volatilization and leaching.
Table 2. Price of urea fertilizer by application rate, spring 2024.
| Urea Application Rate (kg/ha) | Fertilizer Price/ha ($) | Fertilizer Price/ac ($) |
| 0 | 0 | 0 |
| 30 | 25.80 | 10.45 |
| 60 | 51.60 | 20.89 |
| 90 | 77.40 | 31.34 |
| 120 | 103.20 | 41.78 |
| 150 | 129.00 | 52.23 |
| 180 | 154.80 | 62.67 |
| 210 | 180.60 | 73.12 |
The results of this demonstration are not meant to suggest a specific nitrogen topdress rate that should be applied across all fields and farms, but rather to show that more fertilizer does not necessarily result in an equal increase in yield, so the economic and environmental factors should be considered in the decision of how much nitrogen to topdress on corn. Other variables that could be considered in a similar field setup include more precise placement of the fertilizer, or the use of enhanced efficiency fertilizer products.
A big thank you to our amazing field research team including the OFCAF research technician Lindsay Scott who is so on the ball with sampling and data collection.
This demonstration was made possible by Agriculture and Agri-Food Canada through the Agricultural Climate Solutions – On-Farm Climate Action Fund (OFCAF). The goals of the program are to encourage on-farm sequestration of carbon and reduction in greenhouse gases through the implementation of improved nitrogen management, enhanced cover crop adoption, and the normalization of rotational grazing. For more info on the OFCAF program, please visit ofcaf.perennia.ca