Tasmia Kabir, Aaron De Laporte, Joshua Nasielski, and Alfons Weersink. 2021. Adjusting nitrogen rates with split applications: Modelled effects on N losses and profits across weather scenarios. European Journal of Agronomy. doi: 10.1016/j.eja.2021.126328
Study Summary by Tasmia Kabir and Cameron Ogilvie
key messages
- Splitting nitrogen applications and adjusting the second application rate based on weather increased farm profit and reduced nitrogen losses to the environment only in dry years
- Split nitrogen applications increased farm profit between 15 to 20% in dry seasons and one to 16% in wet seasons, compared to pre-plant broadcast
Nitrogen fertilizer use in agriculture has been increasing; unfortunately, the same is true for nitrogen losses to the environment. Weather, as well as the frequency and timing of nitrogen applications, can affect how efficiently nitrogen is used by the crop to produce yield and how much is lost. One way to improve nitrogen fertilizer use in corn is to split the application so that some is applied at planting and the rest is applied in the growing crop. Farmers can then adjust the rate and timing of the second application depending on the weather. The goal is to ensure that there’s never too much or too little nitrogen for the crop to use at a given time. In this study, researchers evaluated how split nitrogen applications might impact farm profitability and environmental losses using computer modeling.
WHAT THEY FOUND
Researchers found that, in corn, using a split nitrogen application and adjusting the second application based on weather could increase farm profits by 15 to 20% in dry seasons and one to 16% in wet seasons compared to broadcasting nitrogen before planting. Comparing application timing, it was more profitable to make the second nitrogen application at the 13th leaf stage (V13) than at 6th leaf stage, except in wet and cold seasons.
Split applications reduced both nitrate leaching and nitrous oxide emissions up to 24%, and ammonia volatilization losses up to 55% compared to pre-plant broadcast. Overall, making the second application at V13 minimized nitrogen losses in all weather conditions. But management that minimized losses to the environment did not always maximize farm profitability. Split nitrogen applications maximized both economic and environmental benefits only in dry seasons.
WHY IT MATTERS
Nitrogen management that maximizes farm profits does not always minimize losses to the environment. In this study, split applications always reduced nitrogen losses to the environment compared to pre-plant broadcast, but this management decision maximized economic and environmental benefits only in dry years. Therefore, while governments should encourage farmers to adopt practices where both farm businesses and the environment are improved, additional policy incentives are needed for when reducing nitrogen losses leads to higher costs to farmers.
HOW THEY DID IT
This study focused on corn yield with three different management practices: 1) traditional pre-plant broadcast (urea); 2) split application at V6 (UAN); and 3) split application at V13 (UAN). The base nitrogen rate was 169 kg nitrogen ha-1 and the second in-season application was adjusted ±20 or ±40 kg nitrogen ha-1 in split application. The study used 19 years of (1999-2018) weather data collected at the Elora Research Station to develop nine weather scenarios. The study analyzed corn yield and nitrogen loss, using the DeNitrification and DeComposition (DNDC) biophysical simulation model. The simulated crop budgets were used to measure the profit of each nitrogen management strategy in this research.
