Nitrogen: A limiting factor for crops that has implications for the environment
Nitrogen is essential for crop growth, but in excess, it can harm the environment. Nitrogen is also the most limiting nutrient for crop production in Canada and so is usually applied in the largest quantities compared to other elements. Therefore, understanding how to manage it is important to both farmers and those concerned about the environment.
Researcher Dr. Mervin St. Luce of the Swift Current Research and Development Centre is advancing our knowledge of soil nitrogen cycling and plant nutrient uptake mechanisms in order to develop site- and cropspecific nitrogen management guidelines. With these science-based tools, farmers can make better-informed decisions on how best to manage their nitrogen fertilizer utilization.
“My research aims to improve nitrogen use efficiency by matching crop nitrogen demand with nitrogen supply from soil, from fertilizer added, from crop residue decomposition, and biological fixation by legumes.” said Dr. Mervin St. Luce, Research Scientist, Agriculture and Agri-Food Canada.
Different crops interact differently with nitrogen
Different plant species require different amounts of nitrogen to obtain the greatest potential yield. Dr. St. Luce, along with colleagues from across Canada, has obtained research funding through the Diverse Field Crops and the Canola Agri-Science Clusters of the Canadian Agricultural Partnership for work on advancing our knowledge of nitrogen use efficiency in plants.
The nitrogen requirement versus yield relationship is determined through research trials and provided to producers as a nitrogen response curve. As new highyielding varieties of well-studied crops are released, such as wheat and canola, new response curves need to be determined. However, for less common (diverse) crops, including camelina and sunflower, much less is known about the relationship between nitrogen requirements and peak yield potential, so more research is needed to determine the most efficient use of nitrogen fertilizer.
Teaming up with Dr. Bao-Luo Ma of the Ottawa Research and Development Centre, Dr. St. Luce is coleading a project that will provide canola producers with a complete information guide of site-specific nitrogen management practices for different agri-ecozones. This project will investigate the critical roles of root architecture in nitrogen absorption, root anchorage strength (involved in lodging resistance) and trait variations. At the same time, Dr. St. Luce and Dr. Ma will be testing soil and plant diagnostic tools used in assessing nitrogen sufficiency. Studies are also looking at how pulse crops, such as field peas, chickpeas, lentils and beans that are able to “fix” (add back) nitrogen in the soil, play into the nitrogen cycle.
Different farming practices also impact nitrogen use efficiency
Perhaps even more important than the type of crop grown is the influence of agricultural management and other human activities.
“From the way nitrogen fertilizer is applied, to the form and rate at which it is applied, to the treatment of crop residue (such as straw and chaff left after the crop is harvested), to the choice of herbicides or whether to use organic cropping methods, the farming practices chosen have a big impact on nitrogen,” said Dr. St. Luce.
One way to study how nitrogen moves through the crop and soil is by using Nitrogen-15 isotopes as a tracer. In partnership with other AAFC scientists, Dr. St. Luce is using this technique to simultaneously trace and accurately quantify nitrogen derived from above-ground and below-ground crop residues left in the field, as well as from nitrogen fertilizer applied to crops. This will help to quantify the amount of nitrogen a farmer should expect in the soil after growing a pulse and how long it will be there, as well as a comparison of leaving – or not leaving - pulse crop residues on the ground. Additionally, results from this study will provide a better understanding of the fate of nitrogen fertilizer applied to crops with respect to the cropping system and application rate.
• Nitrogen is the most limiting nutrient for crop production and is usually applied in the largest quantities.
• Nitrogen management is very important because nitrogen that is not taken up by crops is susceptible to be lost from the soil plant system through various pathways, and can affect air and water quality.
• AAFC research aims to improve nitrogen use efficiency by matching crop nitrogen demand with nitrogen supply from soil, from fertilizer added, from crop residue decomposition, and biological fixation by legumes.