In the Field
Controlled-Release Nitrogen: The New Norm?
Researchers are studying application processes to provide nitrogen—one of the most important nutrients in potato production— in new, more efficient and less labour-intensive forms.
A CONSISTENT SUPPLY of nitrogen in potato production throughout the growing season is one of the most important factors for optimum tuber yield and size. Potato fields require a modest amount of nitrogen during the early part of the growing season for adequate canopy development, while nitrogen applied in excessive amounts at this time is at risk of being lost before the crop can take it up.
Once the tubers are formed and begin bulking, potato plants require a steady supply of nitrogen for proper development. Deficiencies in nitrogen at this time can reduce canopy growth, resulting in reduced yields. Widely fluctuating levels of nitrogen can also cause irregular growth as well as tuber deformities. The level of nitrogen in the plant late in the growing season is also important because high nitrogen levels at this time can delay crop maturity and prevent tubers from forming an adequate outer layer of skin on the tubers. Therefore, proper application of nitrogen is key to a grower’s bottom line.
Most nitrogen fertilizer is applied at or before planting, with the remainder applied during the growing season based on need. Controlled-release nitrogen sources are a class of nitrogen fertilizer that may eliminate or reduce labour-intensive and costly in-season applications, as well as increase nitrogen-use efficiency. This type of fertilizer releases nitrogen at controlled rates to match the timing of nitrogen uptake in order to maintain maximum growth in plants, while minimizing nitrogen loss.
New Nitrogen Alternative
Fertilizer in the form of polymer-coated urea allows water to enter and dissolve the urea in a controlled release throughout the growing season. The polymer coating helps to prevent nitrogen loss, including leaching. The purpose of this type of controlled-release technology is to ensure nitrogen is available to the potato plant as it grows, and to have an adequate supply of nitrogen as the plant requires it throughout the growing season. However, studies in North America are showing mixed results, depending on the length of the growing season and soil profiles.
Bernie Zebarth, research scientist at Agriculture and Agri-Food Canada’s Potato Research Centre in New Brunswick, and his colleagues are looking at the use of polymer-coated urea in potato production. “Depending on soil type—for example, in sandy soils—the polymer-coated urea does show a yield benefit to the crop,” he says. “Our studies have seen good results on soils with a high risk of leaching losses, and, overall, can save yield and tuber quality in those conditions.”
However, Zebarth notes that in other soil types the results have not been as pronounced, producing yields similar to that of regular nitrogen applications.
Polymer-coated urea applications are more expensive than regular nitrogen, and, as a result, growers have not been quick to accept this new form of fertilizer. “In soils with a lower risk of nitrogen loss, it is not clear if the benefit of the controlled-release fertilizer justifies the additional cost,” explains Zebarth. “It’s a tough sell to producers if it doesn’t improve or benefit their bottom lines,” he says.
Future Environmental Benefits
Zebarth’s studies are also focusing on environmental aspects of polymer-coated urea, such as reduced nitrogen leaching and reduced greenhouse gas emissions of nitrous oxide. Zebarth and his colleagues across Canada are comparing the use of banding nitrogen at planting with split nitrogen applications and banding polymer-coated urea at planting.
Fertilizer inputs can cause large emissions of nitrous oxide, which is a potent greenhouse gas. Specialized coated urea fertilizer products are designed to release nitrogen slowly over the growing season, better matching nitrogen supply to plant uptake. The Canadian researchers are currently conducting studies to determine if this slower release of nitrogen will result in lower nitrous oxide emissions.
Zebarth notes that in the future the environmental benefits of using controlled-release fertilizers may offer new advantages for producers, such as credits for reduced greenhouse gas emissions. “If reductions are significant enough, in terms of emissions, by using these types of products … it may pay off in other benefits to the producer other than in yield,” explains Zebarth.
Potatoes are not the only crop being tested in Canada using this type of fertilizer. More studies are planned on other crops in both eastern and western regions of the country to help producers make informed decisions about nitrogen management options for their crops. Controlled-release nitrogen fertilizers are significant in that they may offer a possible mechanism for growers to meet their potato crops’ nitrogen needs with improved efficiency and profitability, and less environmental risk and labour.