Efficacy of Fall versus Spring Nitrogen applications
Cristie Preston, Ph.D.
Agriculture has always been an integral part of Dr. Cristie Preston’s life. She grew up in southwest Virginia and had interest in crop and animal agriculture since an early age. Once she began college, she initially chose to study animal science but switched to soil science. Dr. Preston attributes her decision partly to an influential professor who told her, “You can’t understand animals until you understand what they eat.” She received a Bachelor of Science degree in animal science and a Master of Science degree in crop and soil environmental science from Virginia Tech. Dr. Preston holds a Ph.D. in agronomy, focusing on soil fertility from Kansas State University. While completing her advanced degrees, Dr. Preston conducted more than six years of field and lab research. Dr. Preston has experience in laboratory research measuring volatility loss from urea-based fertilizers. Her field research has focused on phosphorus availability and the interactions with tillage and placement. She also has extensive experience in working with large data sets and analysis. Her main priority is helping growers to identify yield-limiting factors and fix those issues as cost efficiently as possible.
The age-old question of which is better: fall or spring applied nitrogen. The short answer is, it depends. Everything from nitrogen source, soil type, and weather conditions can affect nitrogen availability and loss.
The University of Nebraska-Lincoln (UNL) offers these factors to consider if planning on fall and winter nitrogen applications.
- Apply anhydrous ammonia because it’s not initially leachable.
- Apply after soil temperatures are below 50°F. (Check CropWatch Soil Temperatures for your area.)
- Because of the potential for N loss, UNL N recommendations for corn are increased by 5% when applied in the fall.
- Fall applications of nitrate (NO3) forms of N are discouraged due to substantial risk of leaching and denitrification.
- Fall N applications are not advisable on sandy or other easily leachable soils, or where surface ponding occurs.
- Nitrification inhibitors can help reduce the potential for loss through leaching or denitrification, but fall applications are less effective than spring applications.