- Assessing wheat stands in the spring helps optimize nitrogen applications
- Fields with thin stands may benefit from split applying nitrogen
- A single application of nitrogen at Feeke's growth stage 5 can maximize wheat yields when stands are adequate.
Wheat is unique in that it can produce tillers, stems that have the potential to develop grain- bearing heads. Taking stand and tiller counts is important, as it can help determine the optimal timing(s) for nitrogen in the spring. With temperatures trending warmer, growers should consider taking some time to assess wheat stands.
The primary objective of spring nitrogen fertilization for wheat is to ensure sufficient nitrogen is available in the rooting zone before jointing, when the uptake of nitrogen increases significantly. However, nitrogen applications can also stimulate tillering, helping to fill out thin stands and enhance overall yield potential. When producing wheat, the goal is to achieve a stand with optimal tiller numbers and, therefore, optimal yield. The ideal density for a thriving stand of winter wheat ranges from 30 to 35 plants per square foot in the fall. In the spring, tiller numbers of at least 70 per square foot would be considered optimal. When stands have fewer than 70 tillers per square foot, early spring applications of nitrogen can help stimulate tiller production. In these cases, an application of 50 lbs of N per acre in the spring would be suggested, with the remaining balance applied around Feeke's 5. If tiller numbers are optimal, a single application at Feeke's 5 will help ensure optimal nitrogen uptake and yield.
Nitrogen rate recommendations vary by state. For instance, in Illinois, recommendations range up to 90 total lbs of N per acre on high organic matter (OM) soils and up to 150 total lbs of N per acre on low OM soils, with optimal rates depending on wheat grain and nitrogen prices. Higher total nitrogen rates increase the risk of lodging, especially with lush fall growth, and should be split-applied to ensure early nitrogen application. Palisade® Maxx is a plant growth regulator that can be applied at Feekes 4-7 to reduce plant height and improve late season standability. This is recommended when using high nitrogen rates and when the field has a history of manure. Research suggests that application rates may be reduced by 10% on high OM soils with either a single late spring application or split application.
Nitrogen stabilizers should be considered, especially urease inhibitors if urea is utilized and dry conditions are forecasted after application. Yield response to split timing and stabilizers is greater in soil types prone to nitrogen loss and under wet, warm conditions. Slow-release nitrogen forms protect against nitrogen loss and typically result in higher yields, especially with earlier applications. Foliar injury is a concern with UAN applications, particularly when tank-mixing with herbicides. Limit nitrogen when tank mixing with herbicides to 20-30 lbs to minimize issues.
Lastly, sulfur is essential in wheat production, and many fields benefit from sulfur fertilization. Blending dry ammonium sulfate (AMS) with urea or liquid ammonium thiosulfate (ATS) with UAN can provide additional sulfur where deficiencies are observed
Image 1. Wheat Growth Stages and N Uptake Curve (Source: Steve Ebelhar, University of Illinois).
References:
Conley, S. et al. Wheat Tiller Number and Nitrogen Fertilization. https://www.agry.purdue.edu/ext/corn/news/articles.05/WheatTopDressN-0128.pdf
Managing Wheat By Growth Stage. https://www.extension.purdue.edu/extmedia/id/id-422.pdf
Murdock, L. Nitrogen Fertilization of Wheat. https://www.uky.edu/Ag/Wheat/nitrogen.html
Nagelkirk, M. Applying Nitrogen Fertilizaer to Wheat in Early Spring. https://www.canr.msu.edu/news/applying_nitrogen_fertilizer_to_wheat_in_early_spring