Early Nitrogen Deprivation and Wheat Root Systems

Two multi-year research projects were executed with a focus on a) the impact of delayed nitrogen application on winter wheat grain yield and protein and b) the partitioning of nitrogen uptake and distribution in winter wheat varieties with inherently high or low wheat protein values. The first research project demonstrated that across 31 trials, a pre-plant nitrogen application resulted in the highest grain yield only twice. An in-season application near or after the first hollow stem (FHS) stage increased grain yield seven times more than that of the pre-plant application. Furthermore, a delay in nitrogen application until the FHS stage resulted in a significant increase in wheat protein concentration in 21 of the 31 trials. The second project is showing that the higher protein varieties, Doublestop CL Plus and Green Hammer, take up more nitrogen after anthesis than the lower protein varieties, Iba and Gallagher. 

 

Those results drove additional research to help Wheat Improvement Team members better understand the impact of genetics on the response to delayed nitrogen application. Based on the precedent set in Brassica and Gossypium species, plants under nitrogen stress may reduce vegetative or shoot growth in favor of root growth. A preliminary experiment was designed to test a high-throughput method for evaluating the effect of early nitrogen deficiency on wheat growth among four varieties known to have differing nitrogen uptake patterns and nitrogen use efficiency. Seeds were planted into tree cone pots and rock wool was used as a synthetic soil base. The cones were arranged in trays, which were placed into nutrient-solution containers with or without nitrogen in a controlled climate room for 30 days (Figure 1). After 30 days, the roots were separated from the rock wool, and shoot and root lengths were measured (Figure 2) then dried for weighing. 

 

 

 

This method proved to be moderately successful in detecting the impact of early nitrogen deprivation on wheat growth. However, the use of cubed rock wool presented a challenge, because the roots could not be easily detached, and many fine fibrous roots were lost. If a better media could be found, this method could be adapted to evaluate 16 to 20 varieties every 30 to 45 days. Due to challenges in separating root tissue from the rock wool, excessive experimental error was introduced to a point that no significant difference could be detected across varieties or nitrogen treatments (Table 1).