Agronomy Update Features
Agronomy update: Nitrogen management strategies for spring wheat

New, high yielding spring wheat varieties require nitrogen (N) fertility programs that can deliver upwards of 200 lbs N/ac  (224 kg/ha) to ensure yield is maximized and high protein levels are achieved on the eastern Prairies.

To investigate N management strategies for high yielding spring wheat, Amy Delaquis (Mangin) conducted field trials at the University of Manitoba Ian N. Morrison Research Farm in Carman, Man., and in a commercial field near Manitou, Man., in 2018 and 2019 as part of her PhD program with Yvonne Lawley and Don Flaten at the University of Manitoba.

The first objective of this study was to determine N uptake, accumulation and remobilization patterns in spring wheat, and how these patterns are influenced by agronomic practices, such as N management and PGR application. The second was to measure the N use efficiencies for grain N production and potential for improvement through agronomic management.

AAC Brandon (CWRS), AAC Cameron (CWRS) and Prosper (CNHR) were compared. AAC Brandon has high yield potential, high protein and very good lodging resistance. AAC Cameron is a tall variety with good lodging resistance and high yield and protein. Prosper has high yield but lower protein content, and lodging resistance rated as good.

Soil was sampled at 0 to 6, 6 to 24, and 24 to 48 inches (0-to-15-, 15-to-60-, and 60-to-120-cm) depths for residual soil nutrient analysis in the spring before planting.

Seed-placed phosphorus (P) was applied as mono-ammonium phosphate (11–52–0) at a rate of 40 lbs P2O5/ac (45 kg P2O5/ha) for all plots. Herbicides and fungicides were applied as necessary.

In addition to the check plot with 0 N fertilizer application, a standard rate of 140 lbs N/ac (156 kg N/ha) and a reduced rate of 70 lbs N/ac (78 kg N/ha) were applied as conventional urea, midrow banded at planting. A blend of ESN, a polymer-coated urea and conventional urea at rates of 100 lbs N/ac as ESN plus 40 lbs N/ac as urea (112 kg N/ha:44 kg N/ha) was applied through midrow banders at planting to evaluate N source. To evaluate application timing, a split application of 70 lbs N/ac was applied as conventional urea through midrow banders at planting with the remaining 70 lbs N/ac applied broadcast on the soil surface as SuperU at flag leaf.

All combinations of varieties and N treatments were compared with and without a PGR, Manipulator 620 (chlormequat chloride), applied at the onset of stem elongation (GS 31).

Nitrogen management strategies of rate, source and timing did not differ statistically, and yields were roughly around 75 bu/ac (5000 kg/ha). The 0 N check was statistically lower at 60 bu/ac (4032 kg/ha). Yields during the two years were lower than normal due to dry conditions with precipitation at 68 to 78 per cent of the long-term average. This can explain why the reduced N rate was statistically similar to the standard N rate applications, especially since spring nitrate-N values ranged from 63 to 80 lbs/ac (71 to 90 kg/ha) in the 0 to 48 inch soil profile.

There were differences in grain protein content as influenced by N treatments. The highest average grain protein content was with the split application at 14.1 per cent. The standard and ESN blend treatments were statistically similar at 13.6 per cent. The reduced rate was 12.4 per cent and the check at 11.1 per cent.

The application of a PGR significantly increased grain yield from 71 to 72 bu/ac (4746 kg/ha to 4837 kg/ha), although, agronomically, this small increase would be insignificant. This increase in yield, however, resulted in a significant decrease in grain protein content from 13.1 per cent in the untreated to 12.9 per cent with a PGR application.

At standard high rates of N, the average N uptake efficiency was 80 per cent and the N use efficiency was also 80 per cent. Under the conditions of this trial, this shows that only 60 per cent of the N available to the crop (excluding mineralized N) is being used for grain N production during the growing season. Most of the remaining N was probably left in the crop residues and soils.

Nitrogen uptake post anthesis was 21 to 36 per cent of the total growing season N taken up, but this post anthesis uptake was highly dependent on environmental conditions.

Overall, N management and PGR applications had little impact on N remobilization during grain fill. As a result, pre-seed or side-band application of N fertilizer at seeding remain the most efficient methods to manage N fertility in the Black soil zone of the eastern Prairies, and producers should focus on management practices that promote early season N uptake. 

Bruce Barker divides his time between CanadianAgronomist.ca and as Western Field Editor for Top Crop Manager. CanadianAgronomist.ca translates research into agronomic knowledge that agronomists and farmers can use to grow better crops. Read the full Research Insight at CanadianAgronomist.ca.