Maximizing spring wheat productivity
Management strategies such as split N application and the use of a plant growth regulator can help reduce lodging while maximizing yield and protein in spring wheat production.
Farmers are achieving higher wheat yields today than in the past; however, there remains a gap between yields achieved and yield potential of current high-yielding cultivars. As yields rise, nitrogen (N) fertilization has increased to maintain protein content, but higher amounts of N lead to increased risk of lodging and N fertilizer losses.
Using a plant growth regulator (PGR) has gained popularity as an option to manage lodging risk in-season as weather conditions change. A research study was established in order to understand how high-yield wheat management practices, specifically N fertilization strategies and the use of a PGR, affect grain yield and lodging. In addition, yield components were evaluated to determine their individual responses to overall grain yield.
In 2018 and 2019, experiments were set up at Carman and Manitou, Manitoba. The spring wheat cultivars grown were AAC Brandon (CWRS, semi-dwarf, good lodging resistance), AAC Cameron (CWRS, similar to AAC Brandon for yield and protein, taller cultivar with higher lodging potential than AAC Brandon), and Prosper (CNHR, semi-dwarf, lodging rating similar to AAC Cameron).
Five N fertilizer treatments applied:
- Check – 0 N fertilizer
- Standard practice – 140 lbs. N/ac as urea midrow banded at planting; represents a typical N fertilizer rate, timing and sources used for targeting high yields in MB
- Reduced rate – 70 lbs. N/ac as urea midrow banded at planting
- ESN blend – 100 lbs. N/ac as ESN blended with 40 lbs. N/ac urea midrow banded at planting
- Split N application – 70 lbs. N/ac at planting midrow banded as urea and 70 lbs. N/ac at flag leaf surface broadcast as SuperU (urea with urease and nitrification inhibitors)
All cultivar and N treatment combinations either received or did not receive a PGR application. The PGR treatments were sprayed at the start of stem elongation (Zadoks growth stage 31, first node detectable and 1 cm above tillering node) using chlormequat chloride (Manipulator).
All plots were intensively managed to maximize yield.
Grain yield and protein
Growing season precipitation in both years of the experiment was below normal, with site-years receiving between 51 and 78% of the 30-year long-term average rainfall. Site-year (environmental conditions) had a significant effect on grain yield and also accounted for the highest amount of variability in yield. Between cultivars, AAC Brandon and Prosper were significantly higher yielding at around 73 bu/ac compared to AAC Cameron at 67 bu/ac.
While there were no significant yield differences found between the N management treatments, other than the check, the reduced N treatment trended towards lower yields. The researchers noted that in wet years when N losses are more likely to occur, the ESN and split N treatments could potentially produce higher yields than the standard N treatment.
Grain protein was significantly affected by N management, with the split N application increasing protein by 0.5% (14.1%) over the standard rate and the ESN blend (both 13.6%), followed by the reduced N rate, (12.4%) and finally the check (11.1%).
Applying a PGR significantly increased grain yield, although PGR application accounted for only 0.3% of the variation in grain yield in this experiment and was marginally higher at 1.4 bu/ac yield increase with the PGR application. Greater yield differences from using a PGR would be expected in years of higher lodging pressure due to reduced lodging-induced yield loss.
Yield components and relationship to yield
The researchers looked at the yield components of plant density, spikes, kernels, and kernel weight to see how they impacted yield.
The only significant factor that impacted plant density was cultivar, even though seeding rates were based on each cultivar’s seed lot germination, kernel weight, a 15% mortality factor, and a target plant density of 25 plants/ft2 (250 plants/m2). Plant density ratings were: AAC Brandon (23.4 plants/ft2) > AAC Cameron (21.5 plants/ft2) > Prosper (18 plants/ft). Dry spring conditions during this study led to slow and uneven emergence, and Prosper may have been less able to mitigate these effects.
Because of the differences in plant density between the cultivars, there were significant differences in the number of spikes per plant, rated as: Prosper (2.6 spikes/plant) > AAC Brandon (2.0 spikes/plant) > AAC Cameron (1.9 spikes/plant).
All N fertilizer treatments significantly increased the number of spikes per plant compared to the zero N check with no differences between the treatments that had fertilizer N applied. This finding meant that all treatments with N fertilizer applied provided adequate nutrition early enough in the season when the number of spikes were being determined in the plant.
There was a highly significant positive correlation between the response of spikes per plant and grain yield response to changes in N management and PGR application. When considering what management strategies could be done to increase wheat production, this study showed that practices that lead to more spikes per plant will have the highest potential to boost grain yield.
Site-year (Environment) had a significant effect on kernels per spike and accounted for 52% of the response variation. Cultivar also had a significant influence, with AAC Brandon having the most kernels per spike (33.2) compared to both AAC Cameron (31.2) and Prosper (31.0).
The number of kernels per spike was significantly higher in the standard N rate and the ESN treatments compared to the check. Of note, the split N treatment did not differ in kernels per spike from either the reduced rate or the check treatments, suggesting that the second N application at flag leaf timing was too late to provide sufficient N for kernel development.
Applying a PGR also significantly increased the number of kernels per spike. Since this number is being set by the plant during the stem elongation stage, it is likely that resources are being reallocated from stem elongation to kernel development when a PGR is applied, resulting in a crop with increased kernels per spike and shorter stems.
Of all the yield components measured, kernels per spike had the most consistent correlation with grain yield, meaning that as the number of kernels per spike increased, so did the yield.
Site-year had a significant effect on kernel weight, and interactions between site-year, N management, and cultivar were also apparent. Depending on the cultivar and the environmental conditions at each site-year, the kernel weight responded differently to N treatments, with AAC Cameron showing the most response to changes in kernel weights.
Due to the PGR application increasing kernels per spike, the kernel weight from the PGR treatments were significantly reduced, as competition for limited resources between kernels becomes more apparent.
Because of the dry conditions, lodging only occurred and was able to be rated at one site-year after a heavy rainfall event in late July. Canopy height and stalk strength were measured as additional indicators of lodging risk.
Canopy height rankings in this study matched the cultivar descriptions, with AAC Cameron being the tallest, followed by Prosper, then AAC Brandon. AAC Brandon had significantly stronger stalks at anthesis than the other cultivars, but by maturity, no differences in stalk strength were found between cultivars.
Nitrogen fertilizer did not have an effect on canopy height. Nitrogen treatments where the high rate of N was applied had significantly more lodging, regardless of the N source (urea vs ESN blend) or application timing (spring vs spring + flag leaf application), although the split application reduced lodging compared to the ESN blend. The split application showed a general trend toward lower lodging, thought to be attributed to less early-season vegetative growth. However, no differences in stalk strength were found between the standard N rate and the split N treatment or the ESN blend.
Using a PGR significantly decreased lodging in all treatments where a high rate of N was applied. Canopy height was significantly reduced by 2 inches (5 cm) on average, with the tall cultivar AAC Cameron having a 2.5 inch (6.5 cm) reduction and the semi-dwarf cultivars AAC Brandon and Prosper being reduced by 2.2 inch (5.6 cm) and 1.5 inch (3.9 cm), respectively. Stalk strength at anthesis was also significantly greater with a PGR application but no difference in stalk strength was observed at maturity.
Overall, growing season conditions had the largest influence on final grain yield and lodging risk in this study. However, when a high rate of N was applied, split application between planting and flag leaf was found to reduce lodging and increase protein without compromising yield. The use of a PGR when high rates of N are being applied is beneficial to reduce lodging while increasing grain yield due to more kernels per spike.
Funding for this study was provided by Manitoba Crop Alliance.
Mangin, A., Brule-Babel, A., Flaten, D., Wiersma, J., & Lawley, Y. (2022). Maximizing spring wheat productivity in the eastern Canadian Prairies: I. Yield, yield components, and lodging risk. Agronomy Journal, 114, 1731-1751.
Open access to the full article at: https://doi.org/10.1002/agj2.21044
Photo: Amy Delaquis