Intensive wheat management to reduce lodging

Objectives:

• To determine the effect of the newest plant growth regulators (PGRs) on winter wheat performance and profitability, including lodging potential, grain yield and quality.

• To determine the impact of PGRs within an integrated approach to increase profitability, reduce lodging potential, increase grain yields and to maintain or increase grain quality.
• To determine the effect of various desiccants on date of soybean harvest maturity, soybean yield, and soybean quality in full- and long-season cultivars in two environments in southern Ontario.
• To determine wheat yield and farm profitability of advancing seeding dates in winter wheat using desiccants in various soybean maturities.

Impacts:

• This project provided independent validation of the efficacy of the newest plant growth regulators (PGRs) in terms of reducing lodging potential in winter wheat, and how these PGRs fit within an integrated approach for increasing wheat performance. The cross-Ontario dataset from this project will help advance intensive wheat management to a new level of profitability, encouraging growers to include wheat in their crop rotation.
• This study helped quantify the extent of yield reductions and harvest maturity advancements possible with desiccation treatments and can be used to inform farmer management decisions.

Scientific Summary:

Wheat brings tremendous value to Ontario agriculture by increasing corn and soybean yields, increasing soil organic matter (OM), facilitates the use of cover crops, reduces soil erosion, lowers GHG emissions, and increases whole-farm profitability. Despite these benefits, the wheat enterprise needs to be economically competitive with other crops to maintain acreage in Ontario. Lodging reduces crop yield, quality, and harvest efficiency. Moreover, with this fear, current nitrogen (N) rates are likely not at their optimized economic response when the risk or fear of lodging is factored into the rate decision. From previous work in Ontario, we know that N rates are not optimized without the application of a fungicide, and that the economic N rates are environment and cultivar specific. A similar systems approach is needed to reduce lodging potential with a better understanding of input responses and how they interact with the environment.

Thus, we proposed to develop effective 4R-based strategies for managing lodging risk, and to determine the fit of plant growth regulators (PGRs) within this approach, using combinations of cultivars, N rates, N timings (one vs. split), and N sources, with and without a PGR. We proposed two experiments at multiple locations across the province: one with a PGR-variety focus and the other a more integrated focus with wheat variety, N source, N rate, and split N application, with and without a PGR. Both experiments were “linked” with common treatments. These strategies need a 4R approach to reduce the amount of N in the soil that may be susceptible to leaching or denitrification before crop uptake. Moreover, the second split timing of N (GS32 +/-mid May) may be used to adjust N rates given a better prediction of crop demand (compared to only one application of total N at greenup).

In a second paired experiment, we wanted to see how soybean harvest could be hastened to facilitate timely winter wheat planting. The motivation of this experiment was two-fold: First, Ontario winter wheat yield potential is reduced if not planted during the optimal planting window. So, ensuring soybean harvest occurs before this optimal planting window has passed is important. Second, because farmers understand the importance of planting wheat during the optimal planting date window, they will often grow a shorter-season soybean variety than optimal. This facilitates earlier planting but comes at the cost of lower soybean yield potential (compared to planting a full-season variety adapted to the area). So, we wanted to see if farmers could profitably obtain higher soybean yields by planting a full-season variety, but then using a desiccant to facilitate earlier harvest to ensure winter wheat yield potential remained high. The project measured the effect of desiccant application timing and desiccant product on soybean yield and harvest maturity, in both full-season (adapted) and long-season soybean varieties.

PGR Results:

Experiment 1 (2021 and 2022):

In 2021, lodging was moderate to high at both Winchester and Arva, and low at Ridgetown in most of the winter wheat cultivars in the experiment. In 2022, lodging was moderate in some susceptible varieties at Winchester in 2022, but only low in both Arva and Ridgetown. One of the biggest factors for determining lodging potential is weather, which is a major contributor of variability across site-years. Nevertheless, site-specific variation in lodging was beneficial for the project and objectives, as crop responses across a range of conditions for lodging potential are important for assessing planting date effects and management, the use of PGRs, and how N management affects crop yield and quality. In general, at site-years with significant potential for lodging, the use of a PGR (Moddus or Manipulator) significantly increased yields over the untreated control (3-7 bu/ac yield increase) because less lodging occurred. This yield increase was pooled across plots with the higher N rates (150 and 200 kg N/ha). When the potential for lodging was high in susceptible varieties, PGRs significantly reduced lodging by an average of 20%.

Where and when the lodging potential was low, PGRs had no effect on yields, which contrasts with some company/sponsor data. In some scenarios, lodging was reduced with the application of a PGR, but the lodging was still unacceptable. PGRs reduced lodging, but overall lodging was very low at some sites.

While PGRs shortened stems, they increased stem density by 7% (grams per cm of stem), which compensated in terms of straw yield.

The data are being used for a MSc thesis to determine the physiological processes that affect lodging, and how PGRs affect those physiological responses of wheat. In short, PGRs tended to shorten stem internode along with a thickening of stem diameters and stem wall thicknesses between GS70 and GS85. Equations have been developed to predict lodging potential and the need for PGRs.

We have the data to help predict lodging potential of wheat to determine the value of applying a PGR, and to refine N management, although more site-years are required (and planned) to validate these results and to support updated field crop recommendations.

Experiment 2 (2021 and 2022):

The PGR effect on yield depended on the N rate and susceptibility of the cultivar.

We applied N in the following rates (kg N/ha): 0, 100, 150, 200, 250. In most site-years to date, the PGR increased yield significantly at N rates 150 kg N/ha and above, because lodging was reduced. At Ridgetown in 2021 and 2022, and Arva 2022, the PGR increased yield only at N rates of 200 and 250 kg N/ha. Clearly, the data show that lodging reduces yield and quality, but its management requires an integrated approach.

The highest wheat yields were produced with early planting dates. A planting date and wheat yield relationship was produced (a quadratic curve) using the data to assist growers in decisions around planting time.

Key Take-Aways from PGR Results:

Six site-years of data were collected for the PGR focus, and another 6 site-years for the planting date focus. In short, i) grain yield increases with N rate, but so does lodging risk, hence an integrated strategy to reduce lodging needs to be deployed; ii) PGRs reduce the risk of lodging but there is no evidence of yield benefits if lodging is not an issue, which contrasts with some data from PGR companies; iii) some cultivars have more lodging risk than others; more investigation is needed; iv) we recommend that the Ontario Cereal Crop Committee (OCCC) should increase N rates and adopt a PGR on intensively-managed plots to recommend a strategy based on wheat cultivar; v) it appears from our dataset that some cultivars may “react” negatively to a PGR; however, more data are needed (e.g., future work); vi) early planting dates tend to have higher yields, but the response to intensive management tends to be similar regardless of planting date.

We are not confident that a “minimum dataset” has yet been acquired that could predict future crop responses across varied weather conditions and cropping systems across Ontario. Any results from this study need to be taken with caution until a minimum dataset has been acquired, and until the results are vetted to the scientific community and validated on farm fields. That said, wheat is highly responsive to N, but the response depends on several factors. We have shown that the response to fertilizer N depends on whether a fungicide was applied (or if leaf diseases are controlled), and that this response also depends on the wheat cultivar. This project had a focus on planting date and lodging management.

• High wheat yields tend to increase lodging potential, so each need to be managed simultaneously.
• Lodged crops reduce yields (up to 20% lower yields in this study).
• Early planting increases yield – which is well known; however, this project showed that the wheat response to intensive management using higher rates of N and a PGR was similar across all planting dates (although more site-years of data are needed).
• Early planting increases the number of spikes per square meter, which increases lodging potential, thus would require a different N management and PGR strategy compared to late planting.
• An integrated strategy to reduce lodging needs to be deployed.
• PGRs reduce the risk of lodging but there is no evidence of yield benefits if lodging is not an issue.
• Some cultivars have more lodging risk than others. High yield environments, such as those created by early planting, should be planted with a cultivar with some lodging tolerance.
• Information on variety lodging risk can be determined through the OCCC; however, only a few OCCC locations are set up to produce a lodging potential to assess cultivar differences.
• N rates need to be determined for economical responses. Avoid excessive use of N, otherwise it will increase the risk of lodging and environmental losses.
• Some cultivars may “react” negatively to a PGR; however, more data are needed – (future work); consult seed company reps for more information.

Desiccant and Soybean Relative Maturity Results:

Experiment 3 (Effect of soybean variety maturity and desiccation management on soybean yield and time to harvest maturity):

The project was conducted at the Huron and Ridgetown research stations in south-western Ontario over three seasons (2020-2022). Two soybean maturity groups (MGs) were grown (3 varieties per maturity group): full-season adapted varieties, and longer-season varieties that take longer to mature (0.3-1.6 MG greater than the full-season variety). Four varieties were tested in each location-year, with the varieties themselves changing because Huron and Ridgetown are in different soybean MG zones (1.0 and 1.5, respectively). Three desiccant products were applied (diquat, saflufenacil and borax) along with an untreated control. Desiccants were applied at three timings based on soybean growth stage: R6.5 (prior to leaf drop), R7 (at leaf drop), R7.5 (mid-leaf drop).

Data collected included: time from planting to soybean growth stages R6.5. R7 and R7.5, date of desiccant application, date of harvest maturity (i.e., yellow stem), soybean grain yield, and soybean grain quality (test weight, oil, protein).

Soybean Harvest Maturity Results:

Diquat application at R6.5 had the largest and most consistent effect on advancing harvest maturity compared to untreated controls. On average, maturity was advanced by 6-10 days in the full-season MGs and 3-11 days in the long-season MGs. Diquat application at R7.0 had a smaller but still consistent effect on advancing harvest maturity. Other desiccants had a smaller and less consistent effects on harvest maturity, particularly borax. It is important to note that in 2 of 6 site-years, desiccation treatment had no effect on harvest maturity at all due to an early Fall frost that terminated the crop.

On average, long-season MGs reached maturity 3-15 days after adapted MG varieties, as we expected. However, when diquat was applied at R6.5, long-season MGs were often able to reach harvest maturity earlier or at the same time as untreated adapted MG soybeans. In other words, a farmer could plant a long-season MG, apply diquat at R6.5 and would be able to harvest soybeans at the same time or earlier than planting a full-season MG with no desiccant applied.

Grain Yield Results:

On average, yields were +4.9 bu/ac greater for the long-season MGs compared to adapted MGs. This was expected.

Applying diquat at R6.5 (the treatment with the largest effect on advancing harvest maturity) reduced yields relative to untreated controls in 2 out of 6 site-years (-2.5 bu/ac and -6.8 bu/ac). In the remaining 4 site-years, diquat applied at R6.5 reduced yields numerically but not significantly compared to the untreated control. Overall, the average yield reduction from applying diquat at R6.5 was -3.2 bu/ac (not significant).

One important comparison is between the untreated adapted MGs and the late-season MG with diquat applied at R6.5. In other words, to see if higher yields could be obtained by switching from an adapted to long-season MG while also using diquat at R6.5. On average (all six site-years), yields were +3.6 bu/ac greater with a long-season MG + diquat (R6.5) compared to a full-season MG (no desiccant). However, in two out of six site years, yields were reduced moving from an untreated full-season MG to a long-season MG with diquat applied (in one of those location-years, it was due to an early frost reducing yield of all long-season MG treatments).

Another important comparison is the adapted MG with diquat applied at R6.5 versus the untreated (control) adapted MG. Here, on average, diquat at 6.5 reduced yield by -1.5 bu/ac. Yields were reduced in every site-year. However, the increase in harvest maturity (up to 10 days, average = 5) from using diquat may still be advantageous despite the yield decrease.

Key Take-Aways from Desiccant and Soybean Relative Maturity Results:

• The most consistent desiccation treatment in terms of advancing harvest maturity was diquat applied at R6.5. Saflufenicil and borax, and diquat applied at later times, had smaller and much less consistent effects on harvest maturity relative to untreated controls. However, we must acknowledge that even with diquat at R6.5, there were two out of six site-years where desiccants had no effect at all. In these two site-years, an early fall frost negated any potential benefit of desiccation. Ignoring these two site-years, diquat applied at R6.5 advanced harvest maturity by an average of 7 days (averaged across all soybean varieties).
• Small yield reductions, not always significant, are to be expected when applying a desiccant at R6.5, even if this yield reduction was not always statistically significant.
• A farmer could increase yields by ~3.6 bu/ac by planting a longer-season MG variety and applying diquat at R6.5, and still reach harvest maturity at the same time or earlier, compared to an untreated adapted MG.
• Currently, farmers often plant a short-season soybean MG in fields they intend to plant winter wheat into, for the purpose of advancing harvest maturity. This helps with timely wheat planting but reduces soybean yield potential compared to planting an adapted MG. Our results suggest that planting an adapted MG and desiccating with diquat at R6.5 may result in greater yields and similar/earlier harvest maturity compared to planting an untreated short-season MG variety.
• When deciding whether to apply a desiccant, the farmer must balance the cost of the desiccation application, the possible reduction in yield, and the benefits of earlier harvest. This study has helped quantify the extent of yield reductions and harvest maturity advancements possible with desiccation treatments and can be used to inform management decisions going forward.

External Funding Partners:

This project was funded in part by the Governments of Canada and Ontario through the Canadian Agricultural Partnership, a five-year (2018-2023), federal-provincial- territorial initiative. It was also funded in part by the Ontario Agri-Food Innovation Alliance, a collaboration between the Government of Ontario and the University of Guelph.

Syngenta

Belchim

Project Related Publications:

None.