2016 was a year of extremes for Ontario soybean growers. Incredibly dry conditions in some regions resulted in poor yields or total crop failures in the most extreme cases. In contrast, a dry spring with few diseases, followed by timely rainfall in August resulted in amazingly high yields in parts of southwestern Ontario. Soybean yields are notoriously difficult to predict before harvest so much of the industry was pleasantly surprised at these good yields considering the growing season. Field averages of over 70 bu/ac were reported and yield monitors pushed over 100 bu/ac in the best part of some fields. Current estimates have the provincial average for 2016 at 44.8 bu/ac (with 56 per cent of the reports in from insured growers). This is slightly above the 10 year average of 43.9 bu/ac for those growers. The five year average for the province is 46.6 bu/ac. Soybeans are by far the largest field crop grown in the province with 2.715 million acres seeded in 2016. This was the third largest soybean crop in history. 2014 was the largest at 3.06 million and 2015 had 2.90 million acres.
Higher yields result in greater nutrient removal. Although soybeans take up almost twice as much potassium (K) as phosphorus, both nutrients are essential for soybeans. Factors that limit root growth such as dry conditions and sidewall compaction will reduce uptake. Under dry conditions, roots are unable to take up K from the soil even if soil K levels are sufficient. A soil test is the only reliable way to know if a field is truly low in K or just showing stress-induced potash deficiencies. It’s also important to note that K deficiency symptoms may be an indication of soybean cyst nematode (SCN) feeding on the roots. When taking soil samples, ask the lab to also test for SCN. A spring or fall application with incorporation work equally well to feed soybeans if soil tests warrant fertilizer.
The micronutrient manganese (Mn) is also critical for soybeans. Large parts of Ontario’s main soybean growing areas are deficient in Mn. Symptoms of Mn deficiency is interveinal chlorosis (yellowing). One of the most significant factors affecting the availability of Mn is the soil pH. As soil pH increases, less Mn is available to the plant. Deficiencies may occur on eroded knolls where the pH is higher than the rest of the field. The deficiency is most common on poorly-drained soils, especially on clays and silt loams. High organic matter also ties up Mn. Since only small amounts of Mn are required by the plant, a foliar application of Mn works well to rectify the deficiency. In severe cases, a spray application can provide a five or more bu/ac yield response.
Seedcorn maggot was more of a problem this spring than usual. Seedcorn maggots feed on germinating corn and soybean seeds and young seedlings. Damage can range from minor feeding which delays emergence to seed death. Seedlings that do survive are often severely weakened and may not fully recover. Seedcorn maggot numbers are impossible to predict but a mild winter likely increased populations in the spring of 2016. Maggot feeding results in hallowed out seed with small dark channeling. Flies are attracted to the odour of decaying organic matter that has recently been incorporated, such as freshly tilled soils, decaying plant residue, lightly tilled cover crops, and manured fields. The eggs are laid in moist soil and once hatched begin to feed on germinating seeds. For growers that consistently experience seedcorn maggot damage, an insecticide seed treatment is the only reliable control option. It’s also important to note that treated seed may not give complete protection under extreme insect pressure so higher seeding rates should also be used.
In dry years, some pests proliferate quickly. Spider mite damage was widespread this August. Mites feed on individual plant cells from the underside of leaves leaving stipples. Severe stippling causes yellowing, curling and bronzing of leaves. Spider mites usually start on the edge of the field but wind can carry them to any part of the field. From the road these pockets may look like moisture stress. Fields that are close to neighboring winter wheat stubble, hay fields and no-till fields are more at risk. Foliar insecticide applications were necessary on significant aces this year.
Double cropped soybeans
A number of growers were able to achieve 35 to 40 bu/ac this year, when seeding after winter wheat harvest. One of the reasons double copping is becoming more successful now than 20 years ago is due to higher yielding short season varieties. Plant breeding efforts for northern climates, especially western Canada have resulted in better short season varieties that can be seeded later in the growing season. Fields planted after July 15th or fields that remained extremely dry throughout the growing season were generally not successful.
Soybean variety selection continues to be one of the most important management decisions a grower can make to achieve high yield. The Ontario Soybean and Canola committee conducts performance trials each year across the province. Results from these trials can be found at gosoy.ca. Within a single test yield differences of over 10 bu/ac between varieties are not uncommon. Longer maturing varieties yield significantly more than shorter maturing varieties in most regions. Generally, longer maturing varieties yield 0.4 to 1.0 bu/ac more for each day they take longer to mature in the fall. For fields not intended for winter wheat seeding selecting a longer season variety is a cost effective way to increase yields.