In recent years double cropping soybeans has become more common. In the past, double cropping was mainly attempted after winter barley or pea harvest in July. Now, double cropping after winter wheat has become more common in southwestern Ontario. Double cropping can be successful if soybeans are seeded early enough with adequate soil moisture for germination, and they mature before a killing frost. Choosing a short season variety (low MG) for a given area helps the crop to properly mature in the fall. In southwestern Ontario, growers have been able to achieve a 2.7 t/ha (40 bu/acre) crop if planting before July 10th, as long as the weather cooperates. However, yield potential drops approximately 67 kg/ha/day (1 bu/acre/day) after July 1st, so realistic yield expectations are important when budgeting double crop soybeans. If seeding after July 10th, the chance of success reduces drastically. Areas with more than 3000 Crop Heat Units (CHUs) have a greater likelihood of success, although areas above 2800 CHUs have also been successful. Areas with less than 2800 CHUs have a much lower success rate. There is no crop insurance for double cropped soybeans.
Wheat is frequently harvested early by producers who have success with double cropping, even if drying is required. The following management tips will increase the chances of a successful double crop:
- Due to the need to control volunteer wheat, glyphosate-tolerant varieties are better suited for double cropping. Conditions are also drier in the summer reducing herbicide efficacy.
- Plant immediately after a timely cereal or pea harvest. Every day counts. Double cropping after July 10th is not usually successful.
- Do not till the field so moisture is retained, and costs are reduced. At harvest, leave approximately 20 cm (8 in.) of cereal stubble to promote soybean stem elongation and higher pod set.
- Plant 1 cm (0.5 in.) into moisture, but no deeper than 7.5 cm (3 in.). If the soil is extremely dry it may be better to wait for a rain. Many double crop failures can be attributed to seeds being planted into very dry conditions.
- Select tall, small seeded varieties that are at least 1.0 MG lower than full season (adapted) for that area. It may be necessary to select extremely short season varieties to ensure they have time to finish before a killing frost.
- Plant in narrow rows, using high seeding rates (618,000 seeds/ha or 250,000 seeds/acre) or higher.