Double Crop Soybean Management

As we are planting our full season soybeans, it is also time to start planning for double crop soybeans. Historically double crop soybeans after winter wheat were not encouraged north of I-70. In recent years reports are growing of successful double crop soybeans as far north as U.S. Hwy 30.  While many are familiar with some of the basic management suggestions for double crop beans, the fertility implications of the beans are often overlooked.

The key to double crop soybean yields is to get the crop off to a strong start as early as possible. To do this cut your wheat as early as possible. If there is the ability to dry the grain or grain moisture discounts are not prohibitive, consider cutting wheat at a higher grain moisture. Baling the straw is often a question of debate and most often is based on the ability to manage/handle residue at planting. Uniform seed depth and seed to soil contact is much more important in double crop beans due to the reduced likelihood of steady rains to overcome planting errors. In the event of heavy rain near double crop planting time, be sure to have good soil conditions for planting. A day or 2 earlier planting will not overcome the negative impacts of planting too wet.  There have been reports of increased yield by cutting the wheat low when baling, the shorter straw reduces shading of small soybeans and reduces water transpiration rates out of the soil through the standing straw.

Large acres of double crop soybeans can be challenging to harvest as you move north. Planting soybean varieties near the top end of the suitable maturity is advisable to maximize yield. This means the soybeans will be harvested late, often in the late fall when drying conditions are not conducive to soybean harvesting. Focus on those fields with better fertility. Good phosphorus levels will promote good root development to help access moisture and nutrients in the drier months of the summer. Good potassium levels will help the soybean plant better utilize water in the hot/dry summer months.

Fertility is often the most overlooked aspect of double crop beans. While often the focus is on the nutrient removal of the wheat straw, a strong double crop soybean crop will remove a significant amount of potassium. Be sure to take the straw and the double crop beans into the crop removal consideration when determining nutrient recommendations.

Figure 1. Nutrient removal amounts and associated cost when baling straw.

Figure 1 shows some actual nutrient removal for straw harvest in Northeast Indiana and Northwest Ohio. Actual crop removal values from lab data in 2023 was substantially lower than book values. The cost per ton of straw using early spring 2024 fertilizer prices show a range in nutrient values of $14 to $21 per ton of straw. Potassium was the nutrient removed in the greatest amount, 14 to 25 pounds of K20 per ton. Book values for wheat straw are 3.7#/ton of P2O5, and 29#/ton of K20.

Figure 2. Pounds of nutrient removed per acre in relation to double crop soybean yields.

Figure 2 shows the nutrient removal from double from soybeans. As yields increase the nutrient removal becomes quite significant. The baling of straw and harvest of a good double crop soybean can lead to significant movements in soil test potassium levels if not replaced.

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