Management changes with double-cropped wheat, soybeans
Double cropping drastically reduces the elapsed time between successive crops and therefore can greatly increase the disease pressure for both crops. Where double cropping is practiced, the beneficial effects of crop rotation (weed, insect, and disease control) are totally negated.
There are two primary requirements for profitable multiple cropping:
- There must be adequate time for the production of a second crop.
- There must be adequate water to produce two crops, whether from stored soil moisture, rainfall, or irrigation.
Because the soybean crop is photoperiod sensitive and matures in response to day length, it is ideally suited for multiple cropping systems where planting dates for the second crop are later in the season and can be variable due to weather.
Currently, most double cropping systems depend solely on a combination of rainfall and stored soil moisture to supply adequate water for two crops. Irrigation can be used as a supplement for soils with a less than adequate water supplying capacity and/or inadequate rainfall. While irrigation can greatly increase the consistency of crop yields, it also increases the cost of production. If the top three inches of soil is dry when the second crop is planted, germination is greatly slowed until the receipt of adequate rainfall.
There also must be adequate soil moisture to enable the root system to grow into moist soil where water availability is more consistent. Because the water requirement is so large for double cropping, it is generally most successful on soils with large water supplying capacities that are sometimes referred to as "good corn soils."
Early planting of the second crop is essential for success, which requires harvest of the wheat as early as possible. Potential double crop soybean yield decreases by one bushel for each day that planting is delayed after June 20. Early wheat harvest can be accomplished by planting an early to mid-maturity wheat variety soon after the fly-free date in the fall and harvesting when the grain moisture decreases to 18% to 20% and then using air with or without supplemental heat to dry the grain. These actions combined can save several days that would normally be used to field-dry wheat to 10% to 14% moisture. If a grower wishes to maximize wheat production because of the high value of wheat relative to a following crop, early harvest may be less important.
Below-normal temperatures in June delay wheat maturation, which may require growers to reconsider planting the second crop. For someone considering double cropping, it may be necessary to have two wheat varieties differing in maturity available in the event that wheat maturation is delayed. In southern Ohio, soybean varieties with maturity ratings of 3.4 to 3.9 will usually mature before the first freezing temperature if planted in June. Other than selecting a variety that matures before the first freeze, variety selection is not as important for double cropping as it is for a full season crop. Ohio studies have shown that early planting and July-August rainfall have a much greater impact on double crop soybean yield than does variety.