Where soils have been too wet to plant, soybean planting may be delayed until later than planned. Also, where young soybean stands have been devastated by hailstorms, drowning, or some other factor, producers may be thinking about replanting. In either case, with later-than-optimal planting dates, should producers make any changes in management strategies? For example, should a shorter-season variety be substituted or should seeding rates be adjusted as we move into late-June planting dates?
The following is adapted from the variety selection section of the Soybean Production Handbook, C-449: http://www.oznet.ksu.edu/library/crpsl2/samplers/c449.asp/
As planting is delayed, the situation begins to resemble double-crop soybean production. The soybean crop following wheat is usually planted 2 to 6 weeks later than the optimum date for highest yields. Since planting is delayed, often until the end of June or early July, one is tempted to switch to a shorter-season variety to ensure the crop will mature before frost.
While planting a variety that is too late in maturity may increase the likelihood of frost damage, switching to a substantially earlier maturing variety should be resisted. This is for two reasons.
* First, early-maturing varieties planted late in the season will usually have limited vegetative development, short stature, and low yield potential.
* Second, any given variety will have fewer days to flowering, pod development, and maturity when planted late compared to earlier planting dates.
As planting dates get later into June, day length has begun or will soon begin to shorten and nights will start getting longer. This causes plant development to speed up. Consequently, there is not a one-for-one relationship between the number of days difference in planting dates and the number of days delay in maturity. As a general rule, for every three days delay in planting, maturity is delayed by only one day.
Since soybean development is hastened with later planting, the highest yields in a late-planted or double-cropped system are often achieved by using the same variety or one very similar in maturity as what typically is used in full-season production. Sometimes a slightly later maturity variety will do better with later planting because it produces a larger plant before initiating flowering.
Other management practices can be affected by late planting, however. Because late planting shortens the period for vegetative growth and reduces canopy development, increasing the seeding rate alone or in combination with narrow row spacing can help the crop compensate by providing the opportunity to produce more pods in the canopy.
Seeding rates can be increased by 30 to 50 percent in high-rainfall environments if planting is delayed until late June or July. Although past research has demonstrated no consistent benefit for narrow row spacing (less than 30 inches) in Kansas, narrow rows may have an advantage in late plantings in the eastern half of the state.
Another reason for increasing the seeding rate if shifting to narrow rows relates to height of the bottom pods. Within-row plant spacing is greater in narrow rows at a given seeding rate, often causing the lowest pods to be set lower than in wide rows. Increasing the seeding rate in narrow rows decreases the within-row plant spacing and should raise the height of the lowest pods making harvest a bit easier.