North Carolina farmers plant soybeans in all 100 counties in the state from the mountains to the sea. At 1.6 million acres in an average year, soybeans have the biggest footprint of any crop in the state. In a good year, the crop is worth as much as $800 million to farmers. Because soybeans work well in rotation with other crops like tobacco and can be planted in the same field in the same year following the winter wheat crop, it is a very popular crop with farmers.
The optimum planting period for soybeans in North Carolina is from May 1 to June 10, but soybean planting can occur sometime in April until July 1 in the state. Seed should not be planted until soil temperatures are above 55 to 60O F. Because soybeans are photoperiod sensitive, planting date directly impacts the number of days to flowering or the amount of time available for vegetative growth, which in turn directly affects plant yields. Planting beyond the optimum date may result in reduced yields. The goal should be to get the middles lapped and plants to a height of three feet before reproductive growth begins. The later the planting date, the greater the chance yields will be reduced.
Soybean growth is known to be adversely affected by low soil pH. Yields are best when pH is near 6.0 in mineral soils. It is important to fertilize soybean crop based on soil samples.
There is a wide range of row spacings that have been used successfully in soybeans production. Often, row spacing decisions are made based on what equipment is already available. In a series of on-farm tests in North Carolina, soybeans in 10-inch to 20-inch rows yielded 3 bu/A higher when planted earlier, and 4 bu/A higher when planted later, than soybeans on 36 to 40 inch rows. There was little difference in yield between the 10-inch and the 20-inch rows.
The earlier you can plant group fours and fives the better. NCSU recommends that a group 4 be planted no later than end of May. NCSU recommends that group five not be planted past the 10-15 of June. Planting group 7 varieties can be planted at any time. It is important to remember that once group four and five soybean varieties reach maturity and are ready for harvest that they are harvested timely to prevent yield loss and crop damage.
Soybean yield is relatively insensitive to plant population. Percentage wise, the yield plateau between too many and too few is wider for soybeans than for any other crop.
Because soybeans have the unique ability to compensate, a wide range of seeding rates is acceptable. Final stands as low as 50,000 plants for May planted beans, 75,000 plants for June planted beans and 100,000 plants for July planted beans can produce reasonable yields if plants are evenly distributed.
With that being said, the standard recommendation for our area is 125000 final plant germination. With 90 percent germination you set to plant around 138,000 seeds per acre. There have been many studies on soybean plant population. Currently, research being conducted to see which plant population and planting date match up the best.
For more information on soybeans, contact Lance Grimes at 252-789-4370 or visit these websites:
NC State Extension Portal Page: https://soybeans.ces.ncsu.edu/
North Carolina Soybean Producer Association: https://ncsoy.org/