In Arkansas, the soybean crop has the widest planting window compared to the other agronomic crops grown in the state. The standard recommendation for planting soybean varieties in Arkansas is between April 15 to June 30. Planting during the conventional time period (early May to early June) usually provides for rapid seed germination and emergence.
Soybean plants are sensitive to the photoperiod, or length of daylight (more specifically the number of hours of darkness). Thus, soybean plants can be especially affected by planting date since it impacts the number of days to flowering, and amount of time available for vegetative plant growth and plant development, which all are necessary for good yields. Planting beyond the optimum date will cause yields to be reduced. Planting too late can reduce yields because of poor stands due to excessively hot soil temperatures or because day lengths are too short. Short day length may result in plants flowering early and having reduced vegetative growth.
Research findings suggest that planting after June 15 results in a 1 to 2 percent yield loss per day, with the yield loss potential increasing to 2 to 3 percent per day after July 1 under moisture limiting conditions. Some of the yield loss associated with late planting can be minimized by changes in variety, variety growth habits, herbicide selection, increasing the plant population and decreasing the row spacing to 20 inches or less. Planting after July 15 is not recommended due to a greatly shortened growing season although some late MG IV and MG V varieties usually have enough time to produce mature seed before a fall frost if emerged by August 1. Plant height and grain yields will be greatly reduced in July plantings.