Determine lime and fertilizer needs by soil test. Soybean in rotation can make use of fertilizer applied to the previous crop; however, this does not eliminate the need for a sound fertility program. Maintaining a pH between 6.0 and 6.5 is critical. In the absence of a soil test, refer to the most recent soil test available for the field, and adjust rates according to values listed in Table 1.2-5 for soybeans. Apply fertilizer before seeding or band at least 2 inches to the side of seed at planting. Do NOT drill fertilizer with the seed or use “pop-up” fertilizer.
Soybean that has been properly inoculated with nitrogen-fixing bacteria rarely responds to nitrogen fertilization. If the previous year’s crop was not soybeans, inoculate seed with fresh, viable, nitrogen-fixing bacteria immediately before planting. Recent research results indicate a 70 percent chance for a 2.0 bushel-per-acre yield increase when inoculating seed planted into fields growing soybean every other year. If soybeans have not been grown previously in the field, consider using a triple inoculant rate or using two different inoculants (for example, pre-inoculated seed and a peat-based inoculant) to ensure adequate nodulation. Be especially careful to handle inoculants or pre-inoculated seed to avoid reducing viability by exposing them to hot or freezing temperatures. Monitor these first-year fields for nodulation; if nodulation is less than desired, consider applying nitrogen to these fields as soon as possible but before grain fill begins. Usually, about 75 pounds of nitrogen is adequate to maintain good yields on non-nodulated soybean fields. For more information, see Agronomy Facts 11: Inoculation of Forage and Grain Legumes.
If pH is below 6.0 and is not to be corrected with lime, apply molybdenum as a seed treatment at planting. This helps ensure proper nitrogen fixation and may slightly improve yields.