How Shade Tolerant Are Soybeans?

Growing Conditions

• Considered a broadleaf summer annual, soybeans require warm soil rich in nutrients, especially nitrogen. Soybeans grow best in soil temperatures of 55 to 60 degrees F. Although soybean seeds require moist soil to germinate, too wet a soil can cause seeds to rot. Good drainage is essential. Soybeans have a short planting window, as they do not tolerate frost but also suffer from wilt and bacterial disease caused by summer heat.

Shade Tolerance

• Plants require light to make the energy needed to fuel growth. The process of converting light energy, water, air and green pigment to a sugar that creates chemical energy is called photosynthesis. This process occurs in all plant leaves. Because of the need for light for photosynthesis to occur, plants do not prefer shade. However, some plant species need less light to grow. Shade tolerance is the capacity of a plant to survive and even thrive under these shaded conditions.

Photosynthesis

• While photosynthesis is the process that defines how plants make food, respiration is how plants consume food. The more shade tolerant a plant is, the better it balances the photosynthesis/respiration process under low light levels. Shade-tolerant plants use solar energy more efficiently to produce fuel without burning, or consuming, it all in the process. They thrive without a lot of sun and outgrow less shade-tolerant species.

Shade Tolerance of Soybeans

• Soybeans are not only shade tolerant but actually thrive in the shade. Sensitive to the length of daylight hours, soybeans do not flower unless they experience 10 or more consecutive hours of darkness. Leaves thicken as shade increases. Conversely, if shade is minimal and sunlight is too intense, the soybean cell's metabolism causes increased respiration, or energy use. With increased respiration, photo oxidation takes place, causing the destruction of chlorophyll, which typically results in leaf breakage.

Growing Cycle

• Due to needing short growing days yet warm soil, soybeans should be planted as soon as possible after the last frost but no later than early June. With longer summer days and lack of shade, soybean seeds do not mature and yields, decrease. Once the shorter fall days occur, leaves turn yellow and brown from lack of sunlight and fall off. Then the matured soybean pods are exposed and ready for harvest.