Conditions That Impact Soybean Germination and Emergence

Conditions that Impact Soybean Germination and Emergence  The sequence of events during germination begins with imbibition (absorbing water) followed by the development of the radicle (primary root) and emergence of the cotyledons (seed leaves).  Planting into a moist seedbed with good seed-to-soil contact is important for optimal germination.  Dry or flooded soils, cool temperatures, and lack of oxygen in soils are conditions that can hinder soybean germination and emergence.

Soybean Germination The cotyledons are a temporary source of stored food for the seedling. Shortly after emergence, they open and turn green Soybean seed germination is referred to as “epigeal” because because of their exposure to light and start making additional food storage structures (cotyledons) are pulled above the soil food through photosynthesis. As the cotyledons open, the surface. In contrast, corn germination is considered “hypogeal” epicotyl is revealed (Figure 3). The epicotyl contains small where the storage structure remains below the surface leaves, buds, and the main growing point. The cotyledons drop following germination. off shortly after the first set of true leaves is formed. After planting, a soybean seed will start to absorb or imbibe water and swell, and as a result, change its moisture content from less than 13% to almost 50% in several hours. Within one or two days under favorable temperatures, the first root (radicle) of the swollen seed emerges through the seed coat (Figure 1) and grows downward to develop the primary root. Lateral roots quickly emerge from the radicle as it elongates and root hairs grow from the radicle and the lateral roots. Root hairs are barely visible and should not be confused with later developing and easily seen branch roots. The root hairs become the main Seed hilum absorbing structures. Five to ten days after planting, the new seedling emerges from below the soil surface. The hypocotyl begins to elongate and Figure 1. (Left) Imbibition of a treated seed causes the radicle forms a hook that pushes through the soil surface, pulling the (red arrow) to emerge through the seed coat (yellow arrow). (Right) cotyledons upward (Figures 2 & 3). The hypocotyl can be easily Seed hilum or scar where the seed was attached to the plant ovary broken if the soil surface is too hard or crusted to push through. within the pod. Seedlings usually die if the hypocotyl is broken.

Figure 2. Hooked hypocotyl and cotyledons Figure 3. Cotyledons (yellow arrow) Figure 4. Soybean seedlings with fully expanded breaking through the soil surface. open to expose epicotyl (red arrow). cotyledons (green arrow), unifoliate leaves, and growing point above the soil surface. Conditions that Impact Soybean Germination and Emergence

Conditions that Affect Germination and Table 1. Soybean Seedling Structures Emergence Structure Function/Characteristic Moisture. Planting into a moist seedbed with good seed-to-soil contact is necessary as moisture needs to move into the seed for germination to occur. If irrigation is required for adequate Testa (Figure 1) Seed coat soil moisture, it should be applied ahead of soybean planting and not immediately after planting. Planting into dry soil with Seed hilum or scar Location where the seed was attached rainfall or irrigation occurring too soon after can result in soil (Figure 1) to the plant ovary within the pod crusting and poor soybean emergence. Radicle First part of the embryo to penetrate Soil Conditions. Soil crusting can delay or prevent seedling (Figure 1) the seed coat; develops into main root emergence and cause soybean hypocotyls to become swollen or broken when trying to push through the crust. Fields with Tissue between cotyledons and Hypocotyl fine-textured soils, low organic matter, and little surface residue radicle that becomes the stem of the (Figure 2) can be vulnerable to crusting, especially where excessive tillage plant after germination has taken place. Temperature. Soybean seed can begin to germinate when soil Cotyledons First leaves to appear; serve as food temperatures are less than 55° F; however, germination is likely (Figures 2, 3, & 4) storage structures to be slow until soil temperatures warm to the upper 70s. Cold Stem area above the cotyledons that soil temperatures can cause seeds to remain dormant, Epicotyl consists of a stem, two primary increasing their vulnerability to seed and seedling diseases and (Figure 3) feeding by insects and wildlife. When soil temperatures are leaves, and a terminal bud between 70º F and 90º F, seedling emergence should occur in less than a week. Soil temperatures above 95º F can also Sources: cause poor soybean germination and emergence resulting in 1 Soybean as a crop. Modern corn and soybean production. MCSP, http://www.mcsp- reduced stands. pubs.com. Other sources: Hoeft, R.G., Nafziger, E.D., Johnson, R.R., and Aldrich, S.A. 2000. Modern corn and soybean production. First edition. MCSP Publications. Champaign, IL. Pedersen, P. Oxygen. Because seed respiration increases during the 2007. Soybean growth stages. Soybean growth & development. PM 1945. Soybean germination process, saturated, flooded, and compacted soils Extension and Research Program. Iowa State University. http://extension.agron.iastate.edu. Pedersen, P. Soybean planting date. Iowa State University. can reduce germination and emergence due to the lack of http://extension.agron.iastate.edu oxygen. Soil pore spaces filled with water reduce the amount Web sources verified: 4/16/15 of oxygen available for seed respiration. Compacted soil reduces the availability of water and oxygen required for For additional agronomic information, please contact your local seed representative. germination, root and plant growth, and nutrient uptake. Developed in partnership with Technology, Development, & Agronomy by Monsanto.

Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. ©2015 Monsanto Company. 140513060107 051314SMK