A Visual Guide to Soybean Growth Stages Understanding and being able to correctly identify the growth stages of soybean is important for making sound agronomic management decisions. This guide describes the growth stages starting with germination, progressing through the vegetative stages (V) and concluding with the reproductive stages (R). Coolbeans! Germination cotyledons Germination begins with the seed absorbing 50% of its weight in water, this is called imbibition 9 Imbibition is dependent on imbibition radicle soil temperature (optimum 60-70°F) and soil moisture (optimum 50%) 9 Imbibition requires good seed-to-soil contact hypocotyl 9 The radicle (or primary root) grows from the swollen seed and elongates downward 9 The hypocotyl begins elongation upward toward the soil surface, pulling the cotyledons along radicle VE growing point Vegetative Stage Emergence Cotyledons above the soil surface VE stage occurs approximately 5-14 days after planting depending upon the soil temperature, which can be influenced by planting date 9 Soil crusting and planting depth cotyledon (either too deep or too shallow) cotyledon can inhibit emergence 9 Planting too deep can also delay emergence; planting depth should be between ¾ to 1-½ inches main stem There are two methods used to determine the vegetative growth stages of soybean. Although they use different techniques, the Methods resulting growth stage determination is the same; it’s helpful to understand how both work and be familiar with the terminology. 1. Hybrid Method (P. Pedersen) Pedersen, Palle. 2009. Soybean growth and This method is commonly used in the field and grower publications; it counts development. Iowa State University Extension, the number of open trifoliolate leaves on the main stem. Ames, Iowa. 2. Fehr and Caviness Method Fehr, W.R., Caviness, C.E., 1977. Stages of soybean This method is used in academic settings and journal articles; it counts the development. Cooperative Extension Service, Agri- number of nodes on the main stem, beginning with the unifoliolate nodes, culture and Home Economics Experiment Station, that have or have had a fully developed leaf. A leaf is considered fully Iowa State University, Ames, Iowa. developed and the node is counted when the leaf at the node immediately above it is open. not open: open A leaf is considered leaf edges are touching Quick tips! open when the individual leaves are unrolled, and the leaf trifoliolate: edges are no longer a compoound touching. leaf with three leaflets A leaf is considered fully de veloped open fully developed: when the leaf at the leaf at the node node immediately above it is open above it is open. A node is the part of the stem where the leaf petiole develops. Leaf scars can be useful for locating unifoliolate nodes even if the leaves are lost or leaf node damaged. scar 1. Begin at the lowest portion of the stem above the soil surface. Feel for the first set of scars from the cotyledons. The scars will be opposite on the stem. 2. Above these are a second set of opposite scars that mark the unifoliolate leaf nodes. cotyledon scar cotyledon scar 3. All of the scars above the unifoliolate leaf detail nodes are singular and opposite on the stem. VC unifoliolate leaves Vegetative Stage Cotyledon Unifoliolate leaves unrolled sufficiently so the leaf edges are not touching unifoliolate nodes are counted as the 1st leaf node 9 Unifoliolate leaves are simple, consisting of a single leaf blade 9 Unifoliolate leaf nodes are opposite on the stem and are counted as the 1st leaf node cotyledon 9 The cotyledons are the first source of nutrients and energy prior to photosynthesis 9 Plants will not recover if damaged below cotyledons one open trifoliolate 3 easy steps — Fehr/Caviness method 1 1. Starting at the top of the plant, find the uppermost open trifolio- V1 late on the main stem and locate Vegetative Stage 1 leaf node 2 the corresponding node. 2. Move down the stem to the Hybrid method: next node. One open trifoliolate leaf 3. Count that node and all nodes node 1 below it on the main stem Fehr/Caviness method: st Fully developed leaves at including the 1 leaf node (unifoliolates nodes). unifoliolate nodes The number of nodes counted is 9 The 2nd leaf node and all nodes to follow the vegetative growth stage. are singular and alternate on the stem 9 Nitrogen fixing root nodules begin to form on the roots through infection by Fehr/Caviness method: Bradyrhizobium japonicum bacteria (introduced via inoculation or native For the plant pictured, leaf node 2 has the uppermost open trifoliolate, so the leaves at in the soil) leaf node 1 (the unifoliolate nodes) would be 9 Nitrogen fixation is necessary for considered fully developed; the plant is at V1. high yields 9 Assess stand count during this stage to determine if replanting is necessary see Think Twice Before Replanting Soybeans at http://www.coolbean.info/library/documents/SoybeanReplant_2014_FINAL.pdf or download the BeanCam app, links available at http://ipcm.wisc.edu/apps/beancam/ Each method uses a similar notation for the vegetative stages: Hybrid method: Vn ...............where n represents the number of open trifoliolates Good to know! Fehr/Caviness: Vn nth node ..where n represents the number of nodes on the main stem (beginning with the unifoliolate leaf nodes) that have or had a fully developed leaf V2 two open trifoliolates 2 Vegetative Stage 2 1 Hybrid method: Two open trifoliolates Fehr/Caviness method: Fully developed trifoliolate leaf at node above the unifoliolate nodes leaf node 3 leaf 9 Lateral roots are growing rapidly node 2 9 Active nitrogen fixation of the root nodules has most likely begun lateral roots leaf node 1 If weeds are present Fehr/Caviness method: during these stages, consider herbicide For the plant pictured, leaf application to node 3 has the uppermost open trifoliolate, so the trifo- minimize yield loss liolate at leaf node 2 (the node root nodule above the unifoliolate nodes) would be considered fully developed; the plant is at V2. three open trifoliolates V3 2 Vegetative Stage 3 3 Hybrid method: Three open trifoliolates leaf node 4 Fehr/Caviness method: 1 Three nodes on the main steam with leaf fully developed leaves beginning node 3 with the unifoliolate nodes Fehr/Caviness method: leaf node 2 For the plant pictured, leaf node 4 has the uppermost open trifoliolate, leaf so the trifoliolate at leaf node 3 would node 1 be considered fully developed. Count that node and the remaining nodes down the stem including the unifoliolate nodes. In this example, leaf nodes 3, 2 and 1 are counted; the plant is at V3. four open trifoliolates V4 3 Vegetative Stage 4 2 4 Hybrid method: Four open trifoliolates Fehr/Caviness method: Four nodes on the main stem with 1 fully developed leaves beginning 5 4 with the unifoliolate nodes Fehr/Caviness method: 3 9 For May planting dates in Wisconsin, For the plant pictured, leaf node 5 2 flower buds start to develop between has the uppermost open trifoliolate, V4-V6 so the trifoliolate at leaf node 4 would 1 be considered fully developed. 9 Plants can recover from 100% defoliation Count that node and the remaining at this stage with minimal risk of nodes down the stem including the yield loss unifoliolate nodes. In this example, leaf nodes 4, 3, 2 and 1 are counted; the plant is at V4. five open V5 trifoliolates 5 Vegetative Stage 5 Hybrid method: Five open trifoliolates 3 6 4 Fehr/Caviness method: Five nodes on the main stem with fully developed 5 leaves beginning with the unifoliolate nodes 4 9 Rapid dry weight accumulation begins 3 2 ~V5 100 2 90 Seeds 7000 1 Pods ) 1 Fehr/Caviness 80 -1 Stems 6000 Petioles method: 70 Leaves Fallen Petioles & Leaves 5000 For the plant pictured, 60 leaf node 6 has the 50 4000 uppermost open 40 3000 trifoliolate, so the tri- foliolate at leaf node 5 30 2000 Cumulative % of Total DM would be considered 20 TotalDMAccumulation (lbs a fully developed. 1000 10 Count that node 0 0 and the remaining 0 10 20 30 40 50 60 70 80 90 100 110 nodes down the stem Days after Emergence including the unifo- liolate nodes. In this example, leaf nodes V6, V7, etc., you get the picture. After V6, stages progress rapidly, usually every 3-5 days. 5, 4, 3, 2 and 1 are Soybean growth habit (whether a variety is determinate or indeterminate) will influence how counted; the plant is Keep going! many more V stages occur and if the V stages cease or continue after the R stages begin. at V5. The dominant growing point’s behavior differs Soybean growth habits with the two types of soybean growth habits. The dominant growing point on the main Indeterminate stem is also called the apical meristem or the stem apex. Continues new vegetative growth dominant even after flowering begins growing IMPORTANT NOTE! point on an The images in this guide generally R3 indeterminate represent indeterminate varieties variety grown in Wisconsin, keep in mind: Indeterminate varieties are typically 9 Rate of development can vary grown in the Central and Northern based on temperature, maturity U.S. (maturity groups 0.0~4.5) group, soil conditions, planting date and planting patterns 9 Differences may occur in time between stages, internode length, plant height and number of leaves Determinate Ceases new vegetative growth soon after flowering begins Determinate varieties are typically grown in the Southern U.S. 9 Determinate plants have a terminal (maturity groups 4.5~6.0) and in terminal node node with a long flowering raceme South America on the main stem, indicating the with a long flowering end of vegetative growth raceme on an R5 determinate variety 9 Flowers develop around the same time on determinate varieties; therefore pod and seed development are more uniform when compared to an indeterminate variety It is critical to accurately identify the correct growth stage for the entire field in order to make sound management decisions! GROWTH STAGING A FIELD Locate five areas within a field that represent the field Growth Stage 1 as a whole.