Growth and Development

OVERVIEW

The soybean is a dicotyledonous plant that exhibits epigeal (above the surface) emergence. During germination, the cotyledons are pushed through the soil to the surface by an elongating hypocotyl. Because of the energy required to push the large cotyledons through heavy soils, soybeans generally emerge best if they are planted no deeper than 2 inches. After emergence, the green cotyledons open and supply the developing leaves with stored energy, while capturing a small amount of light energy.

The first leaves to develop are the unifoliolate leaves. Two of these “single” leaves appear directly opposite one another above the cotyledons. All subsequent leaves are trifoliolates comprised of 3 leaflets.

GROWTH STAGES

Soybean development is characterized by two distinct growth phases. The first is the vegetative stages (V) that cover development from emergence through flowering (Table 1). The second is the reproductive ( R ) stages from flowering through maturation (Table 2). Plant stages are determined by classifying leaf, flower, pod, and or seed development. Staging also requires node identification. A node is the part of the stem where a leaf is (or has been) attached. A leaf is considered fully developed when the leaf at the node directly above it (the next younger leaf) has expanded enough so that the two lateral edges on each of the leaflets have partially unrolled and are no longer touching.

Table 1. Vegetative stages

Stage	Description
VE	Emergence – Cotyledons above the soil surface
VC	Cotyledon – Unifoliolate leaves unrolled sufficiently so that the leaf edges are not touching
V1	First-node – Fully developed leaves at unifoliolate node
V(n)	nth-node – Here, the "n" represents the number of nodes on the main stem with fully developed leaves beginning with the unifoliolate leaves.
From Fehr and Caviness

Table 2. Reproductive stages

Stage	Description
R1	Beginning bloom – One open flower at any node on the main stem
R2	Full bloom – Open flower at one of the two uppermost nodes on the main stem with a fully developed flower
R3	Beginning pod – Pod 3/16" long at one of the four uppermost nodes on the main stem with a fully developed leaf
R4	Full pod – Pod 3/4" long at one of the four uppermost nodes on the main stem with a fully developed leaf
R5	Beginning seed – Seed 1/8" long in a pod at one of the four uppermost nodes on the main stem with a fully developed leaf
R6	Full seed – Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf
R7	Beginning maturity – One normal pod on the main stem that has reached its mature pod color
R8	Full maturity – Ninety-five percent of the pods have reached their mature pod color. Five to ten days of drying weather are required after R8 for the soybean moisture levels to be reduced to less than 15 percent
From Fehr and Caviness

Table 3. Number of days between stages

Stages	Average # of days	Range in # of days
Planing to VE	10	5-15
VE to VC	5	3-10
VC to V1	5	3-10
V1 to V2	5	3-10
V2 to V3	5	3-10
V3 to V4	5	3-8
V4 to V5	5	3-8
beyond V5	3	2-5

R1 to R2	3	0-7
R2 to R3	10	5-15
R3 to R4	9	5-15
R4 to R5	9	4-26
R5 to R6	15	11-20
R6 to R7	18	9-30
R7 to R8	9	7-18
From Fehr and Caviness

Changes in environment, such as temperature and rainfall, can greatly alter the height of soybeans without a large effect on early reproductive growth stages such as flowering. Post-emergence herbicides are often labeled for application times that are dependent on soybean growth stages. To avoid injury, it is therefore very important to identify soybean development by growth stage rather than by their height, or the date they fill the rows.

Seth Naeve
Department of Agronomy
University of Minnesota Extension
(612)-625-4298
naeve002@umn.edu

URL: http://www.soybeans.umn.edu/cropgrowth/index.htm

Last Modified 3/25/11 2:10 PM
efans@umn.edu