Soybeans are a globally important agricultural commodity, cultivated for their oil and protein content. The final size of a mature soybean plant is highly variable, making a single, definitive measurement difficult. This wide range results from the plant’s genetic makeup interacting with its environment throughout the growing season. Understanding soybean height requires examining its typical range, influencing factors, and growth timing.
Standard Measurements and Typical Height Range
Fully mature soybean plants generally reach a height between 20 and 50 inches (0.5 to 1.3 meters). Agronomic professionals typically measure this height from the soil line up to the highest point of the main stem, excluding the highest leaves or pods. The standard expected height range for a healthy crop is often cited as 2 to 4 feet tall. This measurement reflects the plant’s final stature just before harvest when the stem has completed its elongation.
The total height is a function of the number of nodes developed on the main stem and the length of the internodes between them. The number of nodes is largely determined by the variety’s genetics and the duration of the vegetative growth period. Longer internodes, which increase the overall height, are often a response to environmental pressures like high planting density.
Environmental and Genetic Factors Affecting Stature
The most significant factors determining a soybean’s final height are its genetics, defined by its maturity group, and management practices like planting density. Soybeans possess two main growth habits: determinate and indeterminate. Indeterminate varieties, common in northern latitudes, continue to develop new nodes and increase in height even after flowering begins. Conversely, southern varieties are typically determinate, meaning vegetative stem growth largely ceases once the plant initiates the flowering stage.
Planting density directly impacts height through competition for sunlight. When soybeans are planted at high densities, they are forced to grow taller and thinner to outcompete neighboring plants for available light. This phenomenon, known as etiolation, results in increased height but often leads to reduced branching and fewer pods per plant. Plants grown at lower densities tend to be shorter, with a bushier structure and more side branches.
Environmental conditions such as moisture and temperature also limit a plant’s height potential. Drought or poor soil fertility generally restrict growth, resulting in a shorter final stature. Cool temperatures early in the season can limit the duration of vegetative growth before the plant switches to reproductive development. Optimal soil moisture and warm conditions allow the plant to maximize node count and internode length, enabling it to reach the upper end of its genetic height range.
Height Progression Through Growth Stages
Soybean growth is divided into vegetative (V) stages and reproductive (R) stages, and height accrual is concentrated primarily in the V stages. Vegetative growth begins with emergence and involves the rapid development of new nodes on the main stem. A new vegetative stage, marked by the appearance of a new fully developed trifoliate leaf, can occur every three to five days during this phase.
This period of rapid stem elongation and node addition establishes the majority of the plant’s final height. For indeterminate varieties, height accumulation continues into the early reproductive stages, as vegetative growth and flowering occur simultaneously. These varieties may continue to elongate their stems for roughly a month after they first begin to flower at the R1 stage.
Once the plant enters the reproductive phase (R1), the rate of height increase slows down considerably. Stem elongation typically ceases entirely around the R5 stage, when the seeds are beginning to fill the pod cavity. Understanding this progression is important for management, as it defines the window for applications like herbicides and helps gauge the plant’s susceptibility to lodging, or falling over, under high-wind conditions.