Soybean

Glycine max

1. Identification and origin

Soybean [Glycine max (L.) Merr.] is an annual legume of the Fabaceae family, cultivated mainly for its grains rich in protein and oil. The species was domesticated in East Asia, with a probable origin in China, and spread globally throughout the 20th century, becoming one of the most important crops in the world in terms of cultivated area and economic value.

2. Economic importance

Soybean is one of the world's main sources of plant protein and edible oil, being fundamental for the production of animal feed, processed foods, biofuels and industrial products. Soybean meal is the main protein ingredient in animal feed, especially for swine and poultry. The oil is widely used in the food and chemical industries. The crop also plays a relevant agronomic role owing to its capacity for biological nitrogen fixation, contributing to soil fertility in crop rotations.

3. Botanical characterisation

Soybean is an annual plant of variable size (0.5–1.5 m), with an erect or semi-erect, pubescent stem. The leaves are trifoliate, alternate, with ovate to elliptic leaflets. The flowers are small, white to violet in colour, grouped in axillary inflorescences. The pods are pubescent, containing 1 to 4 spherical to ellipsoidal seeds, with great variability of colour (yellow, brown, black). The root system is taprooted, with abundant nodules formed by rhizobia of the genus Bradyrhizobium, responsible for atmospheric nitrogen fixation.

4. Edaphoclimatic requirements

Soybean adapts to temperate and subtropical climates, with optimal temperatures between 20 and 30 °C. It is sensitive to frost, especially in the early stages. It prefers well-drained soils of medium texture, with a pH between 6.0 and 7.0. The crop requires adequate moisture during flowering and pod filling, being vulnerable to water deficits in these phases. Inoculation with efficient strains of Bradyrhizobium japonicum is essential in soils where the crop is not traditional.

5. Main pests

• Caterpillars (Spodoptera frugiperda, Helicoverpa armigera) — defoliation and damage to pods
• Stink bugs (Nezara viridula, Piezodorus guildinii) — sap sucking, pod abortion and reduction of grain quality
• Whitefly (Bemisia tabaci) — sap sucking and transmission of viruses
• Mites (Tetranychus urticae) — chlorosis and reduced photosynthesis
• Thrips (Frankliniella occidentalis) — damage to young leaves and flowers, which can reduce fruit set
• Nematodes (Meloidogyne spp.) — root galls and reduced vigour

6. Main diseases

• Soybean rust (Phakopsora pachyrhizi) — leaf pustules and early defoliation
• Stem canker (Diaporthe phaseolorum) — necrosis and death of plants
• Downy mildew (Peronospora manshurica) — chlorotic spots and sporulation on the lower surface
• Root rots (Rhizoctonia solani, Fusarium spp., Phytophthora sojae) — death of seedlings and decline
• Soybean mosaic virus (SMV) — mosaics, deformations and reduction of yield

7. General crop management

Soybean management is based on the selection of cultivars adapted to the photoperiod and local conditions, on adequate inoculation with Bradyrhizobium and on establishment in well-drained soils. Crop rotation is essential to reduce the pressure of root diseases and nematodes. The monitoring of stink bugs and rust is critical, especially in humid and warm environments. Fertilisation should be balanced, with attention to phosphorus and potassium, since the crop fixes atmospheric nitrogen. Harvesting should be carried out when the pods reach physiological maturity and the grain moisture content is adequate for storage.

Bibliographic references

• EPPO Global Database – Glycine max
• CABI – Crop Protection Compendium – Glycine max
• Hartman, G. L., et al. (2011). Compendium of Soybean Diseases and Pests. APS Press.
• Sinclair, T. R., & Horie, T. (1989). Leaf nitrogen, photosynthesis, and crop radiation use efficiency. Crop Science, 29, 90–98.
• Boerma, H. R., & Specht, J. E. (2004). In: Boerma, H. R., & Specht, J. E. (eds.). Soybeans: Improvement, Production, and Uses. ASA–CSSA–SSSA.