Glycinemax

Soy (Glycinemax) is one of the most important agricultural crops globally, both for its economic value and its unique biology. In Brazil, the world's largest exporter, soybeans occupy around 50% of the area cultivated with grains.

The taxonomic classification of Glycine max:

• Domain: Eukarya

• Kingdom: Plantae

• Phylum: Tracheophyta

• Class: Magnoliopsida

• Order: Fabales

• Family: Fabaceae (Leguminosae)

• Genre: Glycine

• Species: Glycinemax

Its adaptability to different climates and soils, combined with its ability to fix atmospheric nitrogen, reduces dependence on synthetic fertilizers, promoting more sustainable agricultural systems.

Originating in China, where it was domesticated millennia ago from its wild ancestor (Glycine soja), soybeans have evolved into an essential commodity, providing vegetable protein, edible oil and raw material for biodiesel.

Morphology and anatomy

Soybean is a dicotyledonous plant with morphological characteristics that support its productivity and adaptation.

Raiz: the root system is pivotal, with a main root and lateral roots that house symbiotic nodules with bacteria of the genus Bradyrhizobium. These nodules perform biological nitrogen fixation (BNF), essential for soil fertility and reducing nitrogen fertilization costs.

Stem: cylindrical and pubescent, the stem varies from 0,5–2 m in height, depending on the cultivar and environmental conditions. The pubescence protects against pests and reduces water loss.

Sheets: They are trifoliate, with three leaflets with reticulate venation, arranged alternately in opposite pairs. The greater concentration of stomata on the underside and the leaf pubescence minimize transpiration and protect against herbivores.

Flowers: Small and yellowish, the flowers are hermaphrodite and predominantly autogamous. The floral structure favors self-pollination, although cleistogamy (fertilization before the flower opens) can occur under specific conditions.

Fruits and seeds: The fruits are simple pods containing 2–4 seeds. The seeds, rich in protein (35–45%) and oil (18–22%), have variable coloration (yellow, green, white or black), depending on genetics and maturity.

Physiology and metabolism

Soybeans perform C3 photosynthesis, which is efficient under conditions of high humidity and moderate temperatures, but less productive under intense heat or water stress. The photosynthetic rate depends on light availability, CO₂ concentration and soil moisture.

The plant has a high transpiration rate and is sensitive to water deficiency, especially during the grain filling phase (R5). Supplemental irrigation is recommended in regions with water deficit during this stage.

FBN is a key process, mediated by Bradyrhizobium japonicum e Bradyrhizobium elkanii, which convert atmospheric nitrogen (N₂) into ammonia (NH₃). To maximize BNF, inoculation with selected strains (e.g. SEMIA 5079 and 5080) and maintenance of soil pH between 5,5 and 6,5 are recommended.

Soybeans require adequate levels of macronutrients (N, P, K) and micronutrients (e.g. Zn, B). Soil analyses are essential to define fertilizer doses, especially phosphorus (30–60 kg/ha of P₂O₅) and potassium (40–80 kg/ha of K₂O), adjusted to the expected productivity.

Life cycle and reproduction

The soybean cycle is divided into vegetative (V) and reproductive (R) phases, according to the BBCH scale.

Vegetative phase (V1–Vn): begins with seedling emergence and ends with flowering. Includes the development of true leaves, stem elongation and formation of root nodules, with effective nodulation from V2–V3, depending on inoculation and soil conditions.

Reproductive phase (R1–R8): begins with flowering (R1) and ends with physiological maturity (R7) and harvest (R8). The R5 phase (grain filling) is critical, being sensitive to water stress, pests and diseases.

Phytosanitary challenges in Brazil

In Brazil, pests, diseases and weeds can reduce soybean productivity if not adequately controlled.

Some examples of crop phytosanitary problems:

• Bittergrass (Digitaria insularis) and horseweed (conyza bonariensis): resistant to glyphosate. Use herbicides with alternative modes of action.

• Asian rust (caused by Phakopsora pachyrhizi): Biotrophic fungus that causes necrotic spots and defoliation. Can reduce productivity by up to 80% without control (Embrapa, 2023). Use fungicides and resistant cultivars.

• Soybean caterpillar (Anticarsia gemmatalis): larvae defoliate plants, especially in the reproductive phase. Monitoring with pheromone traps is recommended.

• Target spot (caused by Corynespora cassiicola): affects leaves and pods in humid climates. Monitoring and preventive fungicides are essential.

• White mold (caused by Sclerotinia sclerotiorum): causes rot in humid areas. Crop rotation and adequate spacing reduce incidence.

• Nematodes (Meloidogyne incognita, Heterodera glycines): attack roots, compromising nutrient absorption. Rotation with non-host crops is effective.

• Bedbugs (Euschistus heros, Nezara viridula): pierce pods and grains, reducing weight and quality. Control with insecticides in the R3–R5 phase.

• Trapoeraba (Commelina benghalensis): control with post-emergent herbicides and mechanical management.

Integrated management recommendations

Monitoring: Weekly inspection for Asian rust and pests. Use of traps for bedbugs and caterpillars.

Chemical control: Fungicide rotation to avoid resistance (e.g. triazoles + strobilurins). Herbicides with different modes of action for resistant weeds.

Cultural practices: planting at recommended times. Density of 300.000–400.000 plants/ha. Crop rotation to reduce nematodes and white mold.