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Introduction

• Plasticity of Soy: High adaptability of soy varieties (Glycine max) to different environmental and management conditions, evidenced through morphological changes.

• Objective of Study: Evaluate the effects of varying densities of soybean cultivar BRS 8381 on agronomic characteristics.

Experimental Design

• Location: Experiment conducted in the Cerrado area, Agua Boa of Embrapa Roraima.

• Design: Randomized block design in a 2x4 factorial scheme with four replications.

• Treatments:

  • Years of cultivation: 2015 and 2016

  • Plant densities: 10, 14, 18, and 22 plants per linear meter

• Measured Attributes:

  • Plant height (PH)

  • Height of insertion of the first pod (HIFP)

  • Stem diameter (SD)

  • Number of nodes on the stem (NNS)

  • Number of pods per plant (NPP)

  • Number of branches per plant (NBP)

  • Dry mass of plant (DMP)

  • Harvest index (HI)

  • Grain yield (GY)

Agronomic Characteristics

Findings

• Max Productivity: Highest average productivity for BRS 8381 is achieved with a population of 387,448 plants per hectare.

• Unsuitable Density: 22 plants per meter is not suitable for Roraima's Cerrado conditions.

• Influencing Factors: Rainfall and temperature significantly affect BRS 8381's growth patterns.

Material and Methods

• Climate: Rainy tropical climate with

  • Annual rainfall: 1667 mm

  • Avg. temperature: 27.4°C

• Soil Type: Dystrophic Yellow Latosol (LAdx) with specific nutrient concentrations.

• Experimental Setup:

  • Each plot consisted of 8 linear meters, maintaining density treatments.

  • Cultural treatments included pest, disease, and weed control based on established recommendations.

Measurements of Agronomic Characteristics

• Plant Height Measurement: Height measured from ground to plant apex.

• Stem Diameter Measurement: Measured at the insertion of the first pod using a digital caliper.

• Dry Mass Determination: Conducted by weighing dried plant material after 72 hours in an oven.

• Yield Measurements: Grain yield calculated post-harvest based on kg per hectare.

Results and Discussion

Vegetative Characteristics

• Height & Nodes:

  • Linear growth response in height based on density, significant increase in 2016.

  • Node count varies with density across years; 2016 showed no variation.

• Contributory Factors:

  • Interrelation between growth habit changes due to rainfall and light conditions.

Characteristics That Influence Productivity

• Stem Diameter: Variant by year and density, important for lodging resistance.

• Branch Count: Decreased with increased density, linked to light availability.

• Plant Dry Mass: Correlated with lower densities showing higher biomass.

Productive Characteristics

• Pods and Grain Mass:

  • Number of pods per plant and dry grain mass influenced by density and cultivation year.

  • Dry grain mass increases observed in 2016 compared to 2015, correlating to plant density.

• Harvest Index: No significant treatment effect identified; influenced by environmental conditions.

Conclusion

• Optimal Density: BRS 8381 achieves highest average productivity at about 19.37 plants per linear meter.

• Environmental Impact: Conditions in Roraima significantly affect the growth and yield of soybean.

• Recommendations: Adjust planting density accordingly to maximize productivity, particularly avoiding high-density planting which may hinder grain yield.