The correct answer is A. The size distribution of the mineral particles composing the soil.
Soil texture is the relative proportions of sand, silt, and clay in a soil. These three particle sizes are defined by their diameter:
- Sand particles are the largest, with diameters ranging from 0.05 to 2 millimeters.
- Silt particles are intermediate in size, with diameters ranging from 0.002 to 0.05 millimeters.
- Clay particles are the smallest, with diameters less than 0.002 millimeters.
The texture of a soil has a significant impact on its physical properties, such as its ability to hold water and nutrients, its drainage, and its aeration. Soils with a high proportion of sand particles tend to be loose and well-drained, but they also tend to be low in nutrients and organic matter. Soils with a high proportion of clay particles tend to be dense and poorly drained, but they also tend to be high in nutrients and organic matter. Soils with a balanced proportion of sand, silt, and clay particles are considered to be loamy soils, and they tend to have the most favorable physical properties for plant growth.
Option B is incorrect because it refers to the distribution of mineral particles in the soil, not their size. Option C is incorrect because it refers to the crystal distribution in soil, which is not a factor that affects soil texture. Option D is incorrect because it is not a valid option.