Principles of Agronomy & Cropping Systems

Principles of soil tilth and aggregate dynamics:

• Statement (I) is correct: Tilth is the physical condition of soil in relation to plant growth, defined by two fundamental aspects: size distribution of soil aggregates and the mellowness or friability of the seedbed.
• Statement (II) is correct: In irrigated agriculture, a higher proportion of larger aggregates ($\gt 5\text{ mm}$) is necessary to prevent surface crusting, slaking, and excessive soil dispersion under frequent watering, whereas dryland agriculture requires smaller aggregates ($1-2\text{ mm}$) to retain moisture.

USDA particle size classification scheme:

• Very coarse sand: $2.0-1.0\text{ mm}$
• Coarse sand: $1.0-0.5\text{ mm}$
• Medium sand: $0.5-0.25\text{ mm}$
• Fine sand: $0.25-0.10\text{ mm}$ (upper diameter limit is $0.25\text{ mm}$)
• Very fine sand: $0.10-0.05\text{ mm}$
  (F) Silt: $0.05-0.002\text{ mm}$; Clay: $\lt 0.002\text{ mm}$. Hence, $0.25\text{ mm}$ corresponds to the fine sand fraction class threshold.

• In Square planting geometry, the inter-row spacing equals the intra-row plant-to-plant spacing ($R \times P$, e.g. $20\text{ cm} \times 20\text{ cm}$ or $1\text{ m} \times 1\text{ m}$).
• This equidistant spatial arrangement provides each individual plant with an identical radial ground area and symmetrical foliage distribution.
• Consequently, mutual shading is minimized and uniform interception and incidence of solar radiation is achieved from all compass directions throughout the daylight hours.
• Hence, Square planting (Option 1) is the correct answer.