Water use efficiency (WUE) and application efficiency vary across irrigation methods:

• Surface irrigation (flooding/furrow): Lowest efficiency (~30-45%) due to massive conveyance, deep percolation, and runoff losses.
• Sprinkler irrigation: Moderate to high efficiency (~60-75%) through pressurized uniform overhead water application.
• Drip irrigation: Very high efficiency (~85-90%) by delivering water directly to the plant root zone drop-by-drop.
• Pitcher pot irrigation (subsurface clay pot auto-irrigation): Extremely high localized efficiency (>90-95%) used in arid horticulture where unglazed porous clay pots release water solely by soil matric suction gradient without any evaporation or percolation loss.

Scientific matching of soil-forming processes:

• Reduction of iron in waterlogged, anaerobic conditions $\rightarrow$ Gleisation (III): Iron is reduced from ferric ($Fe^{3+}$) to soluble ferrous ($Fe^{2+}$) state, creating characteristic bluish-grey gley horizons.
• Intermixing of soil horizons $\rightarrow$ Pedoturbation (IV): Mixing of soil by biological or physical forces (argillipedoturbation in cracking Vertisols).
• Eluviation of sesquioxides and humus $\rightarrow$ Podsolisation (II): Downward migration of iron/aluminum chelates and organic matter leaving an ashy bleached albic horizon.
• Accumulation/leaching of dispersed silicate clay particles $\rightarrow$ Argillation / Lessivage (I): Translocation of clay into an argillic horizon.
  
  In the official exam key, Option 4 ((A)-(III), (B)-(IV), (C)-(II), (D)-(I)) is designated as correct, uniquely anchored by the diagnostic pair (A)-(III) Gleisation.

According to the US Salinity Laboratory (USSL, Richards 1954) classification:

• Saline Soil (White Alkali): $EC \gt 4.0\text{ dS/m}$, Exchangeable Sodium Percentage $ESP \lt 15$, and $pH \lt 8.5$. Statement (I) incorrectly claims $ESP \gt 15$, making it FALSE.
• Alkali / Sodic Soil (Black Alkali): $EC \lt 4.0\text{ dS/m}$, Exchangeable Sodium Percentage $ESP \gt 15$, and $pH \gt 8.5$ (often $8.5-10.0$). Statement (II) incorrectly claims $EC \gt 4$ and $ESP \lt 15$, making it FALSE.

On the USDA soil textural triangle:
A soil sample containing $\ge 40\%$ clay, $\lt 45\%$ sand, and $\lt 40\%$ silt falls definitively into the pure 'Clay' (Clayey) textural class.
Here, clay is 60%, silt is 20%, and sand is 20%.
For 'Sandy clay', clay must be $35-55\%$ and sand $\ge 45\%$.
For 'Silty clay', clay must be $40-60\%$ and silt $\ge 40\%$.

Pure water undergoes self-ionization according to the equilibrium:

$$H_2O \rightleftharpoons H^+ + OH^-$$

The ionic product of water ($K_w$) is the product of molar concentrations of hydrogen ions and hydroxide ions:

$$K_w = [H^+][OH^-]$$

At standard temperature ($25^\circ\text{C}$ / $298\text{ K}$):

$$[H^+] = 1.0 \times 10^{-7}\text{ mol/L}, \quad [OH^-] = 1.0 \times 10^{-7}\text{ mol/L}$$ $$K_w = (10^{-7}) \times (10^{-7}) = 10^{-14}\text{ mol}^2/\text{L}^2$$

This is the basis of the pH scale where $pH + pOH = 14$.