• Formula for Field Water-Use Efficiency (WUE):

$$\text{Field WUE} = \frac{\text{Crop Yield (kg/ha)}}{\text{Total Water Used (ha-mm)}}$$

• Given Values:
• Grain Yield = $4.5\text{ t/ha} = 4.5 \times 1000 = 4,500\text{ kg/ha}$
• Water Requirement = $45\text{ cm} = 45 \times 10 = 450\text{ mm}$
• Calculation:

$$\text{Field WUE} = \frac{4,500\text{ kg/ha}}{450\text{ mm}} = 10\text{ kg/ha-mm}$$

• Conclusion: The field water-use efficiency of the wheat crop is 10 kg/ha-mm. (Correct answer: Option 2)

• Latin Square Design (LSD): A single-factor experimental design where a single set of treatments is arranged in a square grid to eliminate two perpendicular sources of extraneous soil heterogeneity (row blocking and column blocking simultaneously). (Correct answer: Option 3)
• Factorial RCBD: Multi-factor design studying two or more factors and their interaction effects.
• Split-plot Design: Multi-factor design where main-plot factors require large operational plots and sub-plot factors require smaller precision plots.
• Strip-plot (Split-block) Design: Two-factor design where both factors require large contiguous strips perpendicular to each other.

• International Year of Millets (IYM 2023) & UN SDGs: The United Nations declared 2023 as the International Year of Millets to promote climate-resilient nutrition and sustainable agriculture.
• SDGs Directly Supported:
• SDG 2 (Zero Hunger) & SDG 3 (Good Health and Well-being)
• SDG 8 (Decent Work and Economic Growth) through dryland farmer livelihoods
• SDG 12 (Responsible Consumption and Production) through sustainable diversified diets
• SDG 15 (Life on Land) through desertification resistance and soil health
• Distinction: "Nutrition for the most vulnerable" is a specific target/component under SDG 2 rather than an independent designated SDG agenda title in the UN 2030 Agenda framework. (Correct answer: Option 3)

• Urea Hydrolysis Mechanism: Applied urea [$\text{CO(NH}_2)_2$] undergoes enzymatic hydrolysis by the soil enzyme urease to form ammonium carbamate, which rapidly breaks down into ammonium ions ($\text{NH}_4^+$), bicarbonate, and hydroxyl ions ($\text{OH}^-$).
• Normal Neutral Soils: Under favorable moisture and microbial urease activity in neutral soils ($pH\ 6.5–7.5$), urea hydrolysis proceeds rapidly and completes within 2 to 3 days.
• Alkaline / Calcareous Soils: In high pH calcareous/alkaline soils ($pH \gt 8.0$), high initial hydroxyl concentration and osmotic shifts retard optimal urease kinetics and promote intermediate carbonate precipitation, extending complete hydrolysis to about 7 days. (Correct answer: Option 4)