• Step 1: Calculate Total Nitrogen Applied:

$$\text{Urea Applied} = 220\text{ kg/ha}$$ $$\text{N content of Urea} = 46\%$$ $$\text{Nitrogen Applied (N)} = 220 \times 0.46 = 101.2\text{ kg N/ha}$$

• Step 2: Calculate Yield Increase over Control:

$$\text{Yield in Fertilized Plot } (Y_f) = 6\text{ t/ha} = 6,000\text{ kg/ha}$$ $$\text{Yield in Control Plot } (Y_0) = 3\text{ t/ha} = 3,000\text{ kg/ha}$$ $$\Delta Y = 6,000 - 3,000 = 3,000\text{ kg/ha}$$

• Step 3: Calculate Agronomic Efficiency ($AE_N$):

$$AE_N = \frac{Y_f - Y_0}{\text{N applied}} = \frac{3,000\text{ kg grain}}{101.2\text{ kg N}} \approx 29.64\text{ kg grain / kg N applied}$$

• Conclusion: Agronomic efficiency is 29.6 kg grain / kg N applied. (Correct answer: Option 4)