Unit 4

• FAO-56 Penman-Monteith Reference Surface:
• The standard reference crop ($ET_0$) is mathematically defined as a hypothetical cool-season green grass reference crop with specific bio-physical characteristics:
• Assumed uniform crop height of 0.12 m (12 cm)
• Fixed surface resistance of $70\text{ s/m}$
• Albedo of $0.23$. (Correct answer: Option 1)

• Type I Error ($\alpha$): Occurs when a true null hypothesis ($H_0$) is incorrectly rejected.
• Level of Significance: The probability of committing a Type I error is denoted by $\alpha$ and represents the level of significance of the statistical test ($\alpha = P(\text{Reject } H_0 \mid H_0 \text{ is true})$), typically set at 0.05 or 0.01.

Correct option: (4) Level of significance

• Experimental Error: The variation among experimental units treated alike, arising from uncontrolled extraneous factors, spatial soil heterogeneity, genetic variability among units, and measurement noise.
• Role in ANOVA: Provides the baseline variance against which treatment variance is tested in the F-test ($F = \text{MS}_{\text{Treatment}} / \text{MS}_{\text{Error}}$).

Correct option: (3) Experimental error