In the FAO-56 single crop coefficient approach ($ET_c = K_c \cdot ET_0$), during which developmental stage does the crop coefficient $K_c$ reach its maximum plateau value for typical field crops?
Options:
(A) Mid-season stage (full effective ground cover and flowering/grain formation)
(B) Initial stage (germination and early seedling emergence)
(C) Late-season stage (crop senescence, leaf yellowing, and harvest maturity)
(D) During pre-sowing fallow period
Answer Key:
A
Step-by-Step Solution & Explanation
The crop coefficient curve ($K_c$) exhibits four distinct stages:
1. Initial stage: Soil evaporation dominates ($K_c \approx 0.3 - 0.5$).
2. Crop development: Rapid canopy expansion.
3. Mid-season stage: Full vegetative cover, maximum transpiration, LAI $\ge 3$, where $K_c$ peaks ($1.05 - 1.25$).
4. Late season: Senescence and maturity where stomatal closure and leaf drop decrease $K_c$. Option A is correct.