Potential Transpiration

Crop transpiration occurs as the plant emerges and continues until the crop reaches maturity (see Crop development), transpiration being zero outside this period of crop growth.

Daily rates of potential transpiration (TPd, kg m-2 d-1) serve as a guide line for determining TAd and crop growth. TPd is a function of the evapotranspiration model. Daily potential crop evapotranspiration (ETPd, kg m-2 d-1), assuming a disease and pest-free, well-fertilized crop, grown in large fields under optimum soil water conditions is estimated as:

where ET0d (kg m-2 d-1) is the daily reference crop evapotranspiration (ET component, http://www.sipeaa.it/tools), k'c (unitless) is a crop coefficient equal to:

where kc (unitless, ranging from 0.8 to 1.4; reference values for selected crops in the table below) is the crop coefficient at full canopy, GLAI (m2 m-2) is the green leaf area index, CGD (°C-d) is the accumulated thermal time since planting, CGDLA (°C-d) is the accumulated thermal time since planting to stop leaf area expansion.

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