Page 358 - FRUTAS DEL TRÓPICO

358 Frutas del trópico

Where ΔS is the change in soil water storage, R is rainfall, I is irrigation, ET is evapotrans-
piration, and D + RO is drainage and runoff. Once the soil water desired is obtained in a field

ΔS becomes 0, and Eq. 1 is reduced to:

I= ET - R + (D + RO) (2)

Next, the remaining variables (ET, D, and RO) are estimated.

ET: evaporation and transpiration

Evaporation from the soil surface is a key component in the water balance and makes

up a portion of the ‘ET’ variable. Hence, estimation of evaporation is important for designing
irrigation systems. Evaporation can be measured using soil moisture probes or volumetric soil

sampling methods.

The remaining portion of the ‘ET’ variable is transpiration. Transpiration is the loss of wa-

ter from leaves, mostly through stomata, but a little is lost through the cuticle. Transpiration can

be measured using technology such as a sap flow system (e.g., http://www.dynamax.com/).

Figure 1: Water balance for a field crop (http://www2.dpi.qld.gov.au/images/7452)jpg)

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