where Re is the effective fraction (0.1-1.0) of water applied, that is, after estimating the losses by evaporation and wind drift; and Oe is the effective fraction (0.9-1.0) of water discharged, that is, after estimating the losses from leakage.
Re expresses how the application efficiency is affected by evaporation and wind drift as influenced by the size of the droplets. Re can be computed from the foreseen values of reference évapotranspiration ET0 (mm day 1), wind speed WS (km h 1), and the coarseness index CI:
- CI(0.00043 ET0 - 0.0018 WS + 0.000016 ET0WS) (5.152)
for CI such that, if CI < 7, let CI = 7; if CI > 17, let CI = 17.
CI is an empirical estimate for the size of droplets produced by the sprinkler as a function of the operating pressure P (kPa) and of the nozzle diameter dn (mm):
The gross application depth D then is calculated from the net irrigation depth In (see Section 5.1.6) and the efficiency Epa. When irrigating with saline water or in saline soils, a leaching fraction LFmust be added (see Section 5.6):
where D is the gross application depth (mm), In is the net irrigation depth (mm), and Epa is the design application efficiency (%).
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