Abstract Water shortage is becoming a severe problem in
arid and semi-arid regions worldwide, reducing the availability
of agricultural land and water resources. Deficit
irrigation strategies can improve water-use efficiency and
the sustainability of agro-ecosystems, although it is important
to model the effects on yield loss due to irrigation
water restrictions. This work estimates the water production
function in citrus trees, determining the relationship
between plant water stress and yield depression, as well
as establishing a mathematical model for each phenological
stage considered (flowering, fruit growth and ripening), and
for the entire productive process. For three consecutive
years (2006–2008), four regulated deficit irrigation treatments
plus a control (100% crop water evapotranspiration
(ETC)) were implemented in 13-year-old citrus trees (Citrus
sinensis L. Osb. cv. Navelina). Different water production
functions were determined for each phenological stage,
establishing the relationship between the irrigation water
stress and crop yield. Our results show that the fruit growth
and flowering stages were the most sensitive periods in
relation to irrigation water deficit and yield loss. Water
stress close to 50% of ETC during the flowering stage
would impose a yield loss of up to 20%, whereas this same
water stress level during the fruit growth or ripening stages
would result in yield losses of nearly 10% and 6%,
respectively. The adjustment with cross terms (r
2
=0.87)
estimated the yield loss with good accuracy, being very
similar to data measured in each study season. Consequently,
the combined effect of deficit irrigation in differen