Water footprint and production of rain-fed saffron under different planting methods with ridge plastic mulch and pre-flowering irrigation in a semi-arid region

Most of the saffron cultivation areas in Iran are irrigated and with pre-flowering irrigation being necessary to facilitate flower emergence. However, the growers face shortage of water. Post- flowering rain-fed (PFRF) saffron cultivation could be a solution, and ridge and furrow rainfall harvesting (RFRH) with plastic mulch could be used to collect runoff in the field planting areas. In this regard, the objectives of this study were to determine the effects of interaction of two different saffron planting methods (basin and furrow planting), using plastic mulch and without plastic mulch on ridge of the furrow planting, using irrigation at pre-flowering and without irrigation on saffron growth, yield, yield components, economic water productivity (EWP) and water footprint of saffron in two growing seasons with low (167 mm) and high (367 mm) seasonal rainfall in a semi-arid region. Without irrigation in pre-flowering (NPFI) produced a saffron yield reduction of 70% compared with pre-flowering irrigation (PFI). It is concluded that 90 mm of irrigation water should be applied as PFI for adequate flowering and yield. In addition, the use of the RFRH system resulted in a runoff coefficient of 0.85 and increased soil water storage (48% at low seasonal rainfall), saffron yield (51%), leaf dry matter, LDM (90%) and EWP (17%). The blue water footprint (BWF) with low rainfall (165 mm) was higher than that with abundant rainfall (367 mm), because saffron yield in the second year was lower due to the older age of saffron in field, which resulted in lower yield and consequently higher BWF. Likewise, green water footprint (GWF) was higher (4810 m3 kg−1) than those that obtained as BWF (739 m3 kg−1) due to the fact that pre-flowering irrigation is necessary for onset of flower and the regional rainfall is insufficient to initiate flowering. The effects of low seasonal precipitation (less than 200 mm) on saffron were manifested in yield and LDM reduction of 70% and 42%, respectively, compared to high seasonal precipitation, decreasing as seasonal precipitation increased. Precipitation reached around 300 mm in rain-fed with pre-flowering irrigation caused no reduction in saffron yield and LDM. Therefore, in PFRF conditions, furrow planting with ridge plastic mulch and pre-flowering irrigation is recommended. The economic water footprint of saffron under PFRF conditions with PFI was 50% of that obtained for irrigated saffron production, which is preferable in virtual water trade.