Long-term optimization of saffron yield and economic water productivity as influenced by irrigation water depths, salinity levels, and planting techniques.

Saffron (Crocus sativus L.) is one of the most valuable spice crops in the world, but its productivity is highly sensitive to water availability, soil salinity, and cultivation methods. In many arid and semi-arid regions, where saffron is typically grown, water scarcity and soil salinization are growing challenges that threaten both yield and profitability. Long-term effect of irrigation water salinity in 4 levels [S1 = 0.42 dS m− 1 (freshwater) to 3.0 dS m− 1], depth of irrigation water in 3 levels (100–50% of water requirement, WR), and two planting methods (P1: basin and P2: in-furrow) on saffron growth, yield and water productivity were studied. In the basin planting, maximum saffron yield (SY) obtained only in the fourth growing season as 12.0 kg ha− 1 with 868 mm of rain plus irrigation water. However, in the in-furrow planting, maximum SY occurred during the second to fourth growing seasons as 13.0 kg ha− 1 in each year with 832 mm of rain plus irrigation water. Decreasing trend of saffron growth in all the treatments intensified from the fifth growing season onwards. In general, the mean of saffron yield over all growing seasons varied as 8.65–7.43 kg ha− 1 with increasing salinity from 0.42 to 3.0 dS m− 1. This was 8.5–7.31 kg ha− 1 for irrigation water varied from 100% WR to 50% WR. Results also showed that the total SY in six growing seasons in the in-furrow planting was 1.59 times that in the basin planting. The leaf dry matter (LDM), corm yield (CY), and harvest index (HI) decreased in the sixth growing season compared to that in the fifth growing season by 38.4%, 62.0%, and 82%, respectively. It is concluded that saffron is a plant highly sensitive to salinity, and water salinity of 2.0 and 3.0 dS m− 1 resulted in 22% reduction in total saffron yield. Mean soil salinity was doubled from 0.7 to 1.3 dS m− 1 at the last years that saffron cultivation should be terminated. The benefit-cost ratio (BCR) in the third to fifth growing season under different treatments was higher than 1.0 (as 1.87, 2.42, and 2.23, respectively) indicating economic feasibility of saffron crop production. However, in the sixth growing season, BCR was 0.23 that was not feasible. Therefore, according to the results of SY, CY and BCR, the farmer should terminate the saffron cultivation, and harvest the corm at the end of the fourth and fifth growing season in the in-furrow planting and the basin planting, respectively. The average economic irrigation water productivity (EWPi) in the fourth growing season was 2.2 times its value in the third growing season. However, in the fifth, compared to the fourth growing season, it decreased by 38%.