Background and aims <p>Saffron (<i>Crocus sativus</i> L.) is one of the most precious plant in the world. This study aimed to evaluate the effect of cow manure and zeolite on radiation use efficiency (RUE) of saffron under deficit irrigation (DI).</p> Methods <p>A two-year split-split plot experiment was conducted in a semi-arid region of Iran (2020–2022) with three DI levels (100%, 75%, and 50% of water requirement), cow manure (15, 30, and 45 t ha⁻¹), and zeolite (0, 5, and 10 t ha⁻¹). Key parameters measured included leaf area index (LAI), light extinction coefficient (<i>k</i>), fraction of intercepted photosynthetically active radiation (IPAR), and RUE.</p> Results <p>The results showed that the fraction of IPAR depended on LAI and <i>k,</i> which affected accumulation IPAR and consequently leaf dry matter for saffron. <i>k</i> and RUE ranged from 0.47 to 0.85 and 0.62 to 1.55&#xa0;g&#xa0;MJ⁻¹ in the first growing season and 0.75 to 1.31 and 0.64 to 1.40&#xa0;g&#xa0;MJ⁻¹ in the second growing season, respectively. In most treatments, <i>k</i> increased and RUE decreased due to DI in two growing seasons. However, the manure and zeolite mitigated this reduction. Despite having the lower LAI, leaf dry matter and fraction of IPAR, the first growing season had lower <i>k</i> values than the second growing season. Field age also impacted RUE differently across treatments.</p> Conclusion <p>Manure and zeolite reduced the negative impact of DI on saffron by improving <i>k</i> and RUE, making them suitable for sustainable cultivation and improving saffron growth models under stress conditions.</p>