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Implementing water-saving irrigation techniques and drought-tolerant crops is essential for sustainable agriculture under drought and water scarcity. This study evaluated the effects of three irrigation strategies of full irrigation (FI), partial root-zone drying (PRD) at 70 % FI, and conventional deficit irrigation (DI) at 70 % FI, three lateral spacings (20 cm, 40 cm, 60 cm), and two drip irrigation systems (surface drip (SD) and subsurface drip (SSD)) on water use, crop water productivity, yield, and root growth of spring safflower (cv. Goldasht) in a semi-arid region in Iran over two growing seasons. The split–split plot experiment revealed that FI with 20 cm spacing achieved the highest seed yield. PRD and DI saved 25 % of irrigation water, with mean seed yield reductions of 9.4 % and 13.6 %, respectively, compared to FI. Increasing lateral spacing to 40 cm and 60 cm reduced yield by 4.5 % and 24.3 %. Root growth was positively correlated with seed yield; higher root length density (RLD) and root mass density (RMD) were observed where soil water content was greater. Water-saving treatments enhanced specific root length (SRL). SSD improved crop water productivity compared to SD. Maximum WP CET , WP irrig , and WP irrig+rain were achieved with PRD under SSD at 20 cm and 40 cm spacings, while the lowest values were found under FI with SD at 60 cm spacing. Yield response factor (K y ) and yield sensitivity index (λ i ) analyses indicated that 20 cm lateral spacing enhanced drought tolerance. We conclude that SSD with 40 cm spacing under PRD at 70 % FI is an effective alternative for water-scarce regions, balancing water savings with minimal yield loss. • Partial root zone drying (PRD) and deficit irrigation (DI) saved 25 % of applied water. • Subsurface drip irrigation (SSD) with 20 lateral spacing maximized crop water productivity in PRD. • SSD with 40 cm lateral spacing under PRD had 9 % yield penalty compared to FI. • Soil layers with higher water content had higher root length and root mass densities. • PRD and DI produced higher specific root length.
Karizi et al. (Mon,) studied this question.