Under the background of the worsening global food and water crisis, efficient agricultural practices have become increasingly important. This study investigated the impact of different irrigation and cultivation modes on rice growth parameters, gas exchange, rice yield components, and water footprints in Jiangsu, China. Four treatments were employed in a randomized complete block design with three replications: (i) transplanted rice with frequent shallow irrigation (T-FSI), (ii) transplanted rice with rain-catching and controlled irrigation (T-RCCI), (iii) direct-seeded rice with frequent shallow irrigation (D-FSI), (iv) and direct-seeded rice with rain-catching and controlled irrigation (D-RCCI). The results revealed that the D-RCCI treatment significantly improved growth and physiological parameters. The D-FSI treatment drastically increased rice yield whereas T-RCCI increased the stem bending resistance and reduced lodging risk. The water footprint analysis showed significant water savings by optimized management practices. Compared to T-FSI, the T-RCCI, D-FSI, and D-RCCI treatments reduced the blue-green water footprint by 33%, 25%, and 25%, respectively. Additionally, water production efficiency increased by 13%, 106%, and 154% for T-RCCI, D-FSI, and D-RCCI respectively. The water footprint per unit yield of T-RCCI, D-FSI, and D-RCCI treatments was significantly reduced by 12%, 5,3%, and 63% compared to T-FSI. Overall, D-RCCI is the optimal strategy for rice cultivation in Jiangsu province and similar climatic areas due to its positive impact on yield, water savings, and environmental benefits.

To identify an optimized management strategy for the safe reuse of aquaculture wastewater in saline–alkali paddy fields, a pot experiment was conducted to investigate the interactive effects of irrigation modes (flooded and shallow–wet) and Chlorella application on wastewater purification, nitrogen and phosphorus transport, and rice yield. The results showed that Chlorella effectively improved the removal rates of nitrogen and phosphorus in field surface water, but its efficacy depended on the irrigation mode. The purification efficiency of shallow–wet combined with Chlorella (I_SC_W) was highest, and the removal rate of total phosphorus at the heading stage was 88.67%. The leaching risk of deep nitrate nitrogen (NO₃⁻-N) was the lowest, but the rice yield was significantly reduced. In contrast, flooded irrigation combined with Chlorella (I_FC_W) produced the highest rice yield, whereas its water purification effect was moderate. The entropy-weighted TOPSIS evaluation further indicated a clear trade-off. I_SC_W improved phosphorus removal in surface water, but reduced grain yield by 60.7% compared with I_FC_W. These findings demonstrate that irrigation mode is a key factor in regulating the purification effect of Chlorella and its trade-off with rice yield. These findings provide theoretical support for wastewater resource utilization in saline–alkali regions and contribute to the sustainable development of coastal agriculture.