Irrigation strategies for upland rice cultivars in Brazil: Physiological responses and agronomic performance

Irrigation strategies are essential for enhancing water productivity, thereby contributing to the sustainable water management in upland rice (Oryza sativa L.). This study aimed to quantify the effects of various irrigation strategies on the physiology, yield, and irrigation water productivity of three upland rice cultivars. Two shelter experiments (A and B) were conducted using two factors: irrigation managements and cultivars. In Experiment A, three irrigation levels were applied: 100 % (Control), 70 % and 40 % of the irrigation applied in the control. In Experiment B, irrigation was triggered at soil water potential thresholds of −20 and −40 kPa. The cultivars used in both experiments were BRS A501 CL, BRS Esmeralda, and BRS A502. In Experiment A, the Control treatment (100 %) demanded ∼786 mm of water, which yielded 7.9 Mg ha−1, corresponding to an irrigation water productivity of 0.88 kg m−3. Irrigation levels of 70 % (579 mm) and 40 % (371 mm) caused yield reductions of 51–96 % and irrigation water productivity declines of 32–92 %. In Experiment B, the treatment of −20 kPa (683 mm) yielded 6.8 Mg ha−1 and 1.0 kg m−3 of irrigation water productivity. The irrigation threshold of −40 kPa (∼590 mm applied) resulted in an average grain yield of 5.3 Mg ha−1 and irrigation water productivity of 0.89 kg m−3. Overall, although drought-tolerant cultivars were used, water-saving treatments in Experiment A (70 and 40 %) were not suitable for upland rice. In contrast, the −40 kPa irrigation threshold in Experiment B reduced water use while maintaining irrigation water productivity, representing an effective strategy for water-limited environments. Future work should explore irrigation strategies based on Experiment B, targeting specific growth stages.