Optimizing wheat-maize relay intercropping in semi-arid regions of Iran to mitigate late sowing challenges and enhance water productivity in grain maize

In semi-arid regions with short growing seasons, grain maize as a second crop after autumn cereals is often limited, leading to reliance on silage. This two-year (2021–2023) field study in Karaj, Iran, evaluated wheat–maize relay intercropping to extend the maize growing period and improve water productivity. Three scenarios were compared: (1) relay intercropping of maize into standing wheat before the final wheat irrigations; (2) no-till maize planted into wheat residues after wheat harvest; and (3) conventional sequential wheat and maize cultivation. Relay intercropping increased maize yield by 36% and 35% over no-till in years 1 and 2, respectively, but reduced wheat yield by up to 58%. Irrigation water use was reduced by approximately 1,200 m³ ha−1 in relay intercropping, with water productivity improving from 0.88 to 1.50 kg m−3 in year 1 and 0.70 to 1.17 kg m−1 in year 2. The land equivalent ratio was 2.03 in year 1 and 1.77 in year 2, indicating higher productivity than sole cropping. In contrast, maize in the conventional system failed to mature due to a shortened season. Relay intercropping proved to be a productive and water-efficient approach for grain maize cultivation under short-season, water-limited conditions.