Performance of soy-winter wheat relay intercropping under various water conditions

Relay intercropping can increase yields, grow two crops per year in regions where only one is possible, and provide ecological benefits. Nevertheless, relay intercropping is uncommon in Europe and its suitability as a crop diversification strategy is unknown. Using a three-year field trial in eastern Germany, this study sought to understand under which management the system is most viable and how competition for light and water affects yields. We studied soy-winter wheat relay intercropping in a plot trial with three cropping systems (sole wheat, sole soy, and relay intercropping), two winter wheat varieties, and two irrigation treatments (irrigated and rainfed). We measured yield, crop biomass, soil moisture, and intercepted photosynthetically active radiation throughout the growing season. We found that in two of the three experimental years, relay intercropped soy had low or no yield and that the land equivalent ratio (LER) of the system barely reached 1 under any treatment. Water stress negatively affected intercropping as winter wheat outcompeted the soy and the growth-stunted soy received only 40–80 % of the PAR sole soy received. Even after the wheat harvest, intercropped soy did not fully recover and reached 80 % of the sole soy biomass in the best case, but in some years 0–40 %. Using vigorous winter wheat and narrow-row management for productivity appears to cause water stress in soy. Future research should focus on mitigating water competition and identifying arrangements and varieties adapted to competition. • Intercropped soy yields were generally very low and the LER of intercropped systems rarely reached 1. • Irrigation increased intercropped soy yields indicating water competition in the system. • Low soil moisture at soy sowing led to total failure of the intercropped soy crop in 2022. • Strong water deficits during the soy-wheat co-growth phase impaired intercropped soy growth. • Intercropped soy also suffered from competition for light as it received only 45–80 % of the PAR measured at the sole soy canopy.