Straw return is associated with improved morel cultivation performance and with changes in soil quality and microbial communities.

Returning crop straw to soil is a cornerstone practice for sustaining soil quality in grain cropping systems, yet its application to edible fungal cultivation has received comparatively little attention. Here we report a field study of rice straw incorporation in morel (Morchella sextelata) production, conducted across two cultivation sites, Xindu and Santai, in Sichuan, China. Five treatments differing in straw physical form were compared. The results showed that morel performance differed with straw physical form rather than with the presence of straw alone. Fruiting bodies formed only at the carbon-rich, nearly neutral Xindu site, where straw applied as 3-5 cm segments (T1) was associated with the largest increases in fresh yield (+ 72.2%) and in the proportion of commercial-grade fruiting bodies (+ 46.7%), together with a 23.3% higher soil quality index relative to the unamended control. At the alkaline, carbon-poor Santai site, mycelial colonization was extensive under T1, with M. sextelata reaching 29.3% of fungal reads, yet no ascocarps developed. Measured contrasts included lower soil organic carbon, higher pH and fewer days with surface temperature below 5 °C at Santai than at Xindu. T1 also showed the lowest microbial nutrient-limitation intensity at both sites. Morel yield correlated positively with urease activity, a proxy for microbial N-acquisition investment, and negatively with soil organic carbon and the soil carbon-to-nitrogen ratio (all P < 0.05). Mantel tests further revealed that, at Xindu site, NH