Rice–Loach Co-Culture: Increased Rice Grain Yield and Positive Effects on Root Morphological and Physiological Traits

Root morphological and physiological traits play important roles in rice growth and yield formation. Rice–loach co-culture is an important integrated rice–aquaculture system, yet root responses under ditch-free co-culture conditions remain poorly understood. In this study, conventional and hybrid rice cultivars were grown under monoculture and rice–loach co-culture to evaluate the effects of rice type and cropping pattern on root traits and grain yield. Our results indicated that the interaction between rice type and cropping pattern significantly affected several root traits and 1000-grain weight but had no significant effect on final grain yield. Compared with monoculture, rice–loach co-culture significantly reduced bulk density by 10.5–14.6% and increased total porosity by 12.7–12.9%. Rice–loach co-culture also significantly enhanced early root physiological activity, increasing root oxidative activity by 5.70–6.50% and root bleeding intensity by 12.6–13.9% at tillering. Meanwhile, root biomass at maturity significantly increased by 20.0–34.4%, and grain yield significantly increased by 14.3–19.7%. Rice type also significantly affected root traits: hybrid rice generally exhibited more favorable root morphological traits, greater physiological activity and biomass, and higher grain yield than conventional rice. Overall, the rice–loach co-culture system exhibited improved soil physical properties, greater root physiological activity and growth, and higher grain yield than rice monoculture, while hybrid rice performed better than conventional rice within this system.