Objective To study the value of maize straw and its biochar for substrate improvement in facility cultivation, and explore the response of root architecture of maize to different compound substrates.

Method A pot experiment was carried out, the physicochemical properties of different ratios of substrates and the biomass of aboveground and roots of maize were measured and analyzed. The morphological, fractal and topological structure parameters of maize roots were analyzed and calculated by WinRHIZO (Pro.2020a) root analysis system. SPSS software was used to analyze the correlation of the aboveground/root biomass, root morphological parameters and architectural characteristics.

Result Among the treatments with addition of straw and its biochar, the physicochemical properties of T3 treatment (the addition volumes of vermiculite, perlite, maize straw and maize straw biochar were 22.4, 22.4, 22.4 and 44.8 dm³ respectively) were the most optimized compared to CK, with total porosity and water-holding porosity reaching 81.02% and 55.38% respectively, and the contents of available N, P, and K were all at the optimal level. In T3 treatment, the biomass of the root system, as well as the three main morphological parameters of root length, root surface area, and root volume, were significantly different from other treatments, which were 112.82%, 79.89%, 101.21%, and 102.53% higher than CK, respectively. With the increase of straw and its biochar addition ratio, the root fractal dimension of each treatment gradually increased, from 1.425 in CK to 1.514 in T3, and the topological index gradually decreased, from 0.699 in CK to 0.628 in T3, the topological index of T3 was closer to 0.5. The maize root biomass and main morphological parameters had very significantly positive correlations with fractal dimension and fractal abundance, and very significantly negative correlations with topological index.

Conclusion The addition of straw and its biochar can effectively improve the physical and chemical properties of the substrate and provide a high-quality growth environment for the root system. The environment has a high plasticity for root architecture, the change of the physicochemical properties of the matrix can make the maize root architecture tend to change in a direction that is more conducive to nutrient and water utilization. The root architecture traits can characterize the morphological characteristics of the root system to a certain extent, and can also be used as an index to verify the cultivation effect of the composite substrates.