Spatial heterogeneity in biomass yield and quality driving regional strategies for enhanced rice straw bioeconomic potential: a case study in Hunan, China.

As China's leading rice-producing province (>4 million ha annually), Hunan generates a large amount of straw residue, yet inefficient utilization causes significant resource waste and environmental impacts. Establishing diversified industrial clusters for high-value biomass conversion presents a critical solution. Understanding regional differences in rice straw yield potential and quality is crucial to develop the well-designed industrial clusters layout. This study explores spatial variations in rice straw yield and quality across Hunan, where 37.03 Mt of rice straw are produced annually. Central and northern Hunan account for the majority of production, contributing 12.67 Mt (34.22 %) and 8.71 Mt (23.52 %), respectively. Biomass quality exhibited pronounced spatial heterogeneity, with coefficients of variation (CVs) exceeding 0.4 for all indicators. Heavy metal content (Cd, Cr, Cu, Mn) showed the highest variability (CV of 9.26, 6.19, 6.66, 5.87, respectively), followed by ash content (CV = 1.93), degree of cellulose polymerization (DP, CV = 1.83), and lignin content (CV = 1.03). Such variability critically influences bio-product selection: elevated heavy metals necessitate costly purification for food/feed-grade applications, while low DP and crystallinity reduce pretreatment costs for cellulose-based products. Geographical location, soil properties, and climatic conditions collectively explained 60.28 % of the variation in rice straw quality, while only 1.76 % was attributable to variety. Within Hunan Province, rice straw demonstrates optimal suitability for producing hemicellulose-based products, especially from central Hunan, which has a calculated production index of 0.54. Central Hunan is thus identified as a pilot zone for establishing rice straw-based industries, given its yield potential and biomass quality variation.