Organic fertilizer altering root trait and microbial composition to promote the compactness tolerance of peanut

Continuous cultivation and excessive chemical fertilizer use have led to increased soil compaction in peanut (Arachis hypogaea L.) fields, significantly hindering plant growth and development. Organic fertilizer can improve soil nutrient content, aeration, and overall soil environments, thereby promoting healthy plant growth. However, the mechanisms underlying the effects of substituting chemical fertilizer with organic fertilizer on peanut growth under compaction stress are still elusive. To investigate the responses of peanut root traits, soil physicochemical properties, and microbial community structure to organic fertilizer substitution under soil compaction, a pot experiment was conducted using two compaction levels (1.2 and 1.6 g/cm³) and three organic fertilizer rates (0, 120, 240 g/pot) in Laixi, Shandong Province, a major peanut producing area. Results showed that organic fertilizer significantly improved plant biomass, height, stem diameter, and nodule fresh weight during the flowering and podding stages. Root traits including total root length, total surface area, and root volume, were significantly increased, especially at the podding stage (p < 0.05). The number of xylem vessels increased under 1.2 g/cm³ compaction but showed no significant change under 1.6 g/cm³. Soil available phosphorus and potassium contents increased with higher fertilizer rates. Distance-based redundancy analysis (RDA) showed that rhizosphere bacterial and fungal communities were affected by soil physical and chemical properties. Partial least squares path modeling (PLS-PM) indicated that soil organic matter was positively correlated with soil enzyme activity, which indirectly enhanced fungal diversity, while bacterial diversity showed negative correlation with soil organic matter. In conclusion, applying organic fertilizer in accordance with soil compaction levels offers an efficient strategy to improve soil microbial structure, enhance soil fertility, and promote peanut growth under compacted field conditions.