Interactions between humic substances and organic amendments affecting soil biological properties and growth of Zea mays L. in the arid land region

Application of organic amendments to the arid land soils is a sustainable tool to improve soil fertility. A greenhouse experiment was conducted to find the effect of humic acid (HA), alfalfa residues (AR) (Medicago sativa L.), and sheep manure (SM) on soil respiration, soil organic carbon content, soil structure, total bacteria, total fungi, and growth of corn plant Zea mays L. Results showed that the highest aggregate stability was 44.2% for the HA + SM treatment whereas it was 9% for the HA treatment. The higher stability was associated with higher organic carbon 4.60%, and higher bacterial and fungal densities of 190 × 10 ⁶ g ⁻¹ dry soil and 101 × 10 ⁶ g ⁻¹ , respectively. The HA + AR treatment did not increase aggregate stability significantly (27.7%), nor did the AR treatment (25.9%). Soil respiration over 70 days was significantly (p < 0.05) higher in the SM (42.9 CO ₂ –C mg g ⁻¹ ) compared to the AR treatment (33.3 CO ₂ –C mg g ⁻¹ ). In contrast, the HA + SM treatment had lower soil respiration (27.4 CO ₂ –C mg g ⁻¹ ) compared to the SM treatment (42.9 CO ₂ –C mg g ⁻¹ ). The HA + AR treatment recorded higher plant weight (20.6 g) compared to HA (10.2 g) and control treatments (8.11 g). This study proved that HA did not enhance soil structure or the microbial community, whereas the combination of HA with SM or AR is more effective at promoting the soil microbial community, soil aggregation, organic carbon content and plant growth in the saline, arid land.