Soil amendment with a humic substance and arbuscular mycorrhizal Fungi enhance coal mine reclamation

Coal mine sites covered by sandy soils often have low nutrient and high heavy metal concentrations, making reclamation for agricultural uses challenging. Although the combined use of humic substances and soil biota has generated considerable research interest, little information is available regarding their synergistic effects. In a two year field study, we assessed the effects of sole and combined applications of a humic substance product called nano humus (150 g/m2 in soils), arbuscular mycorrhizal fungi (250 g inocula/m2 in soils), and fertilizer (37 g/m2 in soils) on soil chemical properties, soil heavy metals, and growth of alfalfa (Medicago ruthenica L.) and barley (Hordeum vulgare L.). Application of arbuscular mycorrhizal fungi with nano humus exhibited greatest effects in year two. Relative to untreated soils, they increased soil cation exchange capacity by 38%, total organic carbon by 36%, and available nitrogen, phosphorus, and potassium by 20 to 92%; they reduced concentrations of soil cadmium by 25% and of arsenic by 9%. Mycorrhizal colonization rate and soil heavy metal concentrations were significantly negatively correlated, suggesting an inhibition effect of metals on colonization. The combination of arbuscular mycorrhizal fungi and nano humus showed greatest impact on root and shoot biomass of alfalfa, which increased 18 and 12 times, respectively. Barley responded most positively to combinations of arbuscular mycorrhizal fungi, nano humus, and fertilizer; root biomass increased 4 times, and shoot biomass and seed production increased 3 times. Combined applications generally provided greater benefits than sole applications, which could be a useful practice in heavy metal contaminated reclamation sites.