Influences of arbuscular mycorrhizae, phosphorus fertiliser and biochar on alfalfa growth, nutrient status and cadmium uptake.

The objective of the study was to explore the influences of arbuscular mycorrhizae (AM), phosphorus (P) fertiliser, biochar application (BC) and their interactions on Medicago sativa growth, nutrient, Cd content and AM fungi-plant symbioses. Applications of both P fertiliser and BC significantly increased total biomass and P and potassium (K) uptake, regardless of AM. When no P fertiliser or BC was used, the shoot biomass and nitrogen (N), P, and K contents in the +AM treatments were 1.39, 1.54, 4.53 and 2.06 times higher than those in the -AM treatments, respectively. AM fungi only elevated the total P uptake by 44.03% when P fertiliser was applied at a rate of 30 mg P kg-1 in the absence of BC addition. With BC application or high-P fertiliser input (100 mg P kg-1), the soil available P was significantly higher than that in the other treatments, and AM fungi significantly reduced the shoot biomass. The minimum Cd concentration occurred in the shoots of alfalfas treated with BC and high-P fertiliser inputs; this concentration was lower than the maximum permitted concentration in China. Although the BC and high-P inputs could eliminate the positive mycorrhizal response, the results suggested that BC application in combination with high-P fertiliser input could not only increase forage yields but also lower Cd concentrations to meet the forage safety standards by the dilution effect.