Alfalfa (Medicago sativa L.) is an important perennial legume forage that is cultivated in saline soil worldwide. This study aimed to clarify the effects of organic base fertilizer and inorganic topdressing on the productivity of alfalfa growing in saline soil. A three-year field study was conducted in which alfalfa was grown in the saline soil of the Huanghe River Delta with a control (no fertilizer) and three treatments: organic base fertilizer (Base), topdressing with urea fertilizer (Top), and combined base and topdressing fertilizers (BT). The productivity in the BT and Base treatments was 13.21 and 13.82 t·hm⁻² in 3 years, significantly higher than that in the Top treatment and the control. The increased productivity in the BT and Base treatments were because organic matter promoted root growth of alfalfa seedlings in saline soil. The diversity of the soil bacterial community was not affected by the BT treatment, but the Base treatment increased the abundance of Acidobacteria, and the Top treatment increased the abundance of Gemmatimonadetes. Soil bacteria play an important role in improving the productivity of alfalfa growing in saline soil, and the mechanism by which soil microbes increase yield needs to be further studied.

Combined stress from water and temperature is considered an effective approach for improving the cold resistance of alfalfa (Medicago sativa L.). However, the relationships among irrigation depth, root morphology and architecture, and cold resistance of alfalfa remain unclear. In this study, we investigated the effects of drip irrigation at the soil surface (Deep-0), at 20 cm depth (Deep-20), and at 40 cm depth (Deep-40) on root morphology and architecture and cold resistance of alfalfa. The Deep-0 treatment had the highest aboveground biomass and belowground biomass, and the root system in the Deep-40 treatment tended to a ‘herringbone’ branching type, which increases the cost of water uptake. After cold acclimation for 3 days, the cold resistance of Deep-0 was strongest, and was associated with higher soluble sugar content and fewer reactive oxygen species in the roots. Deep-40 enhanced the severity of drought stress on the crown and increased the risk of crown exposure to low-temperature stress. The results showed that Deep-0 promoted alfalfa growth and development by regulating root morphology and architecture and improving water absorption efficiency, thereby enhancing the ability of the root system to withstand low-temperature stress.