Root, Yield, and Quality of Alfalfa Affected by Soil Salinity in Northwest China

Growing crops in salt-affected soils has become increasingly important for sustainable development in arid and semi-arid regions. Knowledge on the responses of alfalfa root development, yield, and quality to soil salinity is critical for assessing the productivity and profitability of salt-affected soils. A field experiment with a total of six treatments combining three soil salinity levels and two biosolids fertilizer levels was conducted in 2018 and 2019 in northwest China. For salinity treatments, the salt addition rates were 2‰, 4‰, and 6‰ of 0–60 cm soil dry weight, while a commercial biosolids fertilizer was added at a rate of 0 and 1.5 Mg·ha −1 of 0–10 cm soil for biosolids treatment. Root parameters of root length (RL), surface area (RSA), diameter (RD), volume (RV), and dry matter (RDM) were obtained at the end of each year, while yield and quality parameters of crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF) were measured for each cut of the two years. Most root parameters were significantly reduced by the highest soil salinity treatment in 2018, but not affected by salinity in 2019. Higher salinity treatments consistently led to lower plant height and yield, higher CP, and lower ADF and NDF in both years. The absolute slope value of the regression between yield of each cut with the respective soil salt content was smaller for the later cuts. The relationship between plant height and quality parameters varied depending on soil salinity levels and between the two years, and plant height was found to be a good predictor for alfalfa quality in 2019. Biosolids fertilizer had no significant effect on any alfalfa root, growth, or quality parameters. The results are expected to assist determining the proper soil salinity range, maximizing the productivity that takes both yield and quality into consideration.