Effects of alternate furrow irrigation on the biomass and quality of alfalfa (Medicago sativa)

Alternate furrow irrigation is considered a water-saving technique to improve water use efficiency without considerable yield reduction in horticultural crops and field crops. We investigated the effects of alternate furrow irrigation on the biomass and quality of alfalfa (Medicago sativa) in this study. A field experiment was designed with two irrigation modes (alternate furrow irrigation-AFI and conventional irrigation-CI) and four irrigation volumes (70%-I1, 85%-I2, 100%-I3 and 115%-I4 of alfalfa water requirement (ET)). Alternate furrow irrigation increased the water use efficiency based on the total biomass and aboveground biomass of alfalfa by 40-46% and 36-42%, respectively. This approach maintained comparable aboveground biomass at the first and the second harvest times but significantly decreased the aboveground biomass at the third harvest time, which contributed to the seasonal drop in aboveground biomass compared to conventional irrigation. Alternate furrow irrigation increased the number of branches per plant, but decreased the leaf numbers per plant at the first harvest time and the plant height at the second harvest time. This trade-off was comparable to the aboveground biomass at the first and the second harvest times compared to conventional irrigation. Meanwhile, the reduction in plant height and leaf numbers per plant caused by alternate furrow irrigation at the third harvest time contributed to the aboveground drop in biomass. The results also demonstrated that alternate furrow irrigation increased the root biomass and root volume, which reduced the ratio of aboveground biomass to root biomass and decreased the stem-to-leaf ratio compared to conventional irrigation. Our findings indicate that alternate furrow irrigation not only increases the water use efficiency of alfalfa without trading off aboveground biomass before the second harvest time but also improves the forage quality of alfalfa in the study region.