Response of alfalfa nutritional quality to fall dormancy level and harvest time in the coastal alkali-saline region of Hebei Province

Alfalfa (Medicago sativa L.) is an important forage crop with high protein content. Alfalfa cultivation is a predominant method for high-efficiency utilization of saline-alkali land and can help ensure feed grain security. Alfalfa productivity in coastal saline-alkali land is typically constrained by factors such as freshwater shortage and high salinity levels, leading to a decrease in the nutritional quality of alfalfa forage. Although alfalfa yield did not show a strong relationship with fall dormancy type in moderate climatic regions, nutritive quality could be correlated. Reasonable harvest management is integral to achieving a high forage quality in alfalfa. Therefore, the aim of the current study was to explore the effects of fall dormancy types, harvest times, and their interaction on forage quality in saline-alkali soils. A field experiment was conducted in the coastal saline-alkali region of Hebei Province. The treatments comprised five fall dormancy types with 40 alfalfa cultivars (extreme fall dormancy, fall dormancy, semi-fall dormancy, non-fall dormancy, and extreme non-fall dormancy) and six harvest times. We found that the following results: 1) The total annual yield of crude protein (CP) was significantly affected by fall dormancy type and harvest time (P<0.05). The highest total annual CP yield was obtained in the extreme fall dormancy treatment and was 14.5% higher than that in the semi-fall dormancy treatment. The CP yield of the fifth harvest differed significantly among different fall dormancy types, whereas the fall dormancy type had no obvious effects on the CP yield of crude protein at other harvest times. 2) The CP content initially increased and then decreased with increase in harvest time. Fall dormancy had a significant effect on CP content at the sixth harvest, when the highest value for CP content (21.5%) was observed in the extreme fall dormancy treatment and was higher than that in the non-fall dormancy treatment. 3) After the first harvest, the fall dormancy type had significant effects on neutral detergent fiber (NDF). The highest NDF was observed in the extreme fall dormancy type. Fall dormancy type had no significant effect on acid detergent fiber (ADF). 4) Relative forage value (RFV) differed significantly across fall dormancy types and harvest times. The highest RFV was observed at the fourth harvest. The RFV of the first harvest of the extreme non-fall dormancy (165.3) was higher than that of the extreme fall dormancy. Overall, we found that fall dormancy type and harvest time had significant effects on alfalfa nutritional quality in the coastal alkali-saline region, with these effects especially strong in the first and final harvests at low temperatures. Combining the CP yield and relative feeding value, alfalfa with higher fall dormancy levels is an important source of feed from the second to the fourth harvest in the coastal alkali-saline region. To achieve high-quality alfalfa yields in the coastal alkali-saline region of Hebei Province, the effects of fall dormancy type and harvest time on the nutritive quality of alfalfa must be considered.