The effect of harvesting time on some secondary metabolites and metal elements of Alfalfa (Medicago sativa L.)

Fodder plants have been considered due to their bioactive compounds that affect livestock nutrition and their therapeutic potential for humans. Nowadays, in fodder cropping systems, the proper time of harvesting is very important to obtain optimal performance. In order to investigate the effect of different harvesting times (one to eight weeks after initial harvesting)  on the content of some secondary metabolites (phenols, flavonoids, isoflavonoids and alkaloids) and metal elements (zinc, iron, magnesium and manganese) of alfalfa, a study was carried out based on a completely randomized design with three replications. The results showed that the concentration of these metabolites and metal elements changed significantly at different harvest times. So that the amount of total phenols increased by 2.37, 2.29, and 2.24 times in the fifth, sixth, and seventh weeks, respectively, compared to the second week. Also, the amount of total flavonoids increased by 1.89 times in the sixth week compared to the second week. The amount of total isoflavonoids in the sixth week increased by 1.75 times compared to the first week. The amount of total alkaloids in the seventh and eighth weeks compared to the first week was 10.58 and 11.75 times, respectively. Also, the maximum amount of iron element was observed in the fifth and sixth weeks, and the maximum amount of magnesium and manganese elements were observed in the sixth week. The presence of the maximum amount of these phytoestrogens and metal elements in the middle and the end stages (fifth and sixth weeks, respectively) of alfalfa flowering can be an important factor in determining the quality of fodder and determining the yield of the product, and considering their medicinal properties for humans, these stages are the most suitable harvesting times.