Introduction: Due to the increasing demand for animal protein resources on the one hand and the lack of available water resources on the other, it is crucial to investigate the forage potential of plants for animal nutrition. The Jerusalem artichoke, which is primarily grown for its tubers, produces a substantial amount of forage-worthy aerial parts. However, few studies on the aerial portion of this plant have been conducted in Iran, and those that do exist were conducted at the Research Institute of Animal Sciences in Alborz province. Consequently, the present study was conducted to determine the variations in yield, chemical composition, and digestibility of the Jerusalem artichoke aerial part and its constituents at various growth stages over two consecutive years.
Materials and Methods: To examine the variations in yield and quality of the aerial portion of Jerusalem artichoke, a randomized complete block experiment with 4 replications was conducted in the Agricultural Research Station of Razi University over the course of two consecutive years, 2018 and 2019. From the vegetative stage to full flowering, the yield and yield components (at 7 stages) and chemical composition and digestibility (at 5 stages) of the aerial part of the plant were determined. The chemical composition was determined includes organic matter, ash-free cell wall fibers, water-soluble carbohydrates, and crude protein. In addition, the digestibility of samples whose chemical compositions were measured was determined invitro using two stages of anaerobic digestion and acidic pepsin digestion.
Results and Discussion: In the first and second years, the dry matter yield of Jerusalem artichoke aerial part at two stages of just before flowering and full flowering was 29.1 and 30.4 tons per hectare and 24.0 and 25.3 tons per hectare, respectively. Increased dry matter accumulation in the stem was associated with increased yield during growth stages. These alterations were associated with an increase in height and a decrease in leaf: stem ratio. The ratio of leaf to stem decreased from 1.62 to 0.41 in the first year and from 1.50 to 0.61 in the second year between the vegetative stage and full flowering. In the present study, the increase in aerial organic matter with increasing plant age was due to an increase in stem yield and an increase in its organic matter. During the growth stages, the stem contained more organic matter, insoluble fibers in neutral detergent, and soluble carbohydrates, while the leaf contained more crude protein. Organic matter, insoluble fibers in neutral detergent and acid detergent content, and lignin in the aerial part just before flowering were, respectively, 895.3, 418.7, 310.6, and 85.3 g/kg dry matter over the course of two years of study. With the continuation of the growth period, the water-soluble carbohydrate content increased and the crude protein content decreased to 225 and 92.4 g/kg dry matter, respectively, just prior to flowering. In the aerial portion of the plant, the digestibility of organic matter and dry matter decreased significantly from the vegetative stage to full flowering in the first and second years, respectively, from 64 to 56 and 65 to 59. An increase in cell wall fibers and an increase in the dry matter yield of Jerusalem artichoke aerial part as the plant matured and reached full flowering reduced the digestibility of the forage. However, the yield of digestible organic matter per hectare remained unchanged between the pre-flowering and flowering stages.
Conclusion: The highest dry matter yield of Jerusalem artichoke aerial part was obtained at the full flowering stage, but the digestible organic matter yield per hectare remained unchanged from just before flowering to the full flowering stage.