Evaluating the Forage Production Potential of Sorghum Promising Lines (Sorghum bicolor (L.) Moench) at Different Reproductive Growth Stages

Abstract
In recent years, attention to sorghum has increased due to its high forage production potential and drought tolerance in many regions of the world. Since the yield and quality of this plant's forage are influenced by the growth stage, this study was conducted to examine the effect of harvest time on the quantitative and qualitative traits of sorghum forage. The experiment was carried out in a factorial arrangement within a randomized complete block design with three replications in Karaj. The experimental factors included harvest time at four levels (milk stage, soft dough stage, hard dough stage, and grain physiological maturity) and promising sorghum lines at seven levels. The maximum protein and digestible organic matter yields (22.64 and 17.98 ton.ha^-1, respectively) and the highest production of metabolizable energy (65.44 Gcal.ha^-1) were obtained at the grain physiological maturity stage, whereas the highest protein content and organic matter digestibility (9.2% and 62.9%, respectively) and the maximum metabolizable energy content (2.35 Mcal.kg^-1) were recorded at the grain milk stage. Furthermore, with increasing plant age, the amount of prussic acid, water-soluble carbohydrates, ash, and ether extract decreased, while the contents of fiber and organic matter increased. Among the genotypes studied, the highest quantitative and qualitative yield and the minimum prussic acid content were observed in the promising line MDFGS1. As maturity progressed from the milk stage to physiological maturity, the quantitative yield increased while forage quality decreased. Overall, to achieve suitable quantitative and qualitative yields, it is recommended to harvest sorghum forage at the soft dough stage. Furthermore, the promising line MDFGS1 is recommended as the superior genotype.
Introduction
In recent years, attention to sorghum has increased in many regions of the world due to its high potential for forage production and drought tolerance. In the domain of forage production, the significance of forage quality extends beyond dry matter considerations. The quality of forage holds paramount importance, as it serves as an indicator of its nutritional value and energy content, directly influencing the quantity of nutrients that animals can efficiently acquire from the forage within the most efficient timeframe. Since the forage yield and quality of this crop is affected by the growth stage, this study was conducted to evaluate the effect of harvesting time on quantitative and qualitative traits of sorghum forage.
Materials and Methods
The experiment was conducted as a factorial design based on a randomized complete block design with three replications at the Research Field of Seed and Plant Improvement Institute, Karaj, Iran (35°47'N, 50°54'E; 1248 m a.m.s.l.) with a semi-arid environment. The experimental factors included the harvesting time at four levels (milk, soft dough, hard dough, and grain physiological maturity) and the sorghum promising lines at seven levels (KDFGS4, KDFGS6, KDFGS9, KDFGS16, KDFGS26, MDFGS1, and MDFGS2. Data were analyzed using PROC GLM (general linear model) of SAS 9.1 software. The means comparison was conducted utilizing Tukey's test at a significance level of 5%.
Results and Discussion
The maximum protein and digestible organic matter yields (2.64 and 17.98 ton ha^-1, respectively) and the highest production of metabolizable energy (65.44 Gcal ha^-1) were obtained at the grain physiological maturity, whereas the highest protein content and organic matter digestibility (9.2 and 62.9%, respectively) and the maximum metabolizable energy content (2.35 Mcal kg^-1) were recorded at the grain milk stage. Furthermore, with increasing plant age, the amount of prussic acid, water-soluble carbohydrates, ash, and ether extract decreased, and the contents of fiber and organic matter increased. Among the studied genotypes, the highest quantitative and qualitative yield and the lowest prussic acid content were observed in the promising line MDFGS1. With progress toward maturity from the milk stage to physiological maturity, quantitative yield increased and forage quality decreased.
Conclusions
Overall, it is recommended to harvest sorghum forage at the soft dough stage to achieve a suitable quantitative and qualitative yield. Furthermore, the promising line MDFGS1 could be introduced as the superior genotype.
Acknowledgements
This research was supported by the Seed and Plant Improvement Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran [Project number 03-03-0313-043-960461]. The authors are thankful for providing laboratory facilities and all technical support in the experimental field.