Determination of forage and silage characteristics of switchgrass (Panicum virgatum L.) cultivars at different harvest stages

This research was carried out in the Research and Application Field of the Faculty of Agriculture at Siirt University, in 2019-2020, to determine the forage yield and quality, and silage quality of switchgrass (Panicum virgatum L.) cultivars in different harvest stages. In the research, a perennial trial area established with 4 replications according to the randomized complete blocks design with the Kanlow, Shelter, Shawnee, BoMaster, Alamo, Trailblazer, Cave in Rock, and Long Island cultivars of switchgrass formed the location of the research. Parcels were designed for the harvest stages by making upper parcellation based on each variety and its recurrence. In the study, in which the cultivar and the harvest stages were handled as the research subject, the pre-flowering, 50% flowering, and full flowering stages were examined as the harvest stages. Accordingly, the main plots were formed from cultivars, the harvest stages formed the sub-plots, and the research was carried out according to the split plots design in randomized complete blocks. In the study, plant height, stem thickness, canopy temperature, chlorophyll content, tiller weight, green herbage and hay yield, crude protein (CP) ratio, CP yield, acid detergent fibre (ADF) ratio, neutral detergent fiber (NDF) ratio and relative feed value (RFV) parameters related to forage yield and quality were examined. Within the scope of silage quality study, physical properties such as odor, structure and color, dry matter (DM) ratio, and chemical properties of silage consisting of pH, lactic acid (LA), acetic acid (AA), butyric acid (BA) and Fleig score (FS) were investigated. As a result of the statistical analyzes made in the research, it was determined that the cultivars and harvest stages had significant effects on almost every parameter examined. As a result of the research, the plant height, stem thickness, canopy temperature, chlorophyll content, tiller weight, green herbage yield, hay yield, CP ratio, CP yield, ADF ratio, NDF ratio, and RFV ranged between 108.4-174.1 cm, 2.65-4.80 mm, 30.1-34.4 oC, 29.3-34.6%, 3.35-12.76 g, 2170.3-5108.6 kg/da, 908.6-2114.6 kg/da, 3.02-5.97%, 52.3-64.7 kg/da, 39.66-45.31%, 75.49-83.44% and 59.82-71.52 as the average of the years and harvest stages. As the harvest stage progresses; plant height, stem thickness, canopy temperature, tiller weight, green herbage and hay yield, CP yield, ADF and NDF ratio increased, while the chlorophyll content, CP ratio, and RFV decreased. The odor score of switchgrass cultivars for which silage was made varied between 12.1-13.9, the structure score between 3.4-4.0, the color score between 1.6-2.0, and the total physical score between 17.2-19.9. In the study, according to the average of years and harvesting stages, DM, pH, LA, AA, BA, and FS values of switchgrass cultivars silages were between 34.3-40.6%, 4.52-4.73, 0.99-1.56%, 0.35-0.63%, 0.056-0.163%, and 85.3-98.2, respectively. According to the total physical score and FS values, the cultivars were in the "very good" quality class. It was determined that silage DM ratio, pH, and FS values increased, while silage color score, LA, AA, and BA ratios decreased depending on the progress of the harvest stage. According to these results obtained under semi-arid climate conditions, switchgrass seems promising as an alternative feed source for livestock due to its high forage yield. In this sense, the Kanlow cultivar, in particular, came to the fore, and cultivars with lowland ecotype (Kanlow, Alamo, and BoMaster) in general became cultivars with higher yield potential. However, the examined cultivars produced low-quality feed in all harvest stages that were the subject of the research. It would be appropriate to make silage in the early stages of vegetation due to the high content of structural carbonhydrates in switchgrass dry matter, which has good silage quality.