Effects of fertilization and harvest period on Pennisetum flaccidum yield and forage quality in the Lhasa River Valley

In this study, we aimed at exploring effective planting methods for achieving high yield and forage quality for Pennisetum flaccidum in Tibet. We implemented four fertilization treatments in the Lhasa River valley: N₀, N₃₀₀, N₆₀₀, and N₉₀₀ (0, 300, 600, and 900 kg·ha⁻¹, respectively). We collected the samples during the heading, milk, and maturation stages to analyze how the different fertilizer application rates and harvest periods affect P. flaccidum dry hay yield, forage quality, and soil nutrients. Our results demonstrated that P. flaccidum hay yield increased with increasing application rate and was significantly higher during the heading and maturation stages compared to the milk stage (P < 0.05). The crude P. flaccidum protein content decreased gradually with the harvest period delay, while the crude ash content exhibited a decreasing trend with an increasing application rate. However, fertilization did not affect significantly the P. flaccidum acid detergent fiber, neutral detergent fiber, crude fat, and acid detergent lignin contents during the different harvest periods (P > 0.05). The total nitrogen content of the soil tended to increase first, then decrease with the increasing fertilization rate during the heading stage. The total phosphorus content of the soil decreased with the increasing fertilization rate and harvest period delay. We registered the best production performance in the case of the N₉₀₀-treated P. flaccidum, followed by the N₆₀₀-treated P. flaccidum, both harvested at the heading stage, although the latter displayed more economic and ecological benefits.