What do the sharp sound and rutting of Ai Qing's trolley symbolize? What is the meaning of the first sentence and the second sentence?

Poetry symbolizes the infinite sadness of northern farmers by making a monotonous and harsh "sharp sound that makes the gloomy sky twitch" to the wheelbarrow commonly used by northern farmers. Barren yellow land, cold foothills, winding mountain roads, accompanied by screams from unicycle, outline a dignified, dark, poor and desolate pastoral scenery of the northland, and vividly express the theme of "the sorrow of the northland people"