Selecting Fore and Succeeding Crops to Construct a Double-Cropping System That Increases the Forage Yields of Alpine Pastoral Areas on the Qinghai–Tibetan Plateau

Double-cropping systems in which two kinds of crops are harvested per year can elevate forage yields significantly. This is the first report on a double-cropping system in the northeastern margin of alpine pastoral areas on the Qinghai–Tibetan Plateau with an elevation of 3500 m. In this experiment, eight triticale genotypes, including five varieties (‘Gannong No. 2’, ‘Gannong No. 3’, ‘Gannong No. 4’, ‘Gannong No. 7’, and ‘Zangsi No. 1’), and three lines (C16, C23, and C25) were used as the fore crops, with the four succeeding crops being 50% of triticale mixed with 50% of forage pea (B1), 50% of triticale mixed with 50% of common vetch, 50% of oat mixed with 50% of forage pea, and 50% of oat mixed with 50% of common vetch. Over 2 years (2020–2021), among the fore crops, ‘Gannong No. 4’ had the highest average hay yield (9.00 t·ha−1), crude protein content (114.97 mg·g−1), and relative feeding value (91.77), as well as the lowest average neutral detergent fiber content (598.17 mg·g−1). Among the succeeding crops, B1 had the highest average hay yield (11.45 t·ha−1) and nutritional quality. Among the interactions between the fore and succeeding crops, the highest hay yield (21.72 t·ha−1), crude protein content (262.22 mg·g−1), and relative feeding value (219.34) were obtained when ‘Gannong No. 4’ was doubled with B1. The results provide a theoretical basis for carrying out a double-cropping system in the alpine pastoral areas on the Qinghai–Tibetan Plateau, and this has very important implications for crop production in this area.