Common vetch cultivars improve yield of oat row intercropping on the Qinghai-Tibetan plateau by optimizing photosynthetic performance

Sustainable development of livestock production is challenged by the shortage of forage resources on the Qinghai-Tibetan plateau (QTP). Common vetch-oat intercropping is used on the QTP and in other alpine regions to obtain substantial forage yield, but few common vetch cultivars have been evaluated in intercropping systems. A three-year field experiment in the eastern QTP was carried out to compare plant growth, photosynthetic rate (Pn), radiation use efficiency (RUE), aboveground biomass, land equivalent ratio (LER), and competition ratio of oat row intercropping with three new common vetch cultivars (Lanjian No. 1, Lanjian No. 2, Lanjian No. 3) under low-input conditions. Compared to sole cropping at seed densities of 141 and 667 plants m^–2, for common vetches and oats, respectively, alternate row intercropping with each species at half these densities significantly increased the Pn (by 15–19%) of oat, and reduced the Pn (by 12–26%) of common vetch. Moreover, row intercropping significantly increased intercepted photosynthetically active radiation and RUE (by 44%) for oat but significantly decreased these for common vetch (by 34%). Among common vetch cultivars, at both flowering and maturity stages, Lanjian No. 2 (1.21, 1.15) and Lanjian No. 3 (1.27, 1.21) had greater LER than the later-maturing Lanjian No. 1 (1.07, 1.01) when intercropped. Oat row intercropping with Lanjian No. 2 and Lanjian No. 3 increased forage production compared to sole cropping oat or common vetch on the QTP. These findings provide scientific support for common vetch-oat intercropping as a sustainable approach to increasing forage production from cropland in alpine regions.