Effects of nitrogen addition and intercropping patterns on agronomic traits of oats and peas in alpine regions

Few studies have focused on the effects of intercropping and nitrogen addition on the agronomic traits of oat (Avena sativa) and pea (Pisum sativum) in intercropping systems in alpine regions. Therefore, this study used a new oat line ‘Qingyong jiu 872’ and forage pea (‘Qingjian 1’) as experimental objects to compare the effects of intercropping patterns and nitrogen addition on the regulation of key agronomic traits and yield of oats and peas. The results showed that cropping patterns and nitrogen addition affected agronomic traits of oats and peas. The total land equivalent ratio of oat and pea cropping systems was highest under low N addition and intercropping, and the interspecific competitiveness of oat was stronger than that of pea under the N addition levels N₂ (50 kg·ha⁻¹) and N₃ (200 kg·ha⁻¹). Redundancy Analysis (RDA) showed that planting pattern and nitrogen addition level were positively correlated with agrological traits related to grass yield, such as oat plant height and number of tillers per plant, whereas nitrogen addition level was positively correlated with agrological traits related to pea forage yield. Furthermore, the planting pattern was positively correlated with agrological traits related to pea seed yield. Grey correlation analysis showed that when nitrogen was not added i.e., N₁ (0 kg·ha⁻¹), the monocropping oat number of tillers and pea first pod nodes per plant, alternate-row intercropping oat number of seeds and pea number of pods per plant, and mixed intercropping oat number of tillers and pea number of pods per plant showed the highest correlation with forage yield. Under low nitrogen addition level i.e., N₂ (50 kg·ha⁻¹), monocropping oat number of tillers and pea number of seeds per plant, alternate-row intercropping oat grain length and pea number of pods per plant, and mixed intercropping oat number of spikelets and pea number of seeds per plant showed the highest correlation with forage yield. Under high nitrogen addition level i.e., N₃ (200 kg·ha⁻¹), monocropping oat stem thickness and pea number of pods per plant, alternate-row intercropping oat seed weight and pea number of seeds per plant, and mixed intercropping oat number of seeds and pea number of pods per plant showed the highest correlation with forage yield. Therefore, the reasonable arrangement of the planting pattern and precise nitrogen application have become key to high-quality grassland cultivation in alpine regions.