Effects of Elymus sibiricus and Medicago sativa intercropping on pasture soil C, N, and P stoichiometric characteristics

In this study, Medicago sativa (alfalfa) and Elymus sibiricus grasslands in the third year of different intercropping ratios (2 ꞉ 4, 2 ꞉ 5, 2 ꞉ 6, 2 ꞉ 7, and 2 ꞉ 8) were used as experimental subjects. The carbon (C), nitrogen (N), and phosphorus (P) contents and stoichiometric characteristics in forage soil were studied to explore the conversion and utilization characteristics of each component in the five intercropping treatments to reveal the optimal intercropping ratio and its growth limiting factors. We found that the competition ratios of C, N, and P of E. sibiricus to alfalfa were less than one in intercropping treatments, i.e., alfalfa had a stronger nutrient competition ability than E. sibiricus. The C content of alfalfa was significantly different from that of the E. sibiricus monoculture, and that of the 2 ꞉ 4 intercropping treatment increased significantly by 17.35% (P < 0.05), whereas the C content of E. sibiricus under the 2 ꞉ 7 and 2 ꞉ 8 intercropping treatments increased significantly by 5.39% and 1.62% (P < 0.05) compared with the E. sibiricus monoculture, respectively. Under the 2 ꞉ 7 intercropping treatment, the N content of alfalfa and E. sibiricus were higher, increasing significantly by 20.08% and 6.83% compared with that of the E. sibiricus monoculture (P < 0.05). Furthermore, the alfalfa C ꞉ N decreased significantly by 12.32% (P < 0.05), N ꞉ P increased significantly by 18.48%, and the N ꞉ P and C ꞉ P of E. sibiricus increased significantly by 27.63% and 25.86% compared with the ratio of the E. sibiricus monoculture (P < 0.05), respectively. The C ꞉ N under the 2 ꞉ 4 intercropping treatment decreased significantly by 18.56% (P < 0.05) compared to that of the monoculture. Soil total N content, total P content, and N ꞉ P were not significantly different between treatments, whereas soil organic C and C ꞉ N increased significantly by 0.3-folds and 1.2-fold compared to the alfalfa monoculture under the 2 ꞉ 6 intercropping treatment (P < 0.05). Redundancy analysis showed that both forage and soil were limited by N and 2 ꞉ 7 intercropping treatment was more effective to alleviate N limitation.