Abstract:

It would be beneficial to the livestock industries to develop and utilize the potential for improved forage quality and yield in alfalfa in order to achieve gains in production efficiency. This study planned to establish a nitrogen （N） efficiency evaluation system and screen alfalfa germplasm at the seedling stage for N efficiency. In this research， 28 alfalfa cultivars from a wide range of sources were investigated， and parameters linked to alfalfa N efficiency were evaluated at the seedling stage， based on variation coefficient， correlation analysis and subordinate function analysis of the morphological and N-related parameters. Seedlings were grown in sand culture in a greenhouse using nutrient solution with either a low N level （2.1 mg·L^–1 N， designated N_2.1） or a normal N level （210 mg·L^–1 N， designated N₂₁₀）. N efficiency was assessed from the multivariate response of cultivars to N application. It was found that the plant height， shoot dry weight （SDW）， root dry weight， plant dry weight （PDW）， shoot N accumulation （SNA）， root N accumulation and plant N accumulation （PNA） of LW6010 were significantly higher than other cultivars. The SDW of Gongnong No.3 was significantly lower than that of other cultivars under both N_2.1 and N₂₁₀. The shoot N content and plant N content of Giant 601 were significantly higher than those of other cultivars. Under N_2.1， the root length （RL） of Gannong No.9 was the longest， and that of Longdong was the shortest. Under N₂₁₀， the RL of Crown is the longest， and Gongnong No.3 is the shortest. Under N_2.1， the root volume （RV） of Xinjiangdaye was the largest， and that of Longdong was the smallest. Under N₂₁₀， the RV of Gannong No.7 was the largest. The parameters used to screen for N efficiency were SDW， PDW， RL， RV， SNA and PNA. The multivariate scores of LW6010 and some other cultivars were greater than 0.5 under N_2.1 and N₂₁₀； the multivariate scores of Gannong No.3 and some other cultivars were less than 0.5 under N_2.1， and were greater than 0.5 under N₂₁₀. The multivariate scores of Gannong No.7 and some other cultivars were greater than 0.5 under N_2.1， and were lessr than 0.5 under N₂₁₀； and those of Longdong and some other cultivars were less than 0.5 under N_2.1 and N₂₁₀. In conclusion， differences in N efficiency among alfalfa cultivars were found. SDW， PDW， RL， RV， SNA and PNA were adopted as the evaluation parameters for N efficiency screening of alfalfa at the seedling stage. By quantifying the multivariate score， alfalfa cultivars can be grouped into four N efficiency categories： very efficient， efficient， semi-efficient and inefficient.

Key words: Medicago sativa, N efficiency, differences of cultivars, characteristics of N efficiency types