Abstract:We used the seedings of 22 wild loquat (Eriobotrya japonica Lindl.) germplasm from Guizhou Karst area as the test materials in the experiment, and the method of soil culture and nutrient solution culture experiment in this study. The plant height, and dry weight, nitrogen content, absorption amount and uptake efficiency of NH+4N, nitrogen use efficiency, maximum uptake rate (Imax) of NH+4, the Michaelis constant value (Km), the flow rate of NH+4 into root (α) of 22 wild loquat germplasm seedlings under different NH+4N levels were tested. The difference, interaction and correlation between the above indexes were analyzed and evaluated,and nutrition efficiency type of different wild loquat germplasm was divided. The results showed that: (1) the dry weight of seedlings, nitrogen absorption amount and nitrogen efficiency in different germplasm and NH+4N levels were significantly different. The coefficient variation (CV) of seedlings dry weight, nitrogen content, absorption amount and uptake efficiency of NH+4N,and nitrogen efficiency were 21.09% and 16.87%, 17.06% and 20.00%, 36.67% and 40.21%, 36.71% and 40.24%, 21.05% and 19.21%, respectively among 22 wild loquat germplasm seedlings. The difference of NH+4 absorption kinetic parameters among different wild loquat germplasm were very obvious. The CV of Imax, Km and α under high nitrogen and low nitrogen levels were 44.64% and 60.00%, 73.53% and 81.48%, 89.58% and 109.18%, respectively. (2) Among all the above indicators, the differences and interactions in different germplasm and two NH+4N levels were extremely significant (P <0.01), the dry weight of seedlings, nitrogen content, absorption amount and uptake efficiency of NH+4N, nitrogen efficiency, Imax and α of NH+4 all had extremely significantly positive correlation of 22 wild loquat germplasm, while the Km was extremely significantly negative correlation to above indexes. Under high nitrogen and low nitrogen levels, the direct path coefficient of NH+4N absorption efficiency to nitrogen efficiency was the largest (1.805 and 1.523), and the direct contribution was also the most. (3) Through the above filter, 22 wild loquat germplasm were classified into four nitrogen efficiency types: efficient under high nitrogen and low nitrogen, efficient under high nitrogen, efficient under low nitrogen and inefficient under high nitrogen and low nitrogen. There were 7, 4, 2 and 9 germplasm, respectively. The studies showed that the different of uptake and use efficiency for ammonium nitrogen among 22 wild loquat germplasm of Guizhou Karst area were significantly different. The dry weight of seedlings, absorption amount and uptake efficiency of NH+4N, and nitrogen efficiency can be used as evaluation and filter indexes of nitrogenefficient loquat germplasm.