Effects of NO_3~--N and NH_4~+-N on root growth,nodulation and nitrogen-fixation of alfalfa

The sand culture with nutrient solution was used to study the effects of NO-3-N and NH+4-N on root growth,root activity,above and under-ground nitrogen content,nodule number and nitrogenase activity of alfalfa(cv.Gannong 3).The results showed that root and nodule growth,root activity,shoot and whole plant nitrogen content,nitrogenase activity grown in NH+4-N nutrition showed better than those grown in NO-3-N.Root activity,nodule number and nitrogenase activity of alfalfa inoculated with rhizobia that grown under different nitrogen forms were found higher than un-inoculated alfalfa plants.Root volume,root dry weight,effective nodule number and nitrogenase activity of inoculated and un-inoculated alfalfa supplied with nitrogen were found higher than those N-free plants.According to the comparison of the two rhizobia,root activity,total nitrogen content of different parts of the plants,nodule number and nitrogenase activity of alfalfa inoculated with 12531 performed better than alfalfa inoculated with LW107 in both N and N-free environment.It is suggested that the ability of nodulation and nitrogen fixation of alfalfa inoculated with 12531 and grown in NH+4-N is better.