Influence of inorganic N on mycorrhizal activity, nodulation, and growth ofLeucaena leucocephalain an oxisol subjected to simulated erosion

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Abstract
The influence of inorganic N on the development of mycorrhizal symbiosis in Leucaena leucocephala (Lam.) de Wit was sudied in an Oxisol subjected to simulated erosion. The plants were grown in pots containing soil samples inoculated with the VAM fungus Glomus aggregatum and amended with 0, 25, 50 or 100 ppm N. The extent of VAM colonization of roots increased with increasing levels of N in both eroded and uneroded soils. However, the level of infection was significantly higher in the eroded soil than in the uneroded one. Mycorrhizal activity monitored in terms of P conent of leucaena subleaflets increased significantly in the eroded soil when it was amended with 25 ppm N and became similar to that observed in the uneroded soil. Nodule dry matter production and shoot N concentration increased significantly with N application upto 50 ppm. Above this level of N, nodule dry weight declined while N concentration did not change. Application of 25 ppm N to the eroded soil also significantly increased shoot and root dry weights while no change was observed in the uneroded soil. A further increase in N level did not improve yield. The results illustrate the potential benefits of starter N in the establishment of mycorrhizal and nodulated Leucaena leucocephala in eroded soils.