Enhancement of Endomycorrhizal Activity through Nitrogen Fertilization in Cowpea Grown in an Oxisol Subjected to Simulated Erosion

The influence of inorganic nitrogen on the development of mycorrhizal symbiosis in Vigna unguiculata (L.) Walp cv. California Blackeye No. 5 ( cowpea) was studied in a noneroded oxisol and an oxisol subjected to simulated erosion. Plants were grown in pots containing soil inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus aggregatum and amended with 0-100mg N kg(-1) soil. Vesicular-arbuscular mycorrhizal colonization of roots, shoot P and N status, and shoot, root, and nodule dry weights were significantly stimulated by amendment of the eroded soil with N. However, the response of root colonization, shoot P concentration, and nodule dry weight to N application of the noneroded soil was not significant. The relationship of N with root colonization and shoot P status was described by a linear model while the relationships between N and other variables measured were described by quadratic equations. The results illustrate the potential benefits of starter N in the establishment of mycorrhizal and nodulated cowpeas in eroded soils.