1. Barneix H J and Arnozis P A 1980 Effect of nitrate and ammonium on phosphate absorption by wheat seedlings. Øyton 39, 7–13.
2. Brown R W, Schultz R C and Kormanik P P 1981 Response of vesicular-arbuscular endomycorrhizal sweetgum seedlings to three nitrogen fertilizers. Forest Sci. 27, 413–420.
3. Chambers C A, Smith S E and Smith F A 1980 Effects of ammonium and nitrate ions on mycorrhizal infection nodulation and growth ofTrifolium subterraneum. New Phytol. 85, 47–62.
4. Coxwell M J 1983 Effects of nitrogen source and levels on vesicular-arbuscular mycorrhizal colonization, growth and chemical composition ofPittosporum tobira Thunb. M.S. Thesis, University of Florida, Gainesville.
5. Dogar M A and Van Hai T 1979 Influence of ammonium concentration on uptake and content of P, K, Ca and Mg in rice grown in solution culture. Z. Pflanzenphysiol. 93, 273–280.