1. AJAYI, O., D. N. MAYNARD, and A. V. BARKER. 1970. The effects of potassium on ammonium nutrition of tomato (Lycopersicon esculentum Mill). Agro. J. 62: 818-821.
2. BARKER, A. V., D. N. MAYNARD and H. A. MILLS. 1974. Variations in nitrate accumulation among spinach cultivars. J. Amer. Soc. Hort. Sci. 99: 132-134.
3. BINGHAM, F.T., H.D. CHAPMAN, and A.L. PUGH. 1954. Solution-culture studies of nitrite toxicity to plants. Soil Sci. Soc. Amer. Proc. 18: 305-308.
4. CANTLIFFE, B. J., and S. C. PHATAK. 1974. Nitrate accumulation in greenhouse vegetable crops. Can. J. Plant Sci. 54: 783-788.