ABSTRACT This study presents an account of maize (Zea mays L. cv. Tundra) yield quality parameters as influenced by the foliar application of an industrial byproduct (beet vinasse). Beet vinasse is a byproduct of great agricultural interest, because of its organic matter content, and N and K concentrations. The main objective of this work was to study the effects of foliar fertilization with beet vinasse at 1000, 1500 and 2000 1 ha−1 of beet vinasse mixed with 500 1 of water in 2001, 2002 and 2003 on maize (Zea mays L. cv. Tundra) nutrition, yield and quality near Sevilla (Andalusia, Spain). Macro- and micronutrients, chlorophylls, total carotenoids and soluble carbohydrate concentrations on maize leaf samples were analysed for each experimental season at two growth stages. Also, grain mineral composition, number of grains per corncob, protein concentration in the grain, and crop yield were determined to observe the influence of the foliar fertilization with byproduct on crop quality and yield. The results show that foliar fertilization with a byproduct rich in fulvic acids, but also containing macro- and micronutrients, increased the leaf concentration of micronutrients Fe, Mn, Cu and Zn, and macronutrients N and K uptake by plants. Highest values of chlorophyll A and B were found in the foliar fertilized plots, which presumably promoted photosynthesis. Foliar application of the byproduct resulted in a significant increase in grain protein of about 30% compared with plots without foliar fertilizer, a significant increase in number of grains per corncob of about 20% compared with plots without foliar fertilizer, and a significant increase in maize yield of about 13% compared with plots without foliar fertilizer.