Quality, yield and nitrogen fixation of faba bean seeds as affected by sulphur fertilization

Faba bean (Vicia faba L.) is an important source of plant protein for humans and animals; however, nutritional value of seeds is notoriously deficient in sulphur (S)-containing amino acids. In this article, the effect of S fertilization on faba bean's capability of N-2 fixation, grain yield and chemical characteristics in terms of protein fractions, fatty acids and minerals composition is reported. A randomized, complete block design with three replicates was used, and three S applications (0, 30 and 60 kg ha(-1), respectively) for faba bean were performed. The S fertilization was split into two applications: 50% before sowing and 50% in the beginning of March as K2SO4. At the same time, both the legume and oat crops were fertilized uniformly with 10 kg N ha(-1) as N-15 NH4 (NO3)-N-15 (10% N-15 atomic excess) in solution form. In a Mediterranean climate under optimal spring rainfall situations, faba bean produced high yield of grain and protein. Sulphur application resulted in an increase in overall plant yield and N-2 fixation. In addition, S fertilization enhanced the protein quality, increasing its degradable fraction. Fertilizing faba bean with 30 kg ha(-1) of S resulted in a more appropriate dose in order to obtain a quantitative and qualitative crop improvement. From our findings, it can be concluded that S fertilization to faba bean should be recommended to soils with suboptimal S levels to obtain maximum seed and protein yields.