Influence of sulphur application on protein quality, fatty acid composition and nitrogen fixation of white lupin (Lupinus albus L.)

White lupin (Lupinus albus L.) is an important source of plant protein for both humans and livestock, due to high protein content, low alkaloids level, high level of unsaturated fatty acids, price and market availability in many countries. In this paper is reported the effect of S fertilization on white N fixation capability of lupin, grain yield and chemical characteristics in terms of protein fractions, fatty acid and mineral composition. Randomized complete block design with three replicates was used, and three S applications (0, 30 and 60 kg ha-1, respectively) for white lupin were used. The S fertilization was split into two: 50 % before sowing and 50 % in the early of March as K2SO4. At the same time, both the legume and oat crops were fertilized uniformly with solution of 10 kg N ha-1 15N NH4 15NO3 (10 % 15N atomic excess). Data indicated that under Mediterranean environment on sub-alkaline soil, white lupin produces low grain and protein; however, S application increased plant yield and N fixation. In conclusion, it seems that S fertilization to white lupin should be recommended to soils with sub-optimal S levels to obtain maximum seed and protein yields. Moreover, S fertilization enhanced the protein quality increasing its degradable fraction, and improved the lupin oil quality through the increase in oleic and linolenic acids and the remarkable decrease in erucic acid.