Effects of S, N and P on amino acid composition of field beans (Vicia faba) and responses of the biological value of the seed protein to S-amino acid content

In pot experiments dry matter yield of seed of Vicia faba was increased by increasing application of S at all N- and P-levels and, by P at all S- and N-levels. Significant interactions were found for PxN (0.1%) and SxP (1%). N-concentrations generally increased with S-additions, but decreased with large applications of N and P. Significant interactions were found for PxN fl-1%) and SxP (5%) with regard to N concentration. Maximum increases in cystine and methionine contents from S-application were respectively 39.1 and 13.7% expressed as % of dry matter and 37.9 and 12.3% expressed as g/16 g N. Highly significant correlation coefficients were obtained between concentrations (g/16 gN) ofa number of protein am/no acids in seeds and total-N content. In a feeding trial with rats, the biological value of non-S treated seed was 40.8 and increased to about 60 in seed from S-treatments Addition of synthetic cystine and methionine to seed from the non-S treatment could not entirely substitute these acids present in the protein of seed from S-treatments with regard to effects on the biological value of seed protein.