Effect of sulfur fertilization and variety on yield and contents of crude protein and amino acids of organically produced blue lupins (Lupinus angustifolius L.)

Summary

Grain legumes, like blue lupins, are important protein feedstuffs especially in organic farming. Their content of crude protein (CP) and essential amino acids (EAA) is of great interest. The sulfur-containing amino acids (SAA) methionine and cysteine are often limiting in common diets primarily for poultry. Therefore, we investigated, whether a sulfur fertilization of blue lupins could enhance their contents of SAA and if it has other effects regarding crop yield, CP and further EAA.
Two branched (Boregine, Probor) and two determinated (Boruta, Sonet) blue lupin varieties were cultivated at an experimental station in Northern Germany in the years 2012, 2013, and 2015. The varieties were either grown with or without S fertilization (40 kg S ha-1; MgSO4). Samples were analyzed for CP and amino acids (AA) with NIRS. Statistical analyses were done with SAS 9.4 (proc glm).
The yield and the contents of CP and AA differed depending on variety in the observed years. Boregine showed the highest yield and Probor the highest CP content. Boruta had the lowest yield and CP content. Sulfur fertilization was able to increase the amount of SAA in some varieties but tended to decrease lysine and threonine content without affecting crop yield or CP content. This might be due to an altered storage protein ratio. Hence, sulfur fertilization could be beneficial by increasing SAA in blue lupin varieties. Further investigations on the effect of sulfur fertilization for other legumes are requested.