Mediterranean Lupines as an Alternative Protein Source to Soybean ^†

Soybean is the most commonly used protein supplement of plant origin in animal diets. However, its high price and environmental impacts of production and transport to global markets stimulate producer’s interest in alternative use of locally produced feed ingredients including grain legumes. Lupin is one of the major grain legumes economically cultivated in Europe. Their seeds are characterized by high protein and dietary fiber content, presenting a high nutritional value for animal feeding. There is the need for screening new alternatives that can replace soybean by traditional protein sources with nutritional and commercial value for human and animal consumption. The aim of this study was to evaluate the effects of sowing date on the potential of 3 lupines varieties well adapted to Mediterranean climatic conditions and soils from North Portugal as an alternative protein source to human and animal feed. The species and varieties tested were white lupine (Lupinus albus L.), cv. Estoril, narrow-leafed lupine (Lupinus angustifolius L.), cv. Tango, and yellow lupine (Lupinus luteus L.), cv. Cardiga. Four sowing dates with 3-weeks interval were tested from early September to November. The sowing was performed manually in a split-plot completed randomized block design with plots of 10m² each and 4 replications. The harvest was carried out during the month of June. Agronomic parameters like plant growth indicators, weed infestation, grain yield and protein content were evaluated. Data were analyzed by analysis of variance (ANOVA), using the Statistix 10 (Analytical Software 10). When the effects of the factors or their interactions were significant (p < 0.05), the means were separated using multiple comparisons of the Tukey test. Early sowing of Estoril yield more grain than Cardiga (1766 and 1552 kg ha⁻¹, respectively). Late sowing dates significantly reduced (59–62%) yields compared to early sowing. In contrast, Tango showed always the lowest grain yield in all sowing dates with a reduction of 91% and the highest weed infestation on the last date compared to the first one. The highest crude protein yield was obtained with Cardiga (618 kg ha⁻¹) and Estoril (588 kg ha⁻¹), while the lowest was in Tango (144 kg ha⁻¹). The grain protein content decreased from first to last sowing date, with a reduction to half in Estoril and Tango and Cardiga showing 59% less, in last sowing. In conclusion, Cardiga followed by Estoril showed more adaptability to the region and may constitute an alternative protein source for the feed industry.