The frequency of spring harvest and row distance affect the seed and forage production of alfalfa (Medicago sativa L.) under irrigated Mediterranean conditions

Aim of study: The effect of the number of spring harvests (1 or 2) for forage before letting alfalfa (Medicago sativa L.) grow for seed, combined with three different row distances, on seed production was evaluated over a three-year period. Area of study: Irrigated Mediterranean environment (NE Spain). Material and methods: Seed yield, forage production and seed weight were evaluated, as well as final plant stands and the economic implications of different decisions. Main results: The study revealed significant differences (p < 0.01) in seed yield between the number of forage harvests prior to letting the crop grow for seed in two of the three years of the study, with an overall average of 500 kg ha-1 for one spring harvest and 450 kg ha-1 for two spring harvests, but with significant differences associated with row distance in two of the three years. The average annual production of forage was 8.08 Mg of dry matter (DM) ha-1 for the case of two spring harvests and 7.57 Mg for one, with significant differences in one of the three years. Row distances of 20, 40 and 60 cm did not significantly affect forage DM production although, on average, higher forage yields were achieved with narrow row distances. From an economic point of view, our results suggest that the 1-harvest treatment before letting alfalfa grow for seed is slightly more profitable than the 2-harvest treatment (higher gross margin of about 54.5 € ha-1). Research highlights: Under irrigated Mediterranean conditions, alfalfa harvested only once in spring before letting the crop grow for seed production maximizes the gross margin.