The effect of row spacing on alfalfa seed and forage production under irrigated mediterranean agricultural conditions

We evaluated the effect of row spacing on seed and forage yields in alfalfa (Medicago sativa L.) using combined seed and forage production plots, in an irrigated Mediterranean agricultural environment. We compared three row distances (20, 40 and 60 cm) in two cultivars at a seed rate of 25 kg ha−1 over a period of 4 years. We measured the seed yield and yield components as well as forage production. The 4-year average revealed an overall clean seed yield of 367 kg ha−1 declining over time, without significant differences in row distances. The number of shoots per square metre differed significantly as a function of row spacing, with averages of 357, 226 and 172 shoots m−2 for row widths of 20, 40 and 60 cm respectively. The row spacing did not affect the number of racemes per shoot (23·1), the number of pods per raceme (7·2), the number of seeds per pod (6·5) or the thousand seed weight (1·667 g). The average forage production was 20·1, 18·5 and 17·9 Mg DM ha−1 for row distances of 20, 40 and 60 cm, respectively, with higher yields associated with smaller row distances. Our data demonstrate that row spacing >20 cm does not confer any advantage to the production of alfalfa seed under irrigated Mediterranean agricultural conditions and that close spacing can significantly increase forage yields in the same environment