Plant Population Density Effects on Seed Yield of Birdsfoot Trefoil1

Abstract

AbstractLittle is known about the effects of plant population density (PPD) on birdsfoot trefoil (Lotus corniculatusL.) seed production. Our objective was to ascertain the effects of a wide range of PPDs on seed yield and yield components of birdsfoot trefoil. ‘Norcen’ and ‘Viking’ birdsfoot trefoil were transplanted into the field at Roseau and St. Paul, MN in 1981 and 1982, respectively. An experimental design was used which provided 19 PPDs from 1.6 to 61 plants/m2. The Roseau soil was a Glyndon silt loam (coarse‐silty, frigid Aeric Calciaquoll) and the Rosemount soil was a Waukegan silt loam (Typic Hapludoll). Plants were sampled individually when the majority of their pods were brown. Forage yield, seed yield, seed yield components, and harvest index were measured on each plant. Seed yield/m2and forage yield/m2had asymptotic diminishing‐returns relationships to PPD. Forage yield/m2increased about 200% as PPD increased from 1.6 to 61 plants/m2. The PPD at which forage yield/m2reached 90% of its total change was 26.5 plants/m2. Seed yield/m2increased about 75% as PPD increased from 1.6 to 61 plants/m2. The PPD at which seed yield/m2reached 90% of its total change was 19.0 plants/m2. Seed yields were adjusted in response to increasing PPD by reductions in all yield components. Umbels per plant was most responsive to PPD, pods per umbel and seeds per pod had intermediate sensitivity to PPD, and seed mass showed the least change in response to PPD. Harvest index decreased as PPD increased, indicating that seed yield/m2increases were smaller than forage yield/m2increases as PPD increased. Plant population densities required for optimum seed production are less than those required for optimum forage production; thus, lower seeding rates may be used in establishing seed production fields.