Comparison of the Growth Responses of Spring and Summer Plants of Alfalfa Red Clover, and Birdsfoot Trefoil1

Alfalfa (Medicago satlva L.), medium red clover (TriFolium prateuse L.), and birdsfoot trefoil (Lotus corniculatus L.) are important forage legumes in the northern United States. The current study was conducted to directly compare the growth of summer (second‐crop) plants with that of spring (first‐crop) plants. Soil cores spring plants were removed from the field before growth started and were stored at —2 C. When plants were at full bloom in the field, soil cores of plants again were removed and shoots were cut to leave 5‐cm (short) and 12‐cm (tall) stubbles. Spring and summer plants then were grown together under identical conditions. Spring and summer alfalfa plants produced essentially the same yields of herbage. In contrast, spring plants of trefoil and red clover produced significantly more herbage than summer plants. However, summer red clover plants yielded similarly at both stubble heights, while summer trefoil herbage yields were significantly higher with a tall than with a short stubble. We conclude that the differential yield between spring and summer plants of trefoil was due to differences in carbohydrate reserves, while differential yield between spring and summer plants of red clover was due to differences in shoot initiation. The results explain in part why alfalfa is normally a higher yielding species than red clover or birdsfoot trefoil. They also reconfirm that a tall stubble is needed for trefoil to produce a satisfactory regrowth after cutting.