The productivity of oats and berseem clover intercrops. I. Primary growth characteristics and forage quality at four densities of oats

Berseem clover (Trifolium alexandrinum L.) was sown as an intercrop with oats (Avena sativa L.) at 0, 30, 60, 90 and 240 oats plants m(-2) in May in 1999 and 2000 in Alberta, Canada. Forage yield and quality were measured at 10-d intervals between 35 and 88 d after planting (DAP). Yield is defined as the biomass above 6 cm of the soil surface. The dry-matter (DM) yield of berseem clover in sole crops increased by 5-10 g m(-2) d(-1) between 35 and 55 DAP and then increased by 21-28 g m(-2) d(-1) between 55 and 75 DAP. The DM yields of oats sown at 240 plants m(-2) increased by 26-28 g m(-2) d(-1) over the whole period from 35 to 75 DAP. Oats were the dominant component in the intercrops, even at low densities of oats. Berseem clover grown with 60 oats plants m(-2) received only 0.24 of the incident light when shading by oats peaked at 65 DAP. DM yields of berseem clover in intercrops with 60 oats plants m(-2) averaged 0.14-0.32 of the yields of berseem clover sole crops. Between 35 and 88 DAP in 2000, the crude protein (CP) concentration of berseem clover sole crops declined linearly from 310 to 180 g kg(-1) DM, and the CP concentration of oats exhibited a quadratic response, declining from 350 g kg(-1) DM at tillering to 110 g kg(-1) DM at the soft dough stage. The mean CP concentration of berseem clover in intercrops with 60 oats plants m(-2) was 25 g kg(-1) less than in berseem clover sole crops, indicating that competition by oats reduced the CP concentration of berseem clover. At later sampling dates, CP and DM yields of intercrops with oats at 60 plants m(-2) equalled those with oats at 240 plants m(-2). The addition of berseem clover to oats in intercrops at 60 oats plants m(-2) reduced the neutral-detergent fibre concentration by 30 g kg(-1) DM compared with oats alone. Oats were very competitive as a companion crop for berseem clover. Adding berseem clover to oats increased forage quality and may provide for increased intake and digestibility of forage to support higher livestock productivity.