Appropriate Ratio of Legume to Grass for Spatially Separated Pasture Systems.

Adjacent monocultures of grass and legume within the same paddock may help alleviate constraints to widespread adoption of legumes in pastures associated with reliance on binary mixtures.  Recent studies demonstrated that a 50:50 land area ratio of adjacent monoculture grass and legume had greater average daily gain (ADG) than traditional binary mixtures, but there are question regarding an optimum ratio.  A 2-yr grazing study evaluated five forage system (FS) treatments of legume-grass adjacent monocultures with one species occupying 0, 0.25, 0.5, 0.75 or 1.0 land area ratio of 0.34- or 0.67-ha experimental units. Two Angus crossbred steers (Bos taurus; initial body weight 252 ± 31 kg) were assigned to each paddock at two stocking rates (SR; 3 or 6 animal ha^‑1).   The grass component was ‘Marshall’ annual ryegrass (Lolium multiflorum Lam.) and the legume component was ‘Durana’ white clover (Trifolium repens L.).  Treatments were arranged in a 5 × 2 factorial of a completely randomized design with two replications.  Between forage species, herbage mass (HM) of grass (2.9 Mg ha^‑1) was greater than legumes (2.1 Mg ha^‑1).  Across FS, HM was not different among legume stands but grass stand HM was less at 0.75 legume ratio FS compared to other grass stands.  Weighted average HM among FS treatments decreased as legume ratio increased.  Also, at the 0 to 0.5 legume ratio FS, HM decreased as the season progressed but remain constant or increased when the legume ratio was 0.75 and 1.0.  Among treatments, ADG fluctuated from 0.62 to 0.93 kg in 2012 and 0.90 to 1.07 kg in 2013 but across years, increased with increasing legume ratio in the FS during the last month of the season when nutritive value is expected to decrease with increasing temperatures. These results suggest that pastures with a greater land area ratio of legume than grass may produce better animal performance during the late spring and early summer.  Also, even with the same season-long animal performance on pure grass stands, systems with legumes may be beneficial because of reduced N fertilizer requirements.