The change in LER between 2001 and 2002 was due to Brussels sprout and tomato yields in pure stands falling more than in mixed plantings, and basil yields in mixtures increasing more than in pure stands.
Figure 7. Relative yield of primary and secondary crops in mixtures (RY_A and RY_B, respectively) as a proportion of pure stand yields in 2001 (○, n = 3) and 2002 (●, n = 4). The sum of RYs for a mixture is the land equivalence ratio (LER). Arrows show change in LER for each treatment between years. Bars denote standard errors of each mean.
Table 3. Land Equivalence Ratio (LER) of three mixtures by year ($\bar{x} \pm S.E.).
| LER |
| Mixture | 2001 (n=3) | 2002 (n=4) |
|---|
| S&B | 0.93 ± 0.13 | 1.46 ± 0.03* |
|---|
| T&B | 0.91 ± 0.07 | 1.28 ± 0.05* |
|---|
| T&S | 0.92 ± 0.10 | 1.25 ± 0.13 |
|---|
This study evaluated the effect of mixed planting in the context of BIA garden systems grown according to the methods of Jeavons (2006). Most studies that calculate LER values use either an additive design, in which the density of the primary crop is held constant between mixed plantings and pure stands, or a replacement design, in which total plant density is held constant (Freckleton and Watkinson 2000, Jolliffe 2000). The former confounds polyculture and total plant density effects; the latter