brassicas should not be grown together due to mutual antagonism. The fact that Brussels sprout thrives in cooler conditions than tomato or basil is a better reason for choosing not to mix these crops.
Mixed plantings used land more efficiently than pure stands in BIA systems grown according to popular recommendations in 2002. No mixture advantage was observed in 2001. Water was a more limiting resource, and RCI was lower, for all crops in 2002. Results suggest that mixed planting can increase land-use efficiency of BIA systems under resource-limiting conditions.
Popular recommendations for calculating inter-plant spacing in mixed BIA beds tend to result in lower density in mixed plantings than in segregated pure stands with the same total number of plants. This difference is more pronounced as recommended spacings for component crops diverge. Current popular recommendations do not account for the proportion of each crop in a mixed planting. New recommendations are proposed to address these problems. A spreadsheet is available for download that calculates inter-plant spacing in mixed plantings according to the revised recommendations (Bomford 2007). The new recommendations are expected to improve land-use efficiency of mixed stands and allow a fairer comparison of mixed plantings and pure stands in BIA systems.
All mixtures consisted of one crop that faced more competition in the mixture than in pure stands (RCI > 0), and another that faced less (RCI < 0). Basil was the least competitive component crop, accounting for less than one-third of LER in mixed plantings, and the only crop for which relative leaf chlorophyll content was correlated with biomass production. Brussels sprout was the most competitive crop, accounting for at least two-thirds of LER.
Two mixtures popularly recommended for BIA systems (tomato and basil; Brussels sprout and basil) did not offer superior land-use efficiency to a popularly discouraged combination (tomato and Brussels sprout). The consistently poor marketable Brussels sprout yield in all treatments was probably due to excessive heat for the cool-season crop; it was not due to poor plant growth. Cool-season crops should not be mixed with warm-season crops for synchronous growth in mixed plantings.
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Barret, C.B. 1993. On price risk and the inverse farm size–productivity relationship. University of Wisconsin–Madison, Department of Agricultural Economics Staff Paper Series no. 369.