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Root distribution by depth in five different systems: monocultures of maize (MMM), bean (BBB) and squash (SSS) and polycultures of maize and bean (MBB) and maize, bean and squash (MBS). Panels show root distribution of nitrate stressed or non-stressed plants at a soil-nitrate availability of 15·6 (A) and 156 kg ha−1 (B). For explanation of availability see Fig. 2.
