Above- and below-ground interspecific interaction in intercropped maize and potato: A field study using the 'target' technique

The association of maize (Zen mays L.) and potatoes (Solanum tuberosum L.) is an overyielding multi-cropping system. However, knowledge on specific interactions in field conditions, especially below-ground interactions, is deficient. To evaluate the nature and strength of interspecific interactions between maize and potatoes, field and pot experiments were conducted using the 'target' technique, with three interaction models: no interaction (NI), below-ground interaction (BI) and full (both above and below-ground) interaction (FI). Plants were sampled at flowering and harvest periods to measure biomass and calculate the log response ratio (lnRR), root:shoot ratio and land equivalent ratio (LER). In the field experiment, the lnRR value of both BI and FI treatments for potatoes was >0, whereas for maize it was <0. This result accorded with differences in biomass, yield, Harvest Index and root:shoot ratio between the two treatments for both crops. Results showed that maize was subjected to competition (negative interaction), while potatoes obtained facilitation (positive interaction) when they were intercropped. In addition, after flowering there were no significant differences between BI and FI treatments in terms of biomass, lnRR, yield and LER for the two crops. Thus, compared with above-ground interaction, below-ground interaction (i.e. root competition for maize and root facilitation for potatoes) plays a more important role for crop growth and intercropping advantages. In the pot experiment, however, the lnRR values of both BI and FI treatments were <0 for both crops, so potatoes did not obtain a net profit from maize. However, the competitive capability of potatoes were significantly greater than maize when they were intercropped, which is consistent with results from the field experiment. Similarly, there were no significant differences between BI and FI treatments in terms of biomass, lnRR, root:shoot ratio and LER for the two crops. In summary, our study suggests that the root facilitation produced by maize for potatoes is a mechanism for overyielding in the maize-potato intercropping system. The potential of this system merits further research. (C) 2012 Elsevier B.V. All rights reserved.