Mechanisms of weed suppression by squash (Cucurbita spp.) intercropped in corn (Zea mays L.).

摘要

Ecologically based methods of weed management are needed to reduce the environmental harm caused by herbicides and cultivation. The traditional practice of interplanting squash into corn provides agroecologists with a source of ideas from which to develop techniques for weed management in diverse systems.; This dissertation shows the ability of interplanted squash to suppress weeds in a region different from where it is normally interplanted and examines the hypotheses that light competition and allelopathy are responsible for the suppression. Trials of interplanted squash density demonstrated squash's ability to suppress temperate zone weeds, notably the dominant species of the system as well as a rhizomed perennial species that resists mechanical cultivation. Low-density squash reduced weed biomass with no loss of corn yield under conditions of plentiful moisture, while higher densities were detrimental to both weeds and corn, as was a gap in irrigation.; A field experiment compared the level of weed suppression from the shade of an artificial canopy with the suppression due to the whole squash plant. Light interception was initially higher in the corn-squash intercrop, but it was surpassed by the corn monocrop with the artificial canopy. Weed biomass was correlated with light levels across all treatments, but the data suggest an additional factor, such as allelopathy, contributes to weed suppression.; Laboratory and greenhouse experiments using compounds that would normally be released from squash plants under natural conditions showed that nonpolar exudates from living roots had allelopathic activity, inhibiting target plant growth. Senesced leaves were inhibitory at the high concentrations tested, while leaf glandular trichome volatiles showed some stimulatory activity toward the target species. Fog drip had no allelopathic activity.; Guidelines for weed management using squash interplanted in corn include avoiding too high a density of squash and providing plentiful moisture. Recommendations for future study include a more thorough light-monitoring regime for comparing an artificial canopy with a natural one, studying the interactions of corn and squash varieties with a history of interplanting versus those normally monocropped, and identification of squash allelochernicals and their testing on weed species in soil.