The Impact of Parthenium Weed-Amended Substrates on the Germination and Early Growth of a Range of Pasture and Crop Species

Abstract

Parthenium weed (Parthenium hysterophorus L.) is an internationally important invasive weed native to the tropical and sub-tropical Americas, and invasive in more than 30 countries. This weed has serious adverse influences on rangeland and agricultural crop production, on human and animal health, and on the biodiversity of natural communities. Parthenium weed leaf litter can reduce seedling emergence and affect the early growth of a wide range of pasture and crop species. Soil collected from a heavily infested parthenium weed area was shown to reduce seedling emergence of a wide range of test plants (lettuce (Lactuca sativa L.), maize (Zea mays L.), curly windmill grass (Enteropogon acicularis L.), and liverseed grass (Urochloa panicoides P.Beauv.)) by between 20 to 40%; however, the soil had no effect on the subsequent growth of the surviving test plants. Soil amended with dried parthenium weed leaf litter reduced the emergence of test species by ca. 20 to 40%, but it had no effect on the growth of the surviving test plants. One week after emergence, the growth of all test species was stimulated by 9 to 86% in the leaf litter-amended soil with the increased growth matching the increased amounts leaf litter amended. In parthenium weed-infested landscapes, the substrate (soil) is affected by the plant during the growing season by the release of allelopathic chemicals. However, the plant’s litter can affect the community outside of the growing season, first through a residual allelopathic activity, but also by a fertilizing effect as litter breakdown occurs. This study demonstrates the significant ability of parthenium weed to affect plant communities throughout the year and, when considered over several years, this may lead to the creation of a complete monoculture of the weed.