Weeds and the soil environment - Ecological Management of Agricultural Weeds - page 254

involved clearly requires active cross-disciplinary collaborations among
researchers.
Mulch systems and mechanical weed management
Maintenance of large quantities of crop residue on the soil surface has
major advantages for soil conservation (Langdale et al .,1994),and as discussed
previously, can provide important opportunities for weed suppression.
Significant challenges for weed management can occur in such systems,
however, including increased prevalence of perennial weeds associated with
no-till cropping, reduced crop competitive ability due to lower soil tempera-
tures, and increased growth of weeds that do emerge through the mulch.
Probably the greatest obstacle to the use of mulch in cropping systems relying
primarily on ecological weed management methods is the lack of options for
mechanical weed control. At present, maintaining soil coverage by residue
produced in situ requires no-till cropping, but no-till systems without herbi-
cides generally have not been developed, and even research on no-till systems
with reduced herbicide reliance is still in its infancy.Several approaches might
be taken to address this challenge.
First, with proper machinery most organic material could be retained on
the soil surface during tillage, either by picking the material up with a rake
and rolling or blowing it onto freshly tilled ground, or by picking it up and
passing or blowing it over the tillage implement. For both methods, primary
and secondary tillage would need to be performed together, since the residue
would be more difficult to pick up a second time, particularly if furrows were
present. Another approach would be to develop combination undercut-
ter/chisel plows to create substantial soil disturbance below 5-10 cm, while
avoiding inversion or lateral displacement of the surface soil. The wing chisel
developed by Heilman & Valco (1988) is a first step in this direction. These
approaches allow the advantages of tillage for management of perennial
weeds, while still retaining large quantities of residue on the soil surface for
soil conservation and suppression of annual weeds.
Second, although continuous no-till cropping on a large scale is probably
impossible without herbicides, growing specific crops without tillage and
herbicides may be feasible within a rotating tillage regime. Peters, Bohlke &
Janke (1990) found that maize planted without tillage into mowed hairy vetch
had adequate weed control and was as productive as conventionally planted
maize, provided the ground was tilled before planting the vetch.Thus, even if
tillage is considered necessary for suppression of perennial weeds, the time of
tillage perhaps can be shifted from spring-planted row crops, where the
potential for soil erosion is substantial, to fall-seeded cover crops, where