Weeds and the soil environment - Ecological Management of Agricultural Weeds - page 255

erosion is less of a problem.Such systems also provide an additional option for
shifting tillage from spring to fall in regions where spring-sown row crops
predominate (see Chapter 7).
Third,crops can be planted without tillage into killed cover crops,and then
cultivated with high-residue cultivators after the crop is established. The
principal soil conservation advantage of no-tillage crop production occurs
between planting and canopy closure, since cover crops can be used to protect
soil during the preceding fallow season regardless of the tillage regime. After
a main crop is established in a cover crop mulch, its leaves and roots increas-
ingly protect the soil, and inter-row cultivation presents only a minor risk of
erosion. With regard to weed control, the principal point of mulch is to sup-
press weeds in the crop row. In many studies in which weed control by mulch
alone was considered inadequate, overall weed control would have been satis-
factory if weeds in the inter-row area had been eliminated by cultivation.
As discussed in Chapter 4, several types of implements are available that
can cultivate without jamming on dense residue, though none is ideal with
regard to soil movement and stability in hard,untilled ground (C.L.Mohler,J.
Mt.Pleasant & J.C.Frisch,unpublished data).Few studies have examined cul-
tivation in mulch systems, but Liebman et al . (1995) found that two inter-row
cultivations provided adequate weed suppression in dry bean after planting
without tillage into herbicide-killed rye provided field margins were mowed
to prevent seed production by Taraxacum officinale. Cultivation of untilled
fields covered by mulch remains a challenge and continued work on this
problem by agricultural engineers and farmers is highly desirable.
Mowing is an alternative approach to cultivation for controlling weeds
between rows in mulch systems. Although mowing generally provides only
short-term weed suppression, this may be adequate in a vigorously growing
crop,especially if weed pressure has been reduced by the mulch.Baryeh (1987)
found inter-row mowing was as effective as hoeing or hand pulling at reduc-
ing weed biomass and preserving maize yield.However,mowing significantly
speeded decomposition of the dead velvet bean mulch relative to the other
weeding methods.
Machinery can be used to address the problem of too much mulch for
optimal crop emergence and growth,as well as the converse problem of insuf-
ficient mulch for adequate weed suppression. Several types of “trash wheels”
are currently marketed to remove residue from the crop row. These decrease
problems that arise when attempting to no-till plant through heavy residue,
and allow quicker warming of the soil in spring-planted crops in cool climates
(Swan, Kaspar & Erbach, 1996). Their performance in the heavy residue from
killed cover crops needs to be explored.