Weeds and the soil environment - Ecological Management of Agricultural Weeds - page 211

Thus a major task for the development of ecological weed management is to
identify soil management strategies that predictably reduce weed growth and
reproduction, while enhancing crop performance. Although this work is just
beginning, sufficient data exist to suggest four general principles for manag-
ing weeds through manipulations of soil temperature, moisture, nutrient,
and residue conditions.
1. Before and after seasons of crop production, weed seeds and perennating structures
can be killed by altering soil moisture and temperature regimes. Attacking weeds
when crops are not present allows the use ofnon-selective techniques,
such as solar heating and flooding,that are potentially lethal to both
crops and weeds.Destruction ofweed propagules during “off-seasons”
reduces the density ofweeds present when crops are sown.
2. During seasons of crop production, resources can be made differentially accessible to
crops and inaccessible to weeds .Both the location and timing ofresource
availability may be regulated by management activities.Emphasis
should be placed on providing resources to the crop where and when it is
best able to use them,and on depriving weeds ofresources during criti-
cal periods ofgrowth and development.
3. When resources are accessible to both crops and weeds, differential responses
between species to soil conditions can be exploited to stress weeds and enhance crop
performance .Differences can exist between crops and weeds in their ger-
mination and growth responses to soil thermal regimes,nutrient
sources,residue amendments,and temporal patterns ofmoisture and
nutrient availability.When these differences exist,the goal ofsoil man-
agement is to create conditions that favor crops and place weeds at a dis-
advantage.Plants given an initial growth advantage over their neighbors
by manipulation ofsoil conditions can become superior competitors for
light for the remainder ofthe growing season.
4. Shifts in weed community composition occur in response to manipulation of soil
conditions. Because soil management can have strong effects on plant per-
formance,and because species are affected unequally by changes in soil
conditions,shifts in weed community composition toward tolerant taxa
are likely to occur unless multiple weed management tactics are used.
Soil management practices should be components ofmultitactic weed
management strategies that subject weeds to diverse types ofstress.
In the following sections of this chapter, we examine applications of these
principles in a wide range of agricultural ecosystems.This survey is not meant
to be a complete catalog of management practices. Rather, our intent is to
stimulate consideration of the many possibilities that soil management offers
to weed management and to suggest potentially fruitful lines of research.