Mechanical management of weeds - Ecological Management of Agricultural Weeds - page 141

proportion of crop seeds that produce established plants (Carter & Barnett,
1987; Griffith et al ., 1988; Cox et al ., 1992) and improve root growth through
better aeration, reduced bulk density, and lower soil resistance to penetration
(Bauder, Randall & Swann, 1981; Cox et al ., 1990).All these effects potentially
improve crop productivity.
Moreover, although reduced tillage practices are often advisable, soil can
usually be conserved effectively without complete elimination of tillage if
other conservation practices are used.These include cover crops, soil building
crop rotations, contour plowing and planting, and sod berms and waterways.
Integrated use of such practices can improve soil properties and greatly reduce
erosion relative to conventional tillage cropping systems (Cacek, 1984;
Reganold, Elliott & Unger, 1987).Jackson (1988) compared two adjacent Ohio
farms on an erosion-prone soil.One was in no-till management; the other was
regularly tilled but had been treated with soil building rotations, cover crops,
manure, and reduced compaction practices for 70 years. The tilled farm
showed no indication of erosion and had lower bulk density and higher infil-
tration rates and soil organic matter than the no-till farm (Jackson, 1988).
Most erosion attributed to tillage results from the exposure of soil to wind
and rain that occurs when surface organic matter is buried, rather than from
soil disturbance per se . Chapter 5 addresses ways for maintaining surface
organic matter on tilled land.
Mechanical management of perennial weeds
Effects of tillage practices on established weeds
Different tillage implements move the soil in different ways and
therefore have substantially different effects on weed populations (Table 4.1).
Moldboard plows invert the soil (Nichols & Reed, 1934), and consequently
tend to bury growing weeds with relatively little dismemberment. Chisel
plows and field cultivators invert the soil to a lesser extent than moldboard
plows, but still tend to bury weeds. The primary action of a chisel plow is to
create a wake of soil rolling back from the tool. Plants in the immediate track
of the blade are likely to be uprooted, as will small weeds that are affected by
the lateral cracking of the surface soil.However, damage to well-rooted plants
more than a few centimeters from the blade is more likely to occur by burial
than by uprooting.In contrast,sweep plows and field cultivators tend to heave
up the soil vertically as it passes over the sweep, as well as throw it laterally
away from the shank. The blade severs the roots of large weeds, uproots
smaller weeds, and buries both with soil. The degree to which weeds and
residue are mixed into the soil depends on the angle of the blade relative to