Mechanical management of weeds - Ecological Management of Agricultural Weeds - page 166

Figure 4.9 Density ofseeds at three distances from the crop row after planting in
ridge tillage and conventional tillage.(Drawn from data in Wicks & Somerhalder,
1971.)
ridge to the furrow is critical in limiting seed bank and weed density (Jordan,
1993).Accordingly, Buhler (1998) observed that deep scraping of the ridges at
planting reduced seedling densities of several species relative to shallow
scraping.
In Forcella & Lindstrom's (1988 a , 1988 b ) study, overall weed seed density
was similar in ridge and conventionally tilled treatments that were rotated
between maize and soybean, but in continuous maize, seed densities were
higher with ridge till. The difference may have been due to greater soil crack-
ing in continuous maize, allowing seeds to fall below the depth to which the
ridge was scraped at planting. The higher seed density resulted in greater
seedling density in ridge till in one of two years.These results show how inter-
actions among agronomic practices can affect weed management.
Comparison of ridge tillage plus rotary hoeing with conventional tillage
plus herbicides in 51 on-farm trials in Iowa showed no yield difference, only
slightly higher average weed densities,and substantial cost savings with ridge
tillage (Exner, Thompson & Thompson, 1996). The long experience of many
farmers with this tillage/weed management system has resulted in several rec-
ommendations (Thompson & Thompson,1984; Cramer et al .,1991,pp.25-9).