Mechanical management of weeds - Ecological Management of Agricultural Weeds - page 165

Figure 4.8 The changing microtopography ofa ridge-tilled field.After harvest,the
ridges are intact (a).At planting,crop residues and soil at the tops ofridges are
thrown into the inter-rows (b).At the final cultivation,soil and decomposed
residue are hilled back onto the ridges (c).(Redrawn from Forcella & Lindstrom,
1988 a .)
tances from the crop row in ridge tilled and conventionally plowed maize
plots. Before planting, seed density in the surface 7.6 cm was higher in ridge
till,especially in the crop row.After planting,seed density in the crop row was
lower and seed density in the inter-row area was higher in ridge till than in
conventional tillage (Figure 4.9).Similarly,Forcella & Lindstrom (1988 a ) dem-
onstrated that large numbers of seeds were moved away from the crop during
planting.However,despite the many individuals that germinated in the inter-
row and were killed during cultivation, the ridging operation also returned
many seeds back to the ridge. Germination after the last cultivation led to
weed populations that, though not competitive with the crop, were sufficient
to maintain the seed bank. Sensitivity analysis of a ridge tillage weed popula-
tion model indicated that movement of a large percentage of seeds from the