Weeds and the soil environment - Ecological Management of Agricultural Weeds - page 246

Figure 5.10 Effects ofcrimson clover residue and ammonium nitrate fertilizer on
aboveground biomass production of Chenopodium album (a) and sweet corn (b)
grown in pure stands in a field experiment conducted in Maine,USA.0 and 60
indicate fertilizer rates in kg N ha 1 .(After Dyck & Liebman,1994.)
by clover residue,but increased by N fertilizer (Figure 5.10a).At the end of the
experiment, 53 days after planting, C. album biomass was 64% lower in the
treatment receiving clover residue but no fertilizer compared with the treat-
ment receiving 60 kg N ha 1 of synthetic fertilizer but no clover residue. In
contrast,sweet corn biomass production was unaffected by clover residue or N
fertilizer (Figure 5.10b), perhaps because of high background soil fertility or
too short a growth period. Incorporation of clover residue had no significant
effects on soil moisture and temperature, and no disease symptoms were
observed (Dyck & Liebman, 1994).
Chenopodium album and sweet corn also were grown in competition at fixed
densities in a two-year field experiment (Dyck, Liebman & Erich, 1995).
Biomass of the weed species was 39% lower, on average, in a treatment receiv-
ing crimson clover green manure, but no synthetic fertilizer, than in a treat-
ment receiving 45 kg N ha 1 as ammonium nitrate, but no clover residue. In
contrast, when grown in competition with C. album , sweet corn biomass was
20% higher in the clover treatment than the synthetic fertilizer treatment.
Comparison of sweet corn biomass from plots with and without C.album indi-