Diversifying crop rotations with temporary grasslands - Université de ...

Clay & Aguilar (1998) compared the weed seed banks, weed biomass and corn yields after (i)
continuous corn or (ii) corn grown after 2-year-alfalfa stands with three fertilizer and
herbicide input levels in South Dakota, USA. Alfalfa had positive impacts on corn yields and
weed control, especially for the low and intermediate input systems.
Schoofs & Entz (2000) compared the weed suppressive potential of five different spring
seeded one-year forage crops followed by a pea (Pisium sativum L.) test crop. All forage
systems were at least as effective as a sprayed wheat (Triticum aestivum L.) control in
suppressing Avena fatua L. and sometimes Setaria viridis L. Beauv. grass weeds; however,
effects on broadleaved weeds were variable, especially for systems that did not provide
season-long competition. In general, one-year forage crops showed significant weed control
benefits, but benefits of pluriannual forage crops reported by the same research team (Entz et
al., 1995) were stronger. The effectiveness of the different grain and forage crops to reduce
weed seed production ranked as following: fall rye (Secale cereale L.) (grain crop) > winter
triticale (Triticosecale) (simulated grazing) > spring/winter triticale intercrop (silage, then
simulated grazing) > sorghum-sudangrass (Sorghum bicolour [L.] Moench × Sorghum
sudanese [Piper]) (hay) = alfalfa (hay) > spring triticale (silage) = weed fallow (silage) =
sweet clover (Melilotus officinalis L.)/winter triticale double crop (hay, then simulated
grazing) > wheat grain crops with three different herbicide regimes.
Sjursen (2001) monitored the development of weed densities in the seed bank and the emerged
vegetation in organic 6-year rotations including 3-year periods of perennial grass-clover leys
and a sequence of three annual crops. Seed densities of dicotyledonous weed species were
highest after the 3 annual crops (about 17600 seeds m -2 ) and lowest after the ley periods (7200
seeds m -2
), indicating a reduced seed input during the ley periods. In the emerged vegetation,
species richness decreased from 19-20 during the annual crops to 8 in the third year ley crop
while it remained constant in the seed bank (18-21 species). However, correlations between
seed bank and emerged weed densities were rarely significant limiting the potential for
predicting the actual weed vegetation.
Cardina et al. (2002a) and Sosnoskie et al. (2006) compared the weed seed density, diversity,
and community composition between three crop rotations: continuous corn (CCC), cornsoybean
(CS), corn-oat-hay (COH) and three tillage systems (conventional, minimum, and no-
tillage) that were applied in two 35-year field experiments in Ohio, USA. Crop rotation was a
more important determinant of weed seed density and species composition than tillage system.
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