STUDIES ON THE CEREAL ECOSYSTEM
115
Only 16% of cereals are grown on mixed farms, a further 8% on farms
with extensive grazing (sheep and cattle) and 16% on intensively
grazed (dairy) farms. Of course, the simplified and larger farms mean
more of the same kind of crops in the same vicinity.
D . T H E F L O R A O F C E R E A L F I E L D S
The overall impression for most of the spring and summer is that
modern cereal fields are clean monocultures and that most variation is
clearly “between fields” rather than “within fields”. A total of 260
fields were examined in detail twice in June in both 1970 and 1971.
To summarize, 30% of the fields contained “very few” dicotyledonous
weeds; SOYo were classed as intermediate, generally “clean with odd
patches of weeds” or, sometimes, with only one main species of weed;
whilst 20% contained a dense and varied flora. Even here, however, the
post-spraying weed populations were usually insufficient to affect
yields by direct interspecific competition with the crop.
The dominant weeds in the cereal fields in mid June 1972 are given
in Table 111. Chickweed, the speedwells and Polygonum spp. are the
most important. Some species, which were always scarce but were
nevertheless widespread, do not appear in the list; for example, the
mouse-eared chickweed (Cerastium vulgatum L.), ribwort and other
plantains (Plantago spp.) and toadflax (Linaria vulgaris Mill.). Also
under-represented are the small sessile species such as Stellaria pallida
(Durn.) PirB, Arenaria leptoclados (Rchb.) Guss. and dwarf spurge
(Euphrbia exigua L.). Other weeds, such as the corn spurrey (Spergula
arvensis L.) and corn gromwell (Lithspermum arvense L.), are not
included since they were extremely local. After harvest, conventional
quadrats are easy to place; the frequency distribution of weed species
on the stubbles was given and discussed in an earlier paper (Potts,
19704.
There is very little evidence about long-term changes in weed
populations, but Fryer and Chancellor (1971) noted that although 20
years of near continuous spraying in cereal fields had reduced the overall
abundance of broad-leaved weeds, the total number of species present
showed no signs of having decreased. Grass weeds have, however,
increased in abundance; Avena spp. (wild oats) have spread widely in
the U.K. and blackgrass (Alopecurus myosuroides Huds.) is becoming
more troublesome.
Since the introduction of MCPA and 2, 4-D in 1946, there has been a
great increase in the use of chemicals for weed control in cereal crops
in Britain (Woodford, 1964). Whilst the use of herbicides has resulted
in the decrease of weeds such as Sinapis arvensis L., Papaver rheas L.
115
Only 16% of cereals are grown on mixed farms, a further 8% on farms
with extensive grazing (sheep and cattle) and 16% on intensively
grazed (dairy) farms. Of course, the simplified and larger farms mean
more of the same kind of crops in the same vicinity.
D . T H E F L O R A O F C E R E A L F I E L D S
The overall impression for most of the spring and summer is that
modern cereal fields are clean monocultures and that most variation is
clearly “between fields” rather than “within fields”. A total of 260
fields were examined in detail twice in June in both 1970 and 1971.
To summarize, 30% of the fields contained “very few” dicotyledonous
weeds; SOYo were classed as intermediate, generally “clean with odd
patches of weeds” or, sometimes, with only one main species of weed;
whilst 20% contained a dense and varied flora. Even here, however, the
post-spraying weed populations were usually insufficient to affect
yields by direct interspecific competition with the crop.
The dominant weeds in the cereal fields in mid June 1972 are given
in Table 111. Chickweed, the speedwells and Polygonum spp. are the
most important. Some species, which were always scarce but were
nevertheless widespread, do not appear in the list; for example, the
mouse-eared chickweed (Cerastium vulgatum L.), ribwort and other
plantains (Plantago spp.) and toadflax (Linaria vulgaris Mill.). Also
under-represented are the small sessile species such as Stellaria pallida
(Durn.) PirB, Arenaria leptoclados (Rchb.) Guss. and dwarf spurge
(Euphrbia exigua L.). Other weeds, such as the corn spurrey (Spergula
arvensis L.) and corn gromwell (Lithspermum arvense L.), are not
included since they were extremely local. After harvest, conventional
quadrats are easy to place; the frequency distribution of weed species
on the stubbles was given and discussed in an earlier paper (Potts,
19704.
There is very little evidence about long-term changes in weed
populations, but Fryer and Chancellor (1971) noted that although 20
years of near continuous spraying in cereal fields had reduced the overall
abundance of broad-leaved weeds, the total number of species present
showed no signs of having decreased. Grass weeds have, however,
increased in abundance; Avena spp. (wild oats) have spread widely in
the U.K. and blackgrass (Alopecurus myosuroides Huds.) is becoming
more troublesome.
Since the introduction of MCPA and 2, 4-D in 1946, there has been a
great increase in the use of chemicals for weed control in cereal crops
in Britain (Woodford, 1964). Whilst the use of herbicides has resulted
in the decrease of weeds such as Sinapis arvensis L., Papaver rheas L.