Agriculture Reference
In-Depth Information
Crop rotation is also essential for regulation of weeds in cereal crops. Summer cereals should
be preferentially grown when winter weeds, such as mouse foxtail (
Alopecurus myosuroides
Huds.), scentless mayweed (
Matricaria maritima
L.), catch weed (
Galium aparine
L.), hair grass
(
Apera spica - venti
L.), field poppy (
Papaver rhoeas
L.) are problematic, while winter crops can
better be grown when summer weeds (such as wild oats or wild rape seed) occur more
frequently. Cereal crops show different competitive strengths against weeds. In general, winter
cereals are more competitive than summer cereals, rye more than wheat, and oat more than
summer barley. In the low-stem cereals under sown cover crops (from genus
Trifolium
) can be
included, because they compete generally well with weeds after harvest and represents the
further leguminous in the crop rotation.
Crop rotation also contributes to the regulation of pests and diseases. Black stalk or take-all
disease (
Gaeumannomyces graminis)
and eyespot disease (
Pseudocercosporella herpotrichoides
)
represent major fungal diseases of cereal crops that are strongly affected by rotation. Take-all
is commonly suppressed by antibiotic-producing
Pseudomonas fluorescens
bacteria when wheat
is grown without rotation [12], but this is not an option for organic wheat production. In
organic farming systems, take-all can be reduced by using soil-improving, non-susceptible
annual crops in the rotation, because the pathogens do not persist in soil for a long time period.
Suitable
G. graminis
-interrupting crops are maize, oat, potatoes, sugar beet, legumes, rape, or
flax. High microbial activity and diversity, promoted by a complex rotation, also contribute to
take-all control [12]. Cereal crops need to be interrupted by other crops for at least 2-3 years to
limit eyespot occurrence. The most suitable crops for this purpose are clover or alfalfa for 2 -
3 years. Very suitable are sequences of these crops, for example maize - oat, potatoes - oat,
potatoes - legumes etc. However, to prevent the build-up of smut diseases, such as
Tilletia
controversy
on wheat and
Ustilago maydis
on maize, longer rotations of 6-8 years are re‐
quired.This is especially true when organically produced seeds are used, as the common seed
treatments are not allowed. Too many cereal crops in the rotation may also enhance the risk
of foliar diseases such as powdery mildew (
Erysiphe graminis
). Due to low resistance of cereals
to the diseases, one of the most effective measures for stable yielding is intercropping of
different species of cereals [13] or just different varieties (with the same harvesting time) of
one cereal species [14].
The most frequent cereal pests are aphides, damaging the assimilatory organs and spikes. As
cereal aphids are quite specific, it is important to rotate with non-cereal crops. In Europe and
Western Asia, the corn ground beetle (
Zabrus gibbus
) can be very damaging, especially on
wheat [15]. The most damaging pests in maize are corn borer (
Ostrinia nubilalis
L.) and Western
corn rootworm (
Diabrotica virgifera
L.), becoming new pests in Eastern Europe. Rotation of
cereals with legumes and beet is a sufficient measure against these pests, which' larvae damage
green grains and adults feed on crop flowers and grains during milk ripe stages. Wire worms
(larvae of the click beetle) can be a major pest in organic crop production, especially after
incorporation of large amounts of crop residues, for example perennial fodder crops or a cereal
crop with under sown grass-clover. Populations of click beetles are generally reduced by
cultivation operations. As root crops and rape seed require multiple cultivation operations,
these crops are more suitable for rotation.
