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

A.V DIVERSIFIED CROPPING SYSTEM CONCEPT
A diversified cropping system is proposed to alleviate the ‘weeds trade-off’ described in
section A.II. This system is intended to modify ‘conventional’ cropping systems of
industrialized countries dominated by short crop rotations or monocultures of annual cash
crops (e.g. cereals, rapes, maize, beets), by combining several of the elements introduced in
the preceding section A.III. This concept is based on the ‘temporal separation’ strategy
(section A.III.7) involving a long crop rotation comprising three phases:
1) periods (several years) of high yielding annual cash crops (production function),
2) periods (several month) favourable to different elements of farmland biodiversity and
the physical environment such as over-winter stubble fields (followed by spring or summer
sown crops), rotational set-asides, or other appropriate ‘agro-environment schemes’
concerning the whole field, and
3) periods of pluriannual crops (such as PFCs, c.f. section A.III.9, forage or biomass
production) that may have a regulating function on weed populations adapted to annual crops
(weed regulation function, detailed in section A.IV above) and may also be favourable to the
environment (see section A.V.3 below) and several components of farmland biodiversity (see
section A.V.2 below).
An exemplary crop rotation including these three phases is illustrated in the upper part of Fig.
7. On the landscape scale, the three periods should form a dynamic mosaic (c.f. section A.III.7
and Fig. 5). During the annual crop phase (1), curative weed control would be reduced,
especially the use of herbicides, to limit their different draw-backs (c.f. section A.II.2). Weeds
are primarily managed by a combination of alternative preventive and curative techniques in
the framework of Integrated Weed Management (IWM, see A.III.2). Herbicides should only
be used if other IWM-techniques are not sufficient. Herbicide application is thus limited to
some years and some crops, which should also reduce the risk of selecting resistant weed
biotypes. Moreover, farmers should prefer herbicide types (a) with narrow spectra targeting
mainly problematic weed species that can not be well controlled by other means, (b) with low
toxicity to other organisms and (c) quick degradation.
The modified system based on such a spatio-temporal separation of different agro-ecological
functions may have strong impacts on weeds (see section A.IV above), but also on other
elements of farmland biodiversity, the physical environment and crop yields & economic
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