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