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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iv) the availability of cheap and efficient mineral fertilizers, herbici<strong>de</strong>s and pestici<strong>de</strong>s<br />
that substituted some of the beneficial effects of perennial <strong>crop</strong>s on the following<br />
annual <strong>crop</strong>s (Entz et al., 2002; Katsvairo et al., 2006b).<br />
A.IV EXPECTED IMPACTS OF PERENNIAL CROPS ON WEEDS<br />
A.IV.1 Literature review<br />
Empirical studies investigating the impacts of perennial <strong>crop</strong>s on arable weeds are very<br />
heterogeneous in terms of methodology and not so frequent, probably as the importance of<br />
this <strong>crop</strong> type <strong>de</strong>creased during the 20th century. In this review, studies were found mainly by<br />
using the following key words in popular search engines such as the ‘ISI web of knowledge’<br />
(www.isiknowledge.com) and ‘Google Scholar’ (http://scholar.google.com): “<strong>crop</strong> rotation”,<br />
“<strong>temporary</strong> grassland”, “forage”, “fod<strong>de</strong>r”, “ley”, “mixed farming”, “alfalfa”, “lucerne”,<br />
“clover”, “legume-grass mixture”, “weed management”, “weed community”, “<strong>crop</strong><br />
protection” and by searching both the references cited in these studies and younger articles<br />
citing them. The review was limited to <strong>crop</strong>ping systems in temperate climates and to papers<br />
published after 1992, thus not inclu<strong>de</strong>d in the review of Liebman & Dyck (1993).<br />
There are numerous studies comparing weed infestations in different <strong>crop</strong> <strong>rotations</strong>. However,<br />
most studies inclu<strong>de</strong> only annual <strong>crop</strong>s. This may also be illustrated by the fact that 26 out of<br />
29 comparisons between <strong>rotations</strong> and monocultures reviewed by Liebman & Dyck (1993),<br />
<strong>crop</strong> <strong>rotations</strong> inclu<strong>de</strong>d only annual <strong>crop</strong>s. In the literature search, 15 more recent studies<br />
reporting impacts of PFCs on weeds (sometimes <strong>de</strong>scribed by several successive publications)<br />
were retained. These studies will be shortly reviewed in the following (see also the summary<br />
in Table 1 of Article 1). 13 studies were based on field experiments, only one study on a weed<br />
survey covering a large number of fields of a whole region and one study on interviews of<br />
farmers.<br />
A.IV.1.1 Farmers interview<br />
Entz et al. (1995) interviewed 253 farmers known to inclu<strong>de</strong> forages in their <strong>crop</strong> <strong>rotations</strong> in<br />
two regions of Canada, Manitoba and Saskatchewan in 1992. 67% of them reported yield<br />
benefits and 83 % weed control benefits from including forages in their <strong>rotations</strong>. Weed<br />
control benefits lasted for one (11% of respon<strong>de</strong>nts), two (50% of respon<strong>de</strong>nts), or more (33%<br />
22