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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significantly reduce the variability of the farmers’ income, which may be more important<br />
than the absolute amount of income (Zentner cited in Entz et al., 2002).<br />
• In a study of Olesen et al. (2002) in Denmark, the yield benefits caused by the inclusion of<br />
a grass-clover ley could not fully compensate for the yield reduction as a result of leaving<br />
25 % of the rotation out of cash <strong>crop</strong> (cereal) production.<br />
• In a study of Liebman et al., (2008), the economic profitability of the farming system<br />
could be improved by including alfalfa <strong>crop</strong>s into corn–soybean <strong>rotations</strong>, but the<br />
government subsidies reduced this advantage from 7 % to 1 %.<br />
The need for (and therefore the prices of) herbal forages <strong>de</strong>creased during the last <strong>de</strong>ca<strong>de</strong>s due<br />
to the separation of <strong>crop</strong> and livestock production and the shift towards grain forage such as<br />
maize. In the future, the <strong>de</strong>mand and profitability of perennial <strong>crop</strong>s might however increase<br />
again as these kind of <strong>crop</strong>s are increasingly used to produce energy or raw materials for<br />
different industries. Tilman et al., (2006) suggested that ‘Low-Input High-Diversity’<br />
<strong>grasslands</strong> may produce biomass (e.g. for bio-fuels) <strong>with</strong> a negative carbon balance and higher<br />
yields compared to different monocultures.<br />
A.VI THE RESEARCH PROJECT<br />
A.VI.1 Objectives and questions<br />
The diversified <strong>crop</strong>ping system proposed in section A.V should alleviate the ‘weeds tra<strong>de</strong>off’<br />
and contribute towards a more sustainable agriculture. This system relies on the ‘weed<br />
regulation function’ of PFCs. It is thus most essential to study the impacts of perennial <strong>crop</strong>s<br />
on weeds and to test the hypothesis of weed community shifts away from species that are most<br />
noxious in annual <strong>crop</strong>s. It is also necessary to improve the un<strong>de</strong>rstanding of the un<strong>de</strong>rlying<br />
mechanisms (Table 4). This is essential to predict the impacts on weed populations and<br />
community dynamics and to successfully use this hypothetical ‘ecosystem service’ provi<strong>de</strong>d<br />
by perennial <strong>crop</strong>s. The following research questions will therefore be addressed in this thesis:<br />
• How do weed populations and communities react to PFCs?<br />
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