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

annual crops while increasing organic matter and carbon sequestration in the soil (Sebillotte,
1980; Viaux et al., 1999; Eltun et al., 2002; Entz et al., 2002). Moreover, nitrogen fixing
legume species included in the PFC mixtures may reduce the need nitrogen fertilisation in the
grassland and in the following annual crops improving the energy efficiency of the system
(Entz et al., 2002). However, the organic matter and nutrients accumulated during the period
of the perennial crop may only partly be used by the following annual crops, while other parts
may be lost through leaching, especially if the temporary grassland is terminated by deep
ploughing (Viaux et al., 1999).
A.V.4 Expected impacts on crop production
Introducing perennial crops into crop rotations may have various (positive and negative)
impacts on crop yields and farm profitability. The economic profitability of perennial crops
may be lower than for annual (cash) crops due to lower marked prices. The low economical
value of forage biomass might however be partly compensated for by rather low production
costs (Bulson et al., 1996; Entz et al., 2002). Moreover, perennial crops create other long-term
amenities, including improvements of soil structure and fertility and reductions in pest
pressures (Entz et al., 2002; Katsvairo et al., 2006a). Therefore, perennial crops may also lead
to significant yield increases and savings of fertilizer and pesticide inputs in the subsequent
annual crops. In addition to these variations, public subsidies may favour or penalize perennial
crops. In Iowa, USA, perennial alfalfa get lower subsidies than annual crops such as corn and
soy bean (Liebman et al., 2008). In the European Union, all crop types should get the same
amount of subsidies (‘decoupling’) since the application of the 2003 CAP reform (which may
differ in the member states). In some European countries or regions, mixed farming systems
may even profit from specific subsidies in the framework of the ‘second pillar’ of the CAP.
The importance of the different impacts on crop yields and farm profitability will depend on
climatic, agronomic, economic and politic factors and may thus strongly differ between
regions and farming systems. The three studies cited in the following have thus only an
exemplary character.
• A Canadian study suggests that production cost of forage-based systems was lower than
for continuous grain production systems but higher than a wheat-fallow system.
Interestingly, including a 2- or 3-year forage crop in a 6-year rotation was found to
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