Adequate design of control treatments in long term agroforeestry experiments with multiple objectives |
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| Authors: | C Dupraz |
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| Institution: | (1) INRA, Lepse, Place Viala, 34060 Montpellier, France |
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| Abstract: | Agroforestry experiments usually include control plots of either pure crop or pure tree stands. A clear distinction should
be made between intensively managed biophysical controls and farming system controls with realistic labour input and management
regimes. Trying to draw biophysical conclusions from farming system controls (or the reverse) is often not justifiable. The
design and management of these elusive control plots is a complicated issue which is often overlooked. Many factors beyond
the control of the experiment manager can disturb long term field agroforestry experiments. Some examples from French agroforestry
experiments illustrate how uncontrolled factors may bias the results, including the proportion of harvested to planted trees,
the weeding regimes, and the use of tree- shelters. The analysis of agroforestry data could be more efficient when considering
a continuum of tree – crop mixture management options between the agroforestry plot and the non agroforestry plot. The concept
of biophysical control plots becomes then less essential. A relevant modelling approach of interactions between trees and
crops should 1) perform correctly for any tree/crop proportion and even for pure stands, when setting the parameters of the
other component to zero, 2) provide for the inclusion of new, uncontrolled factors that could emerge through time. The biological
efficiency of agroforestry systems may however be a subordinate criterion for agroforestry adoption, as observed at the moment
in France. Agroforestry systems with poor biological outcomes can even be very attractive in some ecological or sociological
conditions, and only farming system controls may bring this aspect to light.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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| Keywords: | competition experiment design farming system resource capture tree density weeds |
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