Considering the desirable complementary use ofwater and
nutrient resources in agroforestry systems by trees and crops
van Noordwijk et al. (1996) stated that a nutrient uptake from
deeper horizons only occurs if at least a limited resource
is available in the subsoil. On the experimental site the
prevailing precipitation regime does not allow an extended
infiltration, retention and storage of water in the subsoil. The
availability of nutrients is limited to the application of fertiliser
generally stimulating root growth in the topsoil. Hence, low
water and nutrient resources do not favour root proliferation
in deeper soil layers. Thus, the coinciding root growth and the
periodical occurrence of competition between R. pseudoacacia
and M. sativa at the Lusatian study site may be well explained.
With regard to the combination of an N-fixing species with
a non-N-fixing species, the observed intermingling root system
of trees and crops can be advantageous. Such a rooting
pattern favours that N provided by the N-fixing species can be
used by the non-N-fixing species (Schroth, 1999).