MANAGING SOILS TO ENHANCE MYCORRHIZAL BENEFITS IN MEDITERRANEAN AGRICULTURE

Regions with Mediterranean climates (i.e., with winter rainfall and su mmer drought) have many different agricultural systems. However, two c ommon features of these regions are the use of rotations of legumes an d cereals, and the relatively low levels of use of phosphate fertilize r applied to phosphate-deficient soils. There is potential to increase the efficiency of use of phosphate in these environments by increasin g the contribution of vesicular arbuscular (VA) mycorrhizal fungi beca use legumes respond to mycorrhizal colonization when phosphate is limi ting plant growth. The potential to make effective use of the mycorrhi zal symbiosis in Mediterranean agriculture depends on developing furth er understanding of several key relationships between the components o f the symbiosis and the soil conditions. First, there is a need to kno w whether the existing level of colonization of roots by mycorrhizal f ungi is less than optimal. To achieve this, a combination of an unders tanding of the effects of agricultural practices (as they affect the d ynamics of populations of the fungi in soil) and a calibrated bioassay to predict the level of colonization of roots in the following season are required. The second relationship required is the interaction bet ween the rate and extent of colonization of roots and the functioning of the mycorrhizas. The impact of agricultural practices on the functi oning of the symbiosis also needs to be included in the analysis.