Soil physical characteristics and understory management in a walnut (Juglans regia L.) plantation in central Italy

Early and significant influences on soil physical properties are expected i n temperate agroforests as a consequence of various soil and/or understory management practises. Soil physical characteristics were studied in an agro forestry trial of common walnut (Juglans regia L.) set up on a volcanic soi l in central Italy, where clean cultivation, polyethylene mulching along tr ee rows and intercropping of walnut with alfalfa (Medicago sativa L.) were tested. Soil total porosity, size distribution and morphology of pores, and available water were evaluated during the second and the fourth growing se ason of the plantation to determine the possible influence and duration of the treatments on soil physical properties. In the first sampling the total porosity was two to three times greater than in the second one and no sign ificant differences were found between treatments. Seasonal variation in to tal porosity was observed, with a maximum in summer. All dimensional classe s of pores < 50 mu m were well represented, thus indicating an adequate soi l structure. In the fourth growing season total porosity and pore size dist ribution were very similar in clean cultivation and mulching so that the mu lching effect on the structural characteristics of this soil was equivalent to that of repeated rototilling in clean-cultivated plots. Moreover, mulch ing stimulated more biological activity, resulting in a higher proportion o f rounded pores. Alfalfa roots created a more homogeneous environment to a depth of 35 cm, with a greater presence of elongated pores in the range 50- -500 mu m that could make movement of water easier. Most of the water retai ned was unavailable for plants, so that competition between walnuts and alf alfa took place and could be associated with the lower stem growth of inter cropped walnuts.