Apricot Root Development and Morphology as Influenced by Mulching and Multispecies Ground Cover

In temperate environments, characterized by a winter rainy season and a dry summer, roots of perennial fruit crops in a clay soil tend to concentrate in the shallowest layer and diminish exponentially with soil depth. The top 10 cm of the soil profile also have the highest concentration of herbaceous roots. Soil management techniques influence interspecific root competition and can modify surface soil properties. In a field experiment in a five-year-old apricot orchard (Prunus armeniaca L. 'Bella d'Imola', grafted on Prunus cerasifera (Mir 29C)), two different soil management strategies widely used in organic farming were compared: multi-species ground cover, and organic mulching. Treatments were applied in the tree row where plant root growth was monitored through 21 rhizotron windows per treatment, over a period of 26 months. Competition with multi-species ground cover decreased apricot root growth in the top 20 cm of the soil profile, while tree root development was enhanced by multi-species ground cover at lower depths. Tree roots were also significantly thicker in this management technique. The presence of multi-species ground cover roots increased the volume of soil explored by tree roots, with more, thicker pioneer roots with explorative function. Tree root growth in the surface soil was generally reduced, thus preventing roots from invading previously occupied niches. In the short term, organic mulch suppressed grass growth and resulted in a reduction of interspecific competition and a lower tendency of the tree root system to transmigrate. The effect of multi-species ground cover competition in the surface soil lessened with time, suggesting that over time the relative performance of the two treatments may shift due to changes in soil mechanical and biochemical characteristics and to tree root self-competition.