Effects of soil solarization and Trichoderma on strawberry production

Soil solarization and Trichoderma, alone and combined, were tested in three consecutive annual production cycles in Huelva (southwestern Spain) an environment representative of the coastal strawberry production area, to evaluate the effectiveness in enhancing strawberry yield and the relationship between Trichoderma soil population, root colonization by Trichoderma, yield and root weight. Solarization was conducted during the summer, using clear 50 μm low-density polyethylene mulch. Trichoderma spp. were applied via drip irrigation and dip, adding to the soil 7-days before planting (108 conidia/m2), and strawberry roots were dipped in a suspension of Trichoderma (106 conidia/ml) prior to planting. Mean soil temperatures in solarized plots averaged 46 °C at 5 cm depth, 43 °C at 10 cm, and 38 °C at 20 cm. Solarization reduced Trichoderma soil populations. Nevertheless, Trichoderma soil populations increased over the three consecutive years in solarized plots, and no differences were observed after three repeated treatments of the same site. Solarization did not significantly reduce root colonization by Trichoderma. Combination of solarization with Trichoderma applications significantly increased Trichoderma soil populations relative to the solarization alone treatment, and root colonization by Trichoderma compared to the untreated control and the solarization alone treatment. Soil solarization, alone or combined with Trichoderma applications, increased strawberry yield 77.6% and 78.2% in year 2, and 11.0% and 43.2% in year 3, respectively. Trichoderma spp. became established in soil, and by the end of each season it could be recovered from soil samples and from root segments. Trichoderma applications increased Trichoderma soil populations, root colonization, root weight and strawberry yield 84.9% in year 2 and 17.6% in year 3. Significant positive correlations were observed between Trichoderma soil populations and strawberry yield, and between Trichoderma soil populations and root colonization by Trichoderma.