The soil is a complex system where processes have direct influence on crop nutrition and plant health. Unfortunately, most of the agricultural soil management practices, compact them producing poor oxygenation, low benefic microorganism populations and metabolic disorders in plants. Those factors induce abnormal plant development and predisposition to the attack of soil borne plant pathogens as: Sclerotium cepivorum, Sclerotium rolfsi, Sclerotinia sclerotiorum, Rhizoctonia solani, Rosellinia spp. But also, some air borne pathogens as Colletotrichum sp., are more aggressive under those conditions. In Costa Rica some practical trails done by farmers, have shown that the addition of Trichoderma spp. to organic fertilizers like vermicompost, Bocashi, and other composts, has a positive effect on the structure and microbial diversity, that improves nutrient movement in plants and pathogen suppression. Vegetative material of leather fern (Rumohra adiantiformis) infected by Rosellinia spp., planted with bocashi amended with. T. asperellum (T. harzianum), showed more tip root growth and new fern rhizomes. Also the plants produced higher number of fiddleheads and high quality fronds. Non-treated material showed a total loss.
In some leaf vegetables as lettuce the use of vermicompost followed by Trichoderma viride application, inhibited S. sclerotiorum development on the crop, in this study sclerotia were infected and plant yields were increased. Compost previously inoculated with Trichoderma, inhibited 100% the Botrytis and R. solani infection, in nurseries, and plant nutrition was improved. The observed results are attributed to the antagonistic effect of Trichoderma on soil and airborne pathogens, production of growth regulators, solubilization of some microelements and better mineral absorption with the development of more roots and elimination of diseased roots. As conclusion, the organic substrates inoculated with Trichoderma spp., besides the organic matter source, they improve the structural characteristics of soil, promote the biochemical processes, increases the level of growth regulator substances and inhibit plant disease as well.