Soil biodisinfestation is the process generated after the incorporation of organic amendments followed by a plastic cover to control soilborne diseases. Among organic amendments, the use of agricultural by-products could be an interesting alternative as it promotes circular economy. In this study, beer bagasse and defatted rapeseed cake together with fresh cow manure were incorporated into the soil (1.5, 0.5, and 20 kg/m2, fresh weight, respectively) to assess their capacity to reduce disease incidence caused by the root-knot nematode Meloidogyne incognita in protected lettuce crops and develop suppressive soils. The trial was conducted in a commercial greenhouse for 7 weeks during which temperature was continuously recorded at three different soil depths (15, 30, and 45 cm). Short- and long-term effects were assessed: before treatment, after treatment, after first crop post-treatment and one year post-treatment. Disease incidence and changes in nematode community structure were analyzed along with microbiological properties and general physicochemical parameters. After biodisinfestation, microbiological activity significantly increased in the treated soils and changes in the nematode community structure were detected in detriment of M. incognita and other plant-parasitic nematodes. These effects were more apparent after the first crop post-treatment than right after biodisinfestation. In the first crop after biodisinfestation, lettuce yield increased in the treated plots and root galling indices were significantly lower. One year after treatment, differences between treatments could be observed in the incidence of the damage caused by M. incognita that remained lower in the treated plots. In this trial, the addition of beer bagasse and rapeseed cake along with fresh manure in biodisinfestation treatment demonstrated nematicidal effects against M. incognita. Moreover, we suggest that the compounds released during the degradation of these by-products and the sub-lethal temperatures achieved in this trial during biodisinfestation (<42°C) were the key to develop suppressive soils in the long-term.

One of the major challenges in biodisinfestation treatments against soilborne pathogens is the selection of the proper organic amendments and mixture features. The use of agro-industrial by-products is a sustainable alternative with proven efficacy, but the availability has to be considered in terms of location and quantity. Sunflower seed is one of the five major oil crops widely cultivated and the husk constitutes a significant part that is discarded. This by-product brings together the features to be considered an interesting organic amendment in agricultural soils because of its lignocellulose content, but no references have been found in this field. In this study, sunflower seed husk was used with fresh cow manure in biodisinfestation treatments, alone or combined with other by-products (rapeseed cake, beer bagasse and wheat bran). The assay was performed in summer in a commercial greenhouse with significant yield losses in lettuce crops caused by the root-knot nematode Meloidogyne incognita. Four different amendment mixtures were applied which included 3kg/m2 cow manure, as common waste, and 1 kg/m2 of by-products (dry weight), considering 6mgC/g soil in all treatments but different C/N ratio (23, 29, 31, 34) and by-products. Data was collected in three moments: (i) before and (ii) after biodisinfestation treatments and (iii) after harvesting the first crop after biodisinfestations. Crop damage was assessed through root galling index and the number of eggs in roots. The effects on the pathogen population and the whole soil nematode community were assessed along with some physicochemical and soil microbiological variables (respiration rate, microbial organic C, water-soluble organic C and physiological profile of heterotrophic bacteria through Biolog Ecoplates™). All treatments reported effectiveness in disease control without significant differences among them, but among times. However, soil temperatures during biodisinfestations were higher at higher C/N ratios and fertility variables also increased in these cases, mainly in the treatment with husk as the only by-product. Sunflower seed husk proved to be an interesting source of organic C to improve both biodisinfestation treatments and soil fertility in humid temperate climate zones.