Peat replacement is an increasing demand in containerized and transplant production, due to the environmental constraints associated to peat use. However, despite the wide information concerning the use of alternative materials as substrates, it is very complex to establish the best materials and mixtures. This work evaluates the use of mixture design and surface response methodology in a peat substitution experiment using two alternative materials (green compost and palm fibre trunk waste) for transplant production of tomato (Lycopersicon esculentum Mill.); melon, (Cucumis melo L.); and lettuce (Lactuca sativa L.) in organic farming conditions. In general, the substrates showed suitable properties for their use in seedling production, showing the best plant response the mixture of 20% green compost, 39% palm fibre and 31% peat. The mixture design and applied response surface methodology has shown to be an useful approach to optimize substrate formulations in peat substitution experiments to standardize plant responses.

A three-year field experiment was conducted in a Mediterranean environment on lettuce to study the production, characteristics and possible use of different amendments as substitution for nitrogen mineral fertilizers. The effects on soil dynamics were also investigated. The following treatments supplying 140 kg N ha⁻¹ were compared: Stabilized anaerobic digestate from wine distillery wastewater (SAD); Non-stabilized organic material from wine distillery wastewater (NSAD); Olive pomace compost (OPC); Mineral N fertilizer (MIN); Commercial organic fertilizer (CORG). These treatments were compared with an unfertilized control (CONTR). No significant reduction occurred with SAD as compared to MIN, but its application significantly increased marketable yield in all experimental years compared to the unfertilized control. Furthermore, SAD treatment reached the highest marketable yield with an increase of 52.9% compared to CONTR in the year characterized by high unevenly rainfall distribution. Even with low absolute values, the application of mineral fertilizer not only had the highest level of nitrate in the leaves but also determined higher value of soil mineral N compared to by-products treatments, thereby increasing pollution risks. The NSAD and the OPC treatments had significantly lower biomass and marketable yield than MIN and presented the highest soil N mineral deficit. As a consequence, the choice and the production of the more appropriate agroindustrial by-product (in our research SAD treatment) is crucial to ensure lettuce yield and the sustainability of agro-ecosystem.

A 2-year field experiment was carried out in a Mediterranean environment to study the effects of vetch ( Vicia sativa L.) residue management strategies incorporating green manure (GM) using a roller-crimper (RC) and different organic fertilizers (municipal solid waste compost, anaerobic digestate, and a commercial organic fertilizer) on organic zucchini ( Cucurbita pepo L.) yield and quality. Zucchini yield was influenced positively by the vetch residue management strategy, although the response was significantly different between years. The vetch cover crop increased marketable zucchini yield in the first year by 46.6% compared with the fallow (FA) treatment, indicating that this fertility-building crop could reduce off-farm nitrogen (N) fertilizer input for subsequent crops. Averaging over 2 years of the experiment, marketable zucchini yield increased by 15.2% and 38% with the RC mulch and GM plow-down, respectively, compared with the FA treatment, although differences were significant in the first year only. The application of organic fertilizers in vetch management plots increased marketable zucchini yield by 21.8% in the first year compared with the unfertilized control. This result is particularly relevant, because organic fertilizers were applied at ≈50% of the normal application rate for zucchini after taking into account biological N fixation attributable to the vetch. The concentrations of soil mineral N at harvest were 19, 27, and 28 mg·kg ⁻¹ for the RC, FA, and GM treatments, respectively. These mineral N concentrations indicated that a portion of applied organic fertilizer N, and N attributable to vetch (GM and RC), remained in the soil at harvest, suggesting the potential for leaching, which should be taken into account in the overall fertilization program. These research findings suggest that effective vetch cover crop management and the application of organic fertilizers can improve yield and quality of organically managed zucchini.