Leonardites Rich in Humic and Fulvic Acids Had Little Effect on Tissue Elemental Composition and Dry Matter Yield in Pot-Grown Olive Cuttings

The use of humic substances in agriculture has increased in recent years, and leonardite has been an important raw material in the manufacture of commercial products rich in humic and fulvic acids. Leonardite-based products have been used to improve soil properties and to help plants cope with abiotic and biotic stresses. In this study, the effects of two commercial leonardites and an organic compost, in addition to a control treatment, were assessed for pot-grown olive plants over a period of fourteen months on soil properties, tissue elemental composition and dry matter yield (DMY). Three organic amendments were applied at single and double rates of that set by the manufacturer. The study was arranged in two experiments: one containing the seven treatments mentioned above and the other containing the same treatments supplemented with mineral nitrogen (N), phosphorus (P) and potassium (K) fertilization. Overall, organic compost increased soil organic carbon by ~8% over the control. In the experiment without NPK supplementation, N concentrations in shoots and P in roots were the highest for the compost application (leaf N 12% and root P 32% higher than in the control), while in the experiment with NPK supplementation, no significant differences were observed between treatments. Total DMY was ~10% higher in the set of treatments with NPK in comparison to treatments without NPK. Leonardites did not affect significantly any measured variables in comparison to the control. In this study, a good management of the majority of environmental variables affecting plant growth may have reduced the possibility of obtaining a positive effect on plant nutritional status and growth from the use of commercial leonardites. The leonardites seemed to have caused a slight effect on biological N immobilization. This is not necessarily an advantage or a drawback; it is rather a feature that must be understood to help farmers make better use of these products.

Different Organic Fertilisation Systems Modify Tomato Quality: An Opportunity for Circular Fertilisation in Intensive Horticulture

The valorisation of vegetal waste as a source of crop nutrients constitutes a circular strategy to improve the sustainability of intensive horticultural production systems. The main goal of this study was to evaluate the effects of organic amendments derived from vegetal residues on the yield and quality of tomato. The following fertilisation treatments were carried out: fresh vegetal residues (4 kg m−1), compost (3 kg m−1), and vermicompost at two different doses (3 and 9 kg m−1), all derived from previous tomato crop vegetal residues, an organic treatment with goat manure (3 kg m−1), and a control mineral fertigation treatment. The highest yield was obtained with conventional mineral fertigation management, followed by vermicompost treatments at two different doses (3 and 9 kg m−1), with no statistical differences. The organic treatments with fresh crop residues, compost and goat manure resulted in lower yield. Regarding quality parameters, the lycopene content was higher in the mineral fertilisation and vermicompost at 3 kg m−1 treatment, while the other antioxidants measured were more concentrated in tomatoes fertilised with vermicompost treatment at 9 kg m−1 and goat manure. The plant nutrient management with vermicompost is the best circular solution, as it allows to reintegrate the residues generated in previous crop cycles into the soil, obtaining a yield equal to chemical input management and tomatoes with high nutritional quality.