A simple technique for assessing the cuticular diffusion of humic acid biostimulants

Enhancing Lettuce Yield through Innovative Foliar Spray of Biopolymers Derived from Municipal Biowastes

Municipal waste biomass could be valorized as an alternative feedstock to produce compounds beneficial for agricultural applications. The foliar spray application of biostimulants emerges as a promising and innovative technique due to its environmental safety and ability to enhance crop yields. In recent years, the exploitation of biopolymers obtained through alkaline hydrolysis of the solid anaerobic digestate from municipal biowastes has attracted researchers' interest. The aim of this study is to investigate the effects on lettuce growth of a product obtained through alkaline hydrolysis from municipal biowaste, Biopolymers (BPs), and of a derivate subjected to a further oxidation process, Biopolymers Oxidate (BPs OX). The effects of the treatments at various concentrations were evaluated by monitoring plant growth and observing the trends in the activities of the main enzymes involved in the nitrogen metabolic pathway of lettuce. Results suggest that the best treatments in terms of fresh weight were achieved by using BPs at 10 mg/L and BPs OX at 100 mg/L, increasing yield by around 28% and 34%, respectively. The innovative aspect of this work was to make easier for farmers the biopolymers application by testing a foliar spray methodology for BPs and BPs OX, which has never been tested before in any crop.

Functional Hydrogels for Agricultural Application

Ten different hydrogels were prepared and analyzed from the point of view of their use in soil. FT-IR spectra, morphology, swelling ability, and rheological properties were determined for their characterization and appraisal of their stability. The aim was to characterize prepared materials containing different amounts of NPK as mineral fertilizer, lignohumate as a source of organic carbon, and its combination. This study of stability was focused on utility properties in their application in soil-repeated drying/re-swelling cycles and possible freezing in winter. Lignohumate supported the water absorbency, while the addition of NPK caused a negative effect. Pore sizes decreased with NPK addition. Lignohumate incorporated into polymers resulted in a much miscellaneous structure, rich in different pores and voids of with a wide range of sizes. NPK fertilizer supported the elastic character of prepared materials, while the addition of lignohumate shifted their rheological behavior to more liquid. Both dynamic moduli decreased in time. The most stable samples appeared to contain only one fertilizer constituent (NPK or lignohumate). Repeated re-swelling resulted in an increase in elastic character, which was connected with the gradual release of fertilizers. A similar effect was observed with samples that were frozen and defrosted, except samples containing a higher amount of NPK without lignohumate. A positive effect of acrylamide on superabsorbent properties was not confirmed.

How the Supramolecular Nature of Lignohumate Affects Its Diffusion in Agarose Hydrogel

Lignohumate, as an industrially produced analog of natural humic substances, is studied from the point of view of its diffusion properties. This work focuses on its permeation ability, important in agricultural and horticultural applications, connected with its penetration into plant organs as leaves and roots. The hydrogel based on agarose was used as a model material for the diffusion of lignohumate. Two types of experiments were realized: the diffusion of lignohumate in the hydrogel diffusion couple and the diffusion of lignohumate from its solution into hydrogel. The diffusion coefficient of lignohumate in the hydrogel was determined and used for the modelling of the time development of concentration profiles. It was found that the model agrees with experimental data for short times but an accumulation of lignohumate in front of the interface between donor and acceptor hydrogels was observed after several days. The particle size distribution of lignohumate and changes in the E₄/E₆ ratio used as an indicator of molecular weight of humic substances were determined. The results showed that the supramolecular structure of lignohumate can react sensitively to actual changes in its environs and thus affect their mobility and permeability into different materials. A filtration effect at the interface can be observed as an accompanying phenomenon of the re-arrangement in the lignohumate secondary structure.

From Lab to Field: Role of Humic Substances Under Open-Field and Greenhouse Conditions as Biostimulant and Biocontrol Agent

The demand for biostimulants has been growing at an annual rate of 10 and 12.4% in Europe and Northern America, respectively. The beneficial effects of humic substances (HS) as biostimulants of plant growth have been well-known since the 1980s, and they can be supportive to a circular economy if they are extracted from different renewable resources of organic matter including harvest residues, wastewater, sewage sludge, and manure. This paper presents an overview of the scientific outputs on application methods of HS in different conditions. Firstly, the functionality of HS in the primary and secondary metabolism under stressed and non-stressed cropping conditions is discussed along with crop protection against pathogens. Secondly, the advantages and limitations of five different types of HS application under open-fields and greenhouse conditions are described. Key factors, such as the chemical structure of HS, application method, optimal rate, and field circumstances, play a crucial role in enhancing plant growth by HS treatment as a biostimulant. If we can get a better grip on these factors, HS has the potential to become a part of circular agriculture.