Bio-based composite granules with simultaneous biocontrol and phosphorus fertilization roles: outcomes from a lab-scale in-vitro assessment

The use of phosphate rocks as low-solubility phosphorus fertilizers has been promoted to reduce the environmental impacts of agriculture, but adequate nutrient uptake by plants depends on solubilization of the rock, driven by soil microorganisms. Here, investigation was made of the microbial solubilization of low-solubility phosphate rocks, together with simultaneous bioprotective action involving the biocontrol of microorganisms. The aim was to enhance function and value by delivering two effects using a single bio-based product, in accordance with the concept of a "bioreactor-in-a-granule" system. A composite structure was developed, based on a starch matrix, comprising a combination of Trichoderma asperelloides, as a biocontrol agent, and Aspergillus niger, as an acidulant. A significant increase of up to 150% in P solubilization was achieved, indicating the positive effect of the microorganism-composite interaction. In vitro assays showed that the ability of T. asperelloides to inhibit Fusarium oxysporum mycelial growth was maintained in the presence of A. niger. Moreover, the estimated cost of the composite granule (0.35 US$/kg of product on a dry basis) revealed competitive. The results indicated that the association of T. asperelloides and A. niger is an effective way to increase nutrient availability and to inhibit plant pathogens, opening up possibilities for the design of multifunctional bio-based fertilizer composites. This article is protected by copyright. All rights reserved.

Unveiling the Solubilization of Potassium Mineral Rocks in Organic Acids for Application as K-Fertilizer

Organic acids produced by soil microorganisms can be useful to promote the release of potassium (K) from potassium mineral rocks (KR), but the complexity of low reactivity minerals limits K solubilization and their use as fertilizer. Here, we investigate the ways that different organic acids (gluconic, oxalic, and citric) can affect the solubilization of potassium minerals, in order to propose process strategies to improve their solubility. For this, evaluations were performed using the model minerals KR_polyhalite (sedimentary mineral), KR_feldspar (igneous mineral), and KCl (commercial fertilizer). For KCl and KR_polyhalite, complete solubilization was achieved using all the organic acids, while for KR_feldspar, the highest K⁺ solubilization (34.86 mg L^-1) was achieved with oxalic acid. The solubility of KR_feldspar was further investigated under submerged cultivation with the filamentous fungus Aspergillus niger, as well as after a mechanochemical grinding treatment. The biotechnological route resulted in solubilized K up to 63.2 mg L^-1. The mechanochemical route, on the other hand, increased the release of K by about 8.6 times (993 mg L^-1) compared to the natural mineral, due to the greater fragmentation of the particles after the treatment (with a surface area about 2.5 times higher than for the in natura KR_feldspar). These findings demonstrated the potential of applying biotechnological and mechanochemical routes with organic acids to improve the solubilization of K present in low reactivity mineral rocks, indicating the possible use of these minerals in more sustainable agricultural practices.

AVANÇOS NA PRODUÇÃO E FORMULAÇÃO DE INOCULANTES MICROBIANOS VISANDO UMA AGRICULTURA MAIS SUSTENTÁVEL

ADVANCES IN THE PRODUCTION AND FORMULATION OF MICROBIAL INOCULANTS FOR A MORE SUSTAINABLE AGRICULTURE. The wide application of beneficial microorganisms in agriculture as inoculants to combat pests and diseases and/or to improve soil fertility and the nutrients availability for plants has been considered as an effective and more sustainable alternative than chemical fertilizers and agricultural defensives. However, it is necessary to examine all processing steps of these bio-based products under a more integrated view including the type of microorganisms and the whole production process in order to reduce dependence on synthetic chemical inputs. Here, recent developments on the production and formulation technologies of microbial inoculants and the main types of inoculants currently applied in agriculture are addressed. The different types of microbial formulations are compared with emphasis on the encapsulation technology. Moreover, the application of biofertilizers in seed coating and a new approach to apply biocomposites as fertilizers are discussed, presenting the main challenges and future perspectives to promote more sustainable agriculture practices.

Carbon nanotubes as supports for inulinase immobilization

The commercial inulinase obtained from Aspergillus niger was non-covalently immobilized on multiwalled carbon nanotubes (MWNT-COOH). The immobilization conditions for the carbon nanotubes were defined by the central composite rotational design (CCRD). The effects of enzyme concentration (0.8%–1.7% v/v) and adsorbent:adsorbate ratio (1:460–1:175) on the enzyme immobilization were studied. The adsorbent:adsorbate ratio variable has positive effect and the enzyme concentration has a negative effect on the inulinase immobilization (U/g) response at the 90% significance level. These results show that the lower the enzyme concentration and the higher the adsorbent:adsorbate ratio, better is the immobilization. According to the results, it is possible to observe that the carbon nanotubes present an effective inulinase adsorption. Fast adsorption in about six minutes and a loading capacity of 51,047 U/g support using a 1.3% (v/v) inulinase concentration and a 1:460 adsorbent:adsorbate ratio was observed. The effects of temperature on the immobilized enzyme activity were evaluated, showing better activity at 50 °C. The immobilized enzyme maintained 100% of its activity during five weeks at room temperature. The immobilization strategy with MWNT-COOH was defined by the experimental design, showing that inulinase immobilization is a promising biotechnological application of carbon nanotubes.