Revealing the Structure Formation on Polyglycerol Citrate Polymers-An Environmentally Friendly Polyester as a Seed-Coating Material.

A detailed structural investigation of a promising bio-based polymer, polyglycerol citrate polyester, obtained by the bulk polycondensation of glycerol (Gly) against citric acid (Cit) under mild reaction was performed. The reaction in conditions with and without catalyst use (sulfuric acid, H2SO4) was investigated, showing evidence that it is possible to modify the polymer solubility according to the ratio and catalyst utilization. 13C and 1H NMR indicated that synthesis catalyzed with Cit excess leads to higher esterification degrees of citrate groups. In contrast, the Gly moieties are more prominent in catalyzed polymers regardless of the excess monomers. Overall, a successful conversion of Gly and Cit into polyesters was attained even without catalysis, enabling a simple route for the large-scale production of this green material to be used as a coating material. This polymer has been shown to be well-suited for coating seeds and might be a promising material for similar agricultural applications. Tests on soybean seed coating with a PGCit solution of 75% indicated that the seed quality and germination rate were not affected by the PGCit coating, concluding that this polymer is suitable for this application.

Struvite-based composites for slow-release fertilization: a case study in sand.

Struvite (St) recovered from wastewaters is a sustainable option for phosphorus (P) recovery and fertilization, whose solubility is low in water and high in environments characterized by a low pH, such as acidic soils. To broaden the use of struvite in the field, its application as granules is recommended, and thus the way of application should be optimized to control the solubility. In this study struvite slow-release fertilizers were designed by dispersing St particles (25, 50, and 75 wt%) in a biodegradable and hydrophilic matrix of thermoplastic starch (TPS). It was shown that, in citric acid solution (pH = 2), TPS promoted a steadier P-release from St compared to the pure St pattern. In a pH neutral sand, P-diffusion from St-TPS fertilizers was slower than from the positive control of triple superphosphate (TSP). Nevertheless, St-TPS featured comparable maize growth (i.e. plant height, leaf area, and biomass) and similar available P as TSP in sand after 42 days of cultivation. These results indicated that St-TPS slow P release could provide enough P for maize in sand, achieving a desirable agronomic efficiency while also reducing P runoff losses in highly permeable soils.

Zinc loading in urea-formaldehyde nanocomposites increases nitrogen and zinc micronutrient fertilization efficiencies in poor sand substrate.

Agricultural output needs significant increases to feed the growing population. Fertilizers are essential for plant production systems, with nitrogen (N) being the most limiting nutrient for plant growth. It is commonly supplied to crops as urea. Still, due to volatilization, up to 50 % of the total N application is lost. Slow or controlled release fertilizers are being developed to reduce these losses. The co-application of zinc (Zn) as a micronutrient can increase N absorption. Thus, we hypothesize that the controlled delivery of both nutrients (N and Zn) in an integrated system can improve uptake efficiency. Here we demonstrate an optimized fertilizer nanocomposite based on urea:urea-formaldehyde matrix loaded with ZnSO4 or ZnO. This nanocomposite effectively stimulates maize development, with consequent adequate N uptake, in an extreme condition - a very nutrient-poor sand substrate. Our results indicate that the Zn co-application is beneficial for plant development. However, there were advantages for ZnO due to its high Zn content. We discuss that the dispersion favors the Zn delivery as the nanoparticulated oxide in the matrix. Concerning maize development, we found that root morphology is altered in the presence of the fertilizer nanocomposite. Increased root length and surface area may improve soil nutrient uptake, potentially accompanied by increased root exudation of essential compounds for N release from the composite structure.

Co-fertilization of Sulfur and Struvite-Phosphorus in a Slow-Release Fertilizer Improves Soybean Cultivation.

In face of the alarming world population growth predictions and its threat to food security, the development of sustainable fertilizer alternatives is urgent. Moreover, fertilizer performance should be assessed not only in terms of yield but also in root system development, as it impacts soil fertility and crop productivity. Fertilizers containing a polysulfide matrix (PS) with dispersed struvite (St) were studied for S and P nutrition due to their controlled-release behavior. Soybean cultivation in a closed system with St/PS composites provided superior biomass compared to a reference of triple superphosphate (TSP) with ammonium sulfate (AS), with up to 3 and 10 times higher mass of shoots and roots, respectively. Root system architectural changes may explain these results, with a higher proliferation of second order lateral roots in response to struvite ongoing P delivery. The total root length was between 1,942 and 4,291 cm for plants under St/PS composites and only 982 cm with TSP/AS. While phosphorus uptake efficiency was similar in all fertilized treatments (11-14%), St/PS achieved a 22% sulfur uptake efficiency against only 8% from TSP/AS. Overall, the composites showed great potential as efficient slow-release fertilizers for enhanced soybean productivity.

Asbestos cement waste treatment through mechanochemical process with KH2PO4 for its utilization in soil pH correction and nutrient delivery.

The manufacture of asbestos materials has been banished worldwide due to their toxicity, but discarding the existing wastes remains a challenge. We investigated an alternative mechanochemical method to treat asbestos-cement materials by loading them with potassium and phosphorus from KH2PO4 during the milling process to obtain a product used as liming and soil conditioner. The results showed total asbestos fibrous elimination after 7 to 8 h of milling. The materials showed a slow-release fertilizer profile. The liming property is maintained when the asbestos-cement weight proportion used is equal to or higher than KH2PO4. A comparative soil experiment with limestone also indicates that lower doses of the K- and P-enriched detoxified asbestos cement were required to reach similar liming effects. Maize cultivation (greenhouse) was used to evaluate its performance showing higher biomass production for the sample loaded with potassium and phosphorous.

Different Zn loading in Urea-Formaldehyde influences the N controlled release by structure modification.

Nitrogen fertilization has been a critical factor for high crop productivity, where urea is currently the most used N source due to its high concentration and affordability. Nevertheless, urea fast solubilization leads to frequent losses and lower agronomic efficiency. The modification of urea structure by condensation with formaldehyde has been proposed to improve nutrient uptake by plants and to reduce environmental losses. Herein we show that the co-formulation with Zn strongly modifies the N release (in lab conditions) and, more important, the Zn source-ZnSO4 or ZnO-has a critical role. Urea-formaldehyde (UF) served as a matrix for the zinc sources, and chemical characterizations revealed that Zn particles influenced the length of the polymeric chain formation. Release tests in an aqueous medium showed that the UF matrix favors ZnO release and, on the other hand, delays ZnSO4 delivery. Soil incubation with the fertilizer composites proved the slow-release of N from UF, is ideal for optimizing nutritional efficiency. Our results indicated that the ZnO-UF system has beneficial effects for both nutrients, i.e., reduces N volatilization and increases Zn release.

Synergy of Aspergillus niger and Components in Biofertilizer Composites Increases the Availability of Nutrients to Plants.

Intensive fertilization has been required to provide nutrients for plant growth under the current agricultural practices being applied to meet the global food demands. Micronutrients such as zinc, manganese, and copper are required in small quantities when compared to macronutrients (such as nitrogen, phosphorus and potassium), but they are essential for the plant growth cycle and consequently for increasing productivity. Mineral oxides such as ZnO, MnO, and CuO are used in agriculture as micronutrient sources, but their low solubility limits practical applications in plant nutrition. Similarly, elemental sulfur (S0) can provide a high-concentration source of sulfate, but its availability is limited by the ability of the soil to promote S0 oxidation. We propose here the integration of these nutrients in a composite based on a biodegradable starch matrix containing mineral oxides and S0 in a dispersion that allowed encapsulation of the acidifying agent Aspergillus niger, a native soil fungus. This strategy effectively improved the final nutrient solubility, with the composite starch/S0/oxidemixture multi-nutrient fertilizer showing remarkable results for solubilization of the oxides, hence confirming a synergic effect of S0 oxidation and microbial solubilization. This composite exhibited an extended shelf life and soil-plant experiments with Italian ryegrass (Lolium multiflorum Lam.) confirmed high efficiencies for dry matter production, nutrient uptake, and recovery. These findings can contribute to the development of environmentally friendly fertilizers towards a more sustainable agriculture and could open up new applications for formulations containing poorly soluble oxide sources.

Role of urea and melamine as synergic co-plasticizers for starch composites for fertilizer application.

Herein we describe the interaction of starch, urea, and melamine (C3N6H6) in composite materials for use as controlled-release plant fertilizer. Slow-release fertilizers are important in minimizing nutrient losses due to run-off, leaching, and other factors. Urea is an effective plasticizer for starch and is an important nitrogen fertilizer throughout the world. Melamine also has high nitrogen content and could be combined with urea-starch composites to provide enhanced controlled-release fertilizer. This study reports the structural interaction and the performance gain of melamine addition to starch-urea composites. Composites were characterized by spectroscopic techniques (FT-Raman and 13C NMR) detailing the interaction between melamine, urea, and starch. These interactions helped facilitate extrusion processing by lowering viscosity and processing temperatures suggesting an enhanced starch plasticizing effect of starch-urea-melamine composites. Further research into the co-plasticization of starch by urea and melamine could be exploited for improved controlled-release fertilizer products. Further research into the co-plasticization of starch by urea and melamine could be exploited for improved controlled-release fertilizer products.

Role of Slow-Release Nanocomposite Fertilizers on Nitrogen and Phosphate Availability in Soil.

Developing efficient crop fertilization practices has become more and more important due to the ever-increasing global demand for food production. One approach to improving the efficiency of phosphate and urea fertilization is to improve their interaction through nanocomposites that are able to control the release of urea and P in the soil. Nanocomposites were produced from urea (Ur) or extruded thermoplastic starch/urea (TPSUr) blends as a matrix in which hydroxyapatite particles (Hap) were dispersed at ratios 50% and 20% Hap. Release tests and two incubation experiments were conducted in order to evaluate the role played by nanocomposites in controlling the availability of nitrogen and phosphate in the soil. Tests revealed an interaction between the fertilizer components and the morphological changes in the nanocomposites. TPSUr nanocomposites provided a controlled release of urea and increased the release of phosphorus from Hap in citric acid solution. The TPSUr nanocomposites also had lower NH3 volatilization compared to a control. The interaction resulting from dispersion of Hap within a urea matrix reduced the phosphorus adsorption and provided higher sustained P availability after 4 weeks of incubation in the soil.