Dynamics of Potassium Release and Adsorption on Rice Straw Residue

<div><p>Straw application can not only increase crop yields, improve soil structure and enrich soil fertility, but can also enhance water and nutrient retention. The aim of this study was to ascertain the relationships between straw decomposition and the release-adsorption processes of K⁺. This study increases the understanding of the roles played by agricultural crop residues in the soil environment, informs more effective straw recycling and provides a method for reducing potassium loss. The influence of straw decomposition on the K⁺ release rate in paddy soil under flooded condition was studied using incubation experiments, which indicated the decomposition process of rice straw could be divided into two main stages: (a) a rapid decomposition stage from 0 to 60 d and (b) a slow decomposition stage from 60 to 110 d. However, the characteristics of the straw potassium release were different from those of the overall straw decomposition, as 90% of total K was released by the third day of the study. The batches of the K sorption experiments showed that crop residues could adsorb K⁺ from the ambient environment, which was subject to decomposition periods and extra K⁺ concentration. In addition, a number of materials or binding sites were observed on straw residues using IR analysis, indicating possible coupling sites for K⁺ ions. The aqueous solution experiments indicated that raw straw could absorb water at 3.88 g g⁻¹, and this rate rose to its maximum 15 d after incubation. All of the experiments demonstrated that crop residues could absorb large amount of aqueous solution to preserve K⁺ indirectly during the initial decomposition period. These crop residues could also directly adsorb K⁺ via physical and chemical adsorption in the later period, allowing part of this K⁺ to be absorbed by plants for the next growing season.</p></div

SEM micrographs of the rice straw residue surface on different days after incubation: A 0 d, B 15 d, C 60 d and D 110 d.

<p>SEM micrographs of the rice straw residue surface on different days after incubation: A 0 d, B 15 d, C 60 d and D 110 d.</p

Schematic of the adsorption process of potassium (K⁺) on the rice straw residue surface.

<p>(a) K⁺ retained on the straw in the form of an aqueous solution absorbed by residue; (b) K⁺ adsorbed via electrostatic interaction; and (c) K⁺ fixed on the residue surface by chemically interfacial adsorption. The size of the three letters indicates the amount of K⁺ reserved on the residue by the corresponding process.</p

The characteristics of the decomposition and zeta potential of rice straw.

<p>The annotations in the panels indicate the homogeneity of variances (H) and ANOVA for the remaining dry matter and zeta potential. The H-test was performed using the Levene test. **indicates significant differences at P<0.01. The values are the means of 3 replicates (±standard deviation).</p

FT-IR spectra of natural dried rice straw and the rice straw residue at 110 d before and after potassium (K) adsorption.

<p>Solid line A represents the infrared spectrum of natural dried rice straw. Solid lines B and C represent the infrared spectra of the rice straw at 110⁻¹ KCl solution, respectively. The data in the panel are the peak wavenumbers.</p

The adsorption of potassium by rice straw residues.

<p>The dashed line shows the zero point in the panels. The values are the means of 3 replicates (±standard deviation).</p

The kinetics of water absorption for rice straw.

<p>Panel A shows the changes of water absorption in dried rice straw. Panel B shows the changes of water absorption of straw residue for different decomposition periods. The values are the means of 3 replicates (±standard deviation).</p

Solar Cell with Photocatalyst Layers on Both the Anode and Cathode Providing an Electromotive Force of Two Volts per Cell

Solar cells and fuel cells are essential devices that convert sustainable energy into electricity. However, the electromotive forces they provide are in principle limited to less than 1 V, and consequently, they need to be connected in series for practical use. In this study, photocatalyst layers with thicknesses of 0.8–2.1 μm were applied to both electrodes. The primary particle size of TiO₂ was optimized (15–21 nm), and its performance was further improved by doping with organic dyes, e.g., anthocyanins. The electron conductivity of TiO₂ was found to be a primary factor in the performance of the cells, but the film flatness also reduced resistance and improved cell performance. Interestingly, the efficiency of TiO₂ could be evaluated based on the exchangeable surface O atoms via its ¹⁸O₂ exchange tests to suppress the reverse reaction step in water photo-oxidation, which occurs on the anode. UV and visible light were absorbed by TiO₂ and the organic dyes, respectively, creating an electron flow path from the valence band to the conduction band of TiO₂, then, the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) of the organic dyes, then the anode, and finally the cathode via the external circuit. The flow of electrons and holes (separated from electrons in BiOCl on the cathode by UV–visible light) enabled a <i>V</i>_OC value of 2.11 V and maximum power of 73.1 μW cm^–2

Factors of major adverse cardiac events (MACEs) and relative risk by quartiles of serum Mg level.

<p>PCI, percutaneous coronary intervention; 95% CI, 95% confidence interval.</p><p>*<i>P</i><0.05.</p><p># adjusted for positive family history, smoking status, hypertension, hypercholesterolemia, and diabetes at baseline.</p

Relative risk by quartiles of serum Mg level according to different clinical presentation.

<p>95% CI, 95% confidence interval.</p><p>*<i>P</i><0.05, **<i>P</i><0.01.</p><p># adjusted for age, positive family history, smoking status, hypertension, hypercholesterolemia, and diabetes at baseline.</p