Figure 1.
The characteristics of the decomposition and zeta potential of rice straw.
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).
Figure 2.
The characteristics of the potassium release of rice straw.
The annotation in panel A indicates the homogeneity of variances (H) and ANOVA. The H-test was performed using the Levene test. *indicates significant differences at P<0.05. The values are the means of 3 replicates (±standard deviation). Means with the same letter are not significantly different. The insertion in panel B is the K release rate within 5 d.
Figure 3.
The adsorption of potassium by rice straw residues.
The dashed line shows the zero point in the panels. The values are the means of 3 replicates (±standard deviation).
Figure 4.
FT-IR spectra of natural dried rice straw and the rice straw residue at 110 d before and after potassium (K) adsorption.
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.
Figure 5.
The kinetics of water absorption for rice straw.
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).
Figure 6.
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.
Figure 7.
Schematic of the adsorption process of potassium (K+) on the rice straw residue surface.
(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.