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Arid and semiarid soils of southern Iran may fix a large content of applied potassium (K), but the fixed K may be gradually supplied to plants. Sixteen representative soils under orange cultivation (Citrus sinensis (L.) Osbeck) from arid and semiarid regions of southern Iran were selected and K fixation capacity of the soils were calculated. Then, the K-treated and control soil samples were extracted for K during 10 stages with 0.01 M CaCl2. Results indicated that the studied soils were able to fix 25 to 280 mg K kg–1. Mean contents of cumulative K released ranged 48–262 and 8–512 mg kg–1 for the control and K-treated soils, respectively, with significant difference (p < 0.05). The control soils released 42–69% (mean of 57%) of K during the first three stages of extraction, and this was significantly (p < 0.05) lower than that for the K-treated soils (55–86% with mean of 69%). No significant difference was found between the control and K-treated soils in K release during 4 to 10 stages of extraction. The fixation of added K is occurred in more available sites (wedge zone) of clay minerals and the fixed K may be released easily during the K extraction experiment. Thus, the availability of the fixed K (originated from chemical fertilizers) is considerably more than the native non-exchangeable K ions due to its fixation in the mineral edges. Generally, calcareous soils in arid environments had a high proportion of K-bearing minerals and able to fix added K fertilizers, but the fixed K may be released easily during the plant growth season and it should be considered as a benefit process. [ABSTRACT FROM AUTHOR]

Chitosan is a cationic natural polymer which has been widely used in various areas. Present study focused on the preparation of the chitosan nanoparticles (NPs) throughout ionic gelation method and using tripolyphosphate (TPP), as non-toxic polyanion counter-ions. Chitosan NPs solutions were prepared by mixing of the 10 mL chitosan solutions, with different concentrations (1, 2 and 3 mg/mL), and different amounts of the TPP (4, 6, 8, 10, 12, 14 mL) at 35 °C. Physico-chemical characteristics of prepared chitosan NPs solutions were evaluated using FT-IR, DLS, TEM and UV-Vis spectroscopy. Achieved results indicated that optimum conditions to prepare opalescent chitosan NPs suspension achieved by using 10 mL of chitosan solution (3 mg/mL) and 14 mL TPP. The provided chitosan NPs at these conditions had highest turbidity (0.317 a.u.) and zeta potential (+15.9 mV) values. The formed spherical chitosan NPs in the solution had minimum mean particle size of 20 nm. Antibacterial activities analysis against both Gram positive and negative bacteria strains indicated that the formed chitosan NPs had higher bactericidal effects as compared to the chitosan solution. Obtained results also revealed that both chitosan solution (3 mg/mL) and its prepared NPs had strong fungicidal activity against Aspergillus flavus. [ABSTRACT FROM AUTHOR]