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Long‐term effects of rice (Oryza sativa L.) cultivation with varying nutrient management on soil P fraction are important to understand from soil nutritional and environmental point of view. Soil P fractionation gives an idea about the soil P supplying capacity to plants. The present experiment was conducted to evaluate the effect of different nutrient management in wetland rice on the changes of soil P fraction at different depths. Soil samples from five depths (0–5, 5–10, 10–15, 15–30, and 30–50 cm) were collected from a long‐term experimental field classified as a Chhiata clay loam, hyperthermic Vertic Endoaquept. The field received six treatments for 10 yr: absolute control with no fertilizer applied (T1), one‐third of recommended fertilizer doses (T2), two‐thirds of recommended fertilizer doses (T3), full doses of recommended fertilizers (T4), T2 + 5 Mg cow dung (CD) and 2.5 Mg ash ha−1 (T5), and T3 + 5 Mg CD and 2.5 Mg ash ha−1 (T6). The apparent balance of P compared with the initial P status after 10 yr varied from −115 kg ha−1 under T1 to 348 kg ha−1 under T6 The P fractionation study was conducted over the treatments and soil depth. Treatment and depth had no significant effect on solution P. Larger concentrations of NaHCO3 soluble P, NaOH extracted inorganic P (Pi), and acid P were observed under treatments with organic fertilizers (T5 and T6) than with other treatments at 0‐ to 5‐, 5‐ to 10‐, and 10‐ to 15‐cm depths. The concentrations of NaHCO3–P, NaOH‐Pi and acid P fractions were lowest under T1 and T2 treatments. At 15 to 30 cm or lower soil depths, none of the P fractions were affected by treatments. The change in NaOH organic P (Po) and residual P (extracted with HNO3 + HClO4) with soil depth was not significant, and the differences in these P fractions under the tested P treatments were not large. The depletion of NaHCO3–P and NaOH‐Pi at the 0‐ to 15‐cm depth under control and T2 suggests that the rice plant depends upon these fractions of P. The P depletion profile in wetland rice appears to be confined within the first 15‐cm depth. The mean P uptake by rice showed a polynomial relationship with NaHCO3–P and NaOH‐Pi (average of 0–15 cm) and it was linearly correlated with acid P (0–15 cm).

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A novel solid-phase extractant was synthesized by coupling graphene oxide (GO) on chloromethylated polystyrene through an ethylenediamine spacer unit to develop a column method for the preconcentration/separation of lead prior to its determination by flame atomic absorption spectrometry. It was characterized by Fourier transform infrared spectroscopy, far-infrared spectroscopy, thermogravimetric analysis/differential thermal analysis, scanning electron microscopy, energy-dispersive spectrometry, and transmission electron microscopy. The abundant oxygen-containing surface functional groups form a strong complex with lead, resulting in higher sorption capacity (227.92 mg g(-1)) than other nanosorbents used for sorption studies of the column method. Using the column procedure here is an alternative to the direct use of GO, which restricts irreversible aggregation of GO and its escape into the ecosystem, making it an environmentally sustainable method. The column method was optimized by varying experimental variables such as pH, flow rate for sorption/desorption, and elution condition and was observed to exhibit a high preconcentration factor (400) with a low preconcentration limit (2.5 ppb) and a high degree of tolerance for matrix ions. The accuracy of the proposed method was verified by determining the Pb content in the standard reference materials and by recovery experiments. The method showed good precision with a relative standard deviation <5%. The proposed method was successfully applied for the determination of lead in tap water, electroplating wastewater, river water, and food samples after preconcentration.

In this work, a hydrophilic sandwich-like graphene oxide (GO) ion-imprinted polymer (IIP) was synthesized via the surface imprinting technique to develop a dispersive magnetic solid-phase extraction method for the preconcentration of Ni(II) by flame atomic absorption spectrometry (FAAS). In this imprinted polymer, allyl-rich amines (monomer) and ethylene glycol dimethacrylate (EGDMA) (cross-linker) act as platforms for Ni(II) recognition. Most importantly, the influence of other transition metals as well as alkali/alkaline earth metals in the samples was evaluated to compare the imprinting effect between IIP and nonimprinted polymer (NIP) as a control. The IIP for Ni(II) in a binary mixture provides >99% recovery with a good selectivity coefficient, whereas NIP could not recognize a specific metal ion from competitive ions due to the absence of imprinting effect. Moreover, the introduced specific binding sites with complementary shapes and sizes for Ni(II) recognition in IIP exhibited high adsorption capacity as compared to NIP and fast chemical kinetics with a pseudo-second-order model. The ease of separation from aqueous solutions by an external magnet is facilitated due to embedded Fe 3 O 4 nanoparticles. By utilizing nonlinearized isotherm modeling, two-parameter models (Langmuir, Freundlich, and Dubinin−Radushkevich) and three-parameter models (Redlich− Peterson and Sips) were analyzed with error analysis (reduced χ 2 , residual root-mean-square error (RMSE), and sum squares error (SSE)). Additionally, the structural modifications of GO were examined by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and atomic force microscopy (AFM). No significant difference was found in FTIR spectra of IIP and NIP. Accuracy was presented by SRM and recovery studies. The synthesized sorbent possesses high recognition ability even after seven regeneration cycles, illustrating potential applications for Ni(II) determination in various food and water samples.