A New Method of Preparing Gel for DGT Technique and Application to the Soil Phosphorus Availability Test

ABSTRACT

There are different methods for soil phosphorus (P) availability assessment. Researchers have recently introduced a new method called diffusive gradients in thin films (DGT) to evaluate P availability in soils. The aim of this study was manufacturing DGT gel using copolymerization of acrylamide and allylic double bonds agarose to replace the patented agarose as a cross-linker. We evaluated the efficacy of the prepared gel and used the assembled DGT with that gel in 10 calcareous soils. We compared the available P measured with the assembled DGT in those soils to Olsen’s P measured in the same soils. Corn plant (Zea mays L.) was also grown in those soils in a greenhouse for two months. Results showed that the diffusion coefficient of P ions in the gel with 0.3% of allylagarose at 25 °C was 6.9 * 10^–6 cm².s⁻¹, implying that P ions were allowed to diffuse freely through the prepared diffusive gel. Measured P by the assembled DGT showed a close linear correlation (r² = 0.98) with the P concentrations measured in soil solutions extracted by the Olsen method. This demonstrates the prepared allylagarose cross-linked gels’ efficiency and thus the reliability of the assembled DGT in easily and rapidly measuring the soil’s available P. The P, as measured by the assembled DGT in the examined soils, indicated a little lower correlation coefficient (r = 0.77) than those measured by the Olsen method (r = 0.88). However, the CE values measured by DGT showed a good correlation with P uptake by the roots (r = 0.88, p ≤ 0.01). The best correlation between CE and P content in corn occurred for the measurements made after 48 h of DGT placement in soils. The 20-h measurements had about the same r value, indicating that 20 h is sufficient for the placement of DGT assembly in the soil before its removing and measuring the available P. According to our findings, acrylamide—allylagarose gel as a diffusive gel in DGT was found to be suitable for P measurements in both aqueous solutions and soil.

KEYWORDS:

• Corn
• cross-linker
• DGT
• Olsen-P

Acknowledgments

The corresponding author thanks the Lancaster University and Professor Hao Zhang for providing Standard DGT.

Funding

The corresponding author thanks the University of Tabriz for supplying the necessary expenses.

Additional information

Funding

The corresponding author thanks the University of Tabriz for supplying the necessary expenses.