title: Application of the diffusive gradients in thin films technique for available potassium measurement in agricultural soils: effects of competing cations on potassium uptake by the resin gel.
abstract: The utilization of Amberlite (IRP-69 ion-exchange resin, 100-500 wet mesh) as the binding phase in the diffusive gradients in thin films (DGT) technique has shown potential to improve the assessment of plant-available K in soils. The binding phase has recently been optimized by using a mixed Amberlite and ferrihydrite (MAF) gel which results in linear K uptake over extended deployment periods and in solutions with higher K concentrations. As restriction of K uptake by Ca on the Amberlite based resin gel has been previously proposed, potential competing effects of Ca(2+), Mg(2+) and NH(4+) on K uptake by the MAF gel were investigated. These cations had no effect on K elution efficiency which was 85%. However, K uptake by the MAF gel was restricted in the presence of competing cations in solution. Consequently, the diffusion coefficient of K decreased in the presence of cations compared to previous studies but was stable at 1.12×10(-5)cm(2)s(-1) at 25°C regardless of cation concentrations. Uptake of K by the DGT device was affected by the presence of excessive Ca in more than 30% of twenty typical Australian agricultural soils. However, this problem could be circumvented by using a shorter deployment time than the normal 24 h. Moderate correlation of concentrations of K extracted by DGT with Colwell K (extracted by NaHCO(3), R(2)=0.69) and NH4OAc K (R(2)=0.61) indicates that DGT measures a different pool of K in soils than that measured by the standard extractants used. In addition, the MAF gel has the ability to measure Ca and Mg simultaneously.
authors.affiliation: School of Agriculture, Food and Wine, University of Adelaide, SA 5064, Australia. Electronic address: yulinzhangbest@126.com.
authors.forename: Yulin
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Agriculture, Food and Wine, University of Adelaide, SA 5064, Australia.
authors.forename: Sean
authors.initials: S
authors.lastname: Mason
authors.affiliation: School of Agriculture, Food and Wine, University of Adelaide, SA 5064, Australia.
authors.forename: Ann
authors.initials: A
authors.lastname: McNeill
authors.affiliation: School of Agriculture, Food and Wine, University of Adelaide, SA 5064, Australia; CSIRO Sustainable Agriculture Flagship, CSIRO Land and Water, PMB 2, Glen Osmond, SA 5064, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McLaughlin
mesh_terms: D000383:Agriculture; D002118:Calcium / Q000032:analysis; D002412:Cations / Q000032:analysis; D004058:Diffusion; D004784:Environmental Monitoring; D005290:Ferric Compounds / Q000737:chemistry; D008274:Magnesium / Q000032:analysis; D011188:Potassium / Q000032:analysis*; D012117:Resins, Synthetic / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*
chemical_list: D002412:Cations; D005290:Ferric Compounds; D012117:Resins, Synthetic; D012987:Soil; C092844:ferric oxyhydroxide; C046797:amberlite; D008274:Magnesium; D011188:Potassium; D002118:Calcium
keywords: Calcium; Deployment time; Diffusion; Diffusive gradients in thin films; Magnesium; Potassium; Soil testing