A proposed method for determining soil phosphorus desorption quantity–intensity relationships using anion-exchange membrane disks

Abstract

Resin extraction is considered a superior assessment of nutrient availability compared to chemical based soil tests. Information on phosphorus (P) desorption quantity–intensity (Q/I) relationships in soil is useful for environmental evaluations and for study of P movement. The objectives of this study were to develop method for measuring P desorption Q/I relationships using anion-exchange membrane disks (AEMD) and to compare this proposed method with the commonly accepted method using anion-exchange resin bead bags (AERBB). Five soil series from South Dakota (Barnes, Egan, Egeland, Glenham, and Maddock) were used. The soil samples were enriched with various concentrations of P and incubated at field capacity for 2 weeks. Phosphorus enriched subsamples were equilibrated with bicarbonate-saturated AEMD or AERBB for 72 h. The quantity factor (Q) was taken to be represented by either AEMD extractable P or AERBB extractable P. The intensity factor (I) was determined by measuring solution P after equilibration with AEMD or AERBB. The AEMD extractable P was nearly 80% of the amount of AERBB extractable P even though the exchange capacity of the AEMD was approximately 20% of the AERBB's exchange capacity. The AEMD extractable P was significantly correlated to the AERBB extractable P in all of the soils investigated.

The anion-exchange membrane (AEM) behaved in a similar manner to the anion-exchange resin (AER). The observed Q/I data for both methods could be described using the equations or Both equations generated similar curves and estimates of buffering power The equation was evaluated, but it did not describe the P desorption Q/I data well for either method. The AEM behaved in a similar manner to the AER, however large volumes of resin beads in well stuffed bags appeared to restrict the equilibration of the soil–water–AERBB system and tended to trap soil particles. These types of problem were minimal in the AEMD method because the disk chains are much smaller in size and easily washed clean with a squirt bottle. The highest number of AEM disks used per set for this study was not enough to clearly determine Q _max of P, whereas the AERBB method required bags with smaller amounts of AER beads per bag to describe better Q/I curves. The values tended to be associated with soil texture, exchangeable Fe, and available P in soils.

Acknowledgments