Effects of Shaking Time on Long‐term Phosphorus Desorption using Dialysis Membrane Tubes filled with Hydrous Iron Oxide

Abstract

The use of dialysis membrane tubes filled with hydrous ferric oxide (DMT‐HFO) solution has recently been reported as an effective way to characterize phosphorus (P) desorption over a long term in laboratory studies. However, the DMT‐HFO method, similar to other soil tests, exploits 100% of the sample volume, which is much more than what the plant roots can exploit under natural conditions. One possible solution to mimic the root P uptake better by this method could be to modify the shaking procedure using different shaking periods. The objectives of this study were to investigate the influence of variable shaking times on the rate of P desorbed by the DMT‐HFO method and to relate the desorption indices generated with maize yield in a diferential P fertilizer trial. The effect of varying shaking options on the extractable DMT‐HFO‐Pi for the different P treatments showed a significant difference only for treatment MNPK. Significant correlations were obtained between the labile pool rate coefficients [kA1 (0.92**), kA2 (0.99**), kA3 (0.92**), and kA4 (0.92**)] and maize grain yield for shaking options 1, 2, 3, and 4, respectively. The only rate coefficient from the less labile pool, kB, which showed a significant but moderate correlation (r = 0.78*) with maize grain yield, was kB1. The cumulative amount of P (mg kg−1) extracted by DMT‐HFO showed no statistically significant correlations with maize grain yield in all the options considered. Judging from the r values, the rate coefficients appeared to be better indices of plant availability than the amount of P extracted by DMT‐HFO, and based on the r values, option 2 seemed relatively better than the others because it showed the strongest correlation in both cases.