Using diffusive gradients in thin films technique for in-situ measurement of labile phosphorus around Oryza sativa L. roots in flooded paddy soils

ABSTRACT

Behavior of phosphorus (P) in flooded rice soil is controlled by iron (Fe) redox cycling in root-zone. In this study, we applied a novel approach—the diffusive gradients in thin films (DGT) technique—for investigating the in-situ distribution of labile phosphorus (P) and Fe in close proximity to Asian rice (Oryza sativa L.) roots at submillimeter to millimeter spatial resolutions during the seedling and booting stages. We conducted a seven-year field experiment under rice-wheat rotation with different P fertilizer treatments. The results showed a significant and strong positive relationship of the average DGT-labile P concentration with soil Olsen P (R² = 0.77, P < 0.01) and with rice total P concentration (R² = 0.62, P < 0.05). Furthermore, results on one- and two-dimensional changes of DGT-labile P indicated that fertilization only in the wheat season produced sufficient amounts of labile P in the flooded paddy soils, similar to when fertilizer was applied only in the rice season; dissolved P concentrations, however, were lower. A co-occurrence and significant positive correlation (P < 0.01) between DGT-labile P and Fe indicated Fe-coupled mobilization of P in flooded paddy soils. These results collectively indicated that the DGT technique provided information on in-situ distribution of labile P and its variability in close proximity to rice roots. This suggests that the DGT technique can improve our understanding of in-situ and high-resolution labile P processes in paddy soils and can provide useful information for optimizing P fertilization.