Phosphorus speciation by P-XANES in an Oxisol under long-term no-till cultivation
João Arthur Antonângelo, Ruan Francisco Firmano, Hailin Zhang, Marina Colzato, Dalton Belchior Abdala, Hudson Wallace Pereira de Carvalho, Adílson de Oliveira, Luís Reynaldo Ferracciú Alleoni
Abstract
In highly weathered soils with low phosphorus (P) content and high P fixing capacity, long-term application of P fertilizers may influence P speciation. The combined use of macro- and microscopic techniques can provide information on P distribution and reactivity in soils, which is an important key to determine its loss potential into the environment. In this study, we aimed to evaluate the effects of rates of P on solid-state P speciation in an Oxisol under no-till (NT) for 26 years in Brazil. Soil samples were collected from experimental plots that received 0 to 50 kg ha−1P annually. X-ray Fluorescence microanalysis (µ-XRF), X-ray Absorption Near-Edge Structure (XANES), and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopies were used along with soil mineralogical and conventional chemical analyses. Phosphorus availability increased with the applied P rates. Based on the µ-XRF analysis, high Pearson correlation coefficients (r) were obtained for P vs Al, Si and Fe contents (r = 0.97, 0.81 and 0.84, respectively, with P < 0.0001); and partial correlation showed co-localized effects mainly for Al and Si. The Fe-EXAFS results hinted to the presence of non-crystalline iron (Fe) minerals being favored in the cultivated soils, likely as a consequence of the higher rates of P applied and utilization by the crops. P-XANES data revealed that after the fertilization, the proportion of P sorbed to goethite did not vary, but the proportion of P sorbed to hematite decreased, while P sorbed to kaolinite increased. The long-term continuous application of P fertilizers beyond plant uptake capacity favored P build-up in soils, resulting not only in poor P use efficiency but also in exacerbated risk of P loss to the environment.