State-space approach to analyze field-scale bromide leaching

Spatial variability of soil properties complicates the analysis of water and solute transport under field conditions. To meet this challenge, a novel experimental design with a scale-dependent treatment distribution was adopted earlier in a field study to assess the impact of land use and rainfall characteristics on Br^- leaching with the aid of spectral analysis. The objective of the current study was to identify the major underlying processes that controlled Br^- leaching in the previous experiment and to describe the spatial distribution of soil Br^- site-specifically and in different soil layers, using an autoregressive state-space approach. Based on the boundary conditions investigated in this study, the state-space models for Br^- concentration at 40-50 and 60-70cm exhibited the best prediction quality compared to those at other depths. As indicated by the weight of each variable, land use dominated the spatial pattern of Br^- at shallow depths; whereas, the spatial behavior of Br^- below 40cm was mainly affected by soil texture and to a smaller extent by rainfall intensity. In addition, the involvement of Br^- concentration and soil texture of the adjacent layer above in the state-space analysis helped to describe the spatial distribution of Br^- typically in the soil layer below 60cm. These results not only demonstrated the applicability of state-space technique in diagnosing spatial solute transport relationships; but also held important implications for the surface application of chemicals.