State-space approach to analyze field-scale bromide leaching

• State-space approach detected spatial associations of Br− in different layers.
• State-space models revealed different flow regimes in the soil profile.
• Land use dominated the spatial distribution of soil Br− at shallow depths.
• Soil texture was the major factor controlling spatial Br− patterns below 40 cm.
• Involving Br− and texture of the layer above improved description of Br− below 60 cm.

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 60–70 cm 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 40 cm 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 60 cm. 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.