State-Space Models Describe the Spatial Variability of Bromide Leaching Controlled by Land Use, Irrigation, and Pedologic Characteristics

Understanding leaching mechanisms of surface-applied solutes and pesticides is of paramount interest. One problem inherent in leaching experiments at the field scale is the considerably large spatial variability of flow-controlling soil properties. Analyzing treatment effects based on the mean and variance of randomly taken field observations can become obsolete if there is a huge inherent variance in the set of measurements. Therefore, in a new experimental design, presented earlier and with treatments being arranged in a scale-dependent manner, Bromide (Br-) leaching was analyzed under two contrasting land uses (cropland vs. grassland) and affected by different irrigation characteristics. Given the cyclic arrangement of treatments and pedologic properties such as texture and bulk density, the Br- leaching process and changes in the soil water status during the experiment were described by autoregressive state-space models. The results showed that changes in soil water status could be described by state equations comprising the irrigation amount and to a smaller extent the land use. The spatial process of Br-leaching was described by autoregressive state-space models incorporating land use, irrigation amount, and changes in the soil water status during the experiment, as well as clay content and bulk density as means of the analyzed profiles. The results of this study demonstrated the efficiency of state-space models for describing field solute transport based on experimental treatments and underlying pedological properties. This way of analysis improved our knowledge about the relative influence of these factors on field-scale solute leaching.