Modeling spatiotemporal influences on the hydrothermal environment of the seedling recruitment microsite
Bullied, William John
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Modeling the seedling recruitment microsite involves characterization of the soil environment of the shallow profile from which weed seedlings recruit. Understanding the environment of the seedling recruitment microsite is the prelude to weed emergence studies. Because of spatial and temporal heterogeneity of the recruitment microsite, sufficient measurements are often not feasible. An experiment was established in 2003 and 2004 across topography within an annually cropped field in south-central Manitoba to determine the effect that hillslope aspect and position, and soil residue and depth would have on microsite environment within the shallow seedling recruitment zone. Microclimatic, topographic, soil surface and soil properties were assessed in the context of the weed recruitment microsite. The soil water retention characteristic was measured by pressure plate to determine water availability to germinating seeds at the various topographic positions. The soil water characteristic was evaluated across topography and soil depth. Evaluation of the soil water characteristic by pedotransfer function indicated that a single soil water characteristic is representative of the recruitment zone. Field and laboratory experimental measurements were used as parameterization for the simultaneous heat and water (SHAW) model to generate continuous water and temperature profiles for the recruitment zone. Soil temperature and temperature fluctuation decreased with depth in the recruitment zone. Despite differences of texture, bulk density, and organic matter across topography and soil depth, the soil water characteristic differed only across topography. Soil water potential fluctuated considerably at the soil surface due to numerous precipitation events and direct evaporation. Implications for germinating seeds is that the seedling recruitment zone is influenced by spatial effects of topography and the vertical location of the seed microsite. Physical process based modeling used in this study to predict temperature and water within the seedling recruitment zone enables better understanding of interactions between above-ground microclimate and the recruitment microsite. Such interactions enable linkage between atmospheric models and recruitment models that can enhance our ability to evaluate crop management decisions.