Capillary Rise Studies in South Florida Soils
Anecdotal evidence from research conducted at the TREC has suggested that capillarity from our shallow groundwater table may contribute soil moisture to the root zone and provide some of the plant water needs (Al-Yahyai et al., 2003; Migliaccio et al., 2008).
ENVIROSCAN equipment installed to collect soil moisture at multiple depths.
Videos on YouTube
Project summary
Quantifying the relationship between groundwater table level and root zone soil water content in shallow groundwater conditions is important in South Florida due to the potential changes in groundwater level related to the Comprehensive Everglades Restoration Plan (CERP) and the resulting impacts these changes may have on deep rooted agriculture. The topic requires long and comprehensive research in multiple disciplines. This study represents a small contribution through three different objectives: soil water instrument calibration, methods of capillary rise interpretation and modeling the unsaturated zone of the soil profile. Results are intended to provide growers with science-based information on the benefits and challenges of the shallow groundwater table in this area.
Laboratory soil water characteristic curves helped to identify similarities in soil water retention patterns and low water holding capacity properties of gravel and limestone bedrock, attributing Krome soils water holding capacity to the loam fraction of the soil. Although gravel and limestone retention patterns were low, the soil water depletion was characterized to have very low volumetric water content changes in large increments of suction.
Onsite calibration of multi sensor capacitance probes using synchronized suction values from tensiometers as a reference to determine volumetric water content is a promising technique for conditions were standard calibration procedures are not possible. However limestone heterogeneity limited the results to an unpractical site specific calibration. Regression equations for instrument calibration in limestone bedrock conditions were characterized by their spatial and depth variability. As a result four regression models were proposed for calibration purposes. Relationships between Al-Yahyai et al. (2006) calibration regression model of Krome soils and
the proposed models were similar at equilibrium conditions, confirming the possibility to use a single calibration equation in Krome scarified and limestone bedrock.
Circular statistics represent a practical approach to interpret diurnal fluctuations of soil water content and groundwater level. Locations of statistically significant mean vectors were confirmed in all instruments and variables with Rayleigh test although many of the vectors were influenced by multimodal distributions attributed to multivariate effects. Mean vectors of soil water content at deeper depths were more related to mean vectors of groundwater; mean vectors of soil water content at shallower depths were more related to solar radiation and soil temperature. Circular-circular correlation analysis confirm in general a weak relationship between diurnal peaks of soil water content and the peaks found in groundwater and weather variables.
A hydrostatic model based on the drained to equilibrium principle was proposed to use groundwater level as a reference to predict soil water content. Predictions indicated this approach can be considered as a simple and useful reference of one-dimensional model technique. The proposed model was able to capture the general and most representative trends of soil water content changes in response to the shallow groundwater fluctuations although accuracy of predictions responded better at greater depths. Results have the potential to improve irrigation practices by considering groundwater contribution to the soil water status in the unsaturated zone.
Mr. Luis Barquin (MS graduate student in Agricultural and Biological Engineering) completed this project (Graduated Summer 2009).
Luis working on tempe cell experiment
Thesis Web link: Barquin Thesis
Publications: coming soon
Research poster: pdf