Estimation of retention curves for sandy soils and their impact on water transport in SVAT models
Olivia Williams
The movement of water in soil has broad impacts on micrometeorology. The exchange of heat and
moisture between the atmosphere and the earth’s surface moderates the microclimate, making it
habitable for organisms. Water flow, air flow, evaporation, heat flux and radiation flux are all
interrelated processes between air and soil, which affect local climate and vegetation. Soil Vegetation
Atmosphere Transfer (SVAT) models have incorporated these processes as part of larger Global Climate
Models (GCMs), which show broad atmospheric circulation patterns. SVAT models focus on the land
surface and its exchange with the local atmosphere. Water is one of the most important components of
the model, regulating heat and radiation fluxes.
Water flows in soil according to its potential energy, which is determined by its location and the
properties of the soil. Sandy soil has large, coarse particles with large pores in between. These large
pores allow sandy soil to absorb water more quickly than clayey soil, but they also allow water to more
quickly evaporate due to the ways in which water and the soil particles attract each other, called matric
potential. Matric potential results from capillary and adsorptive forces which bind water to soil particles
and lower the overall potential of the water. Water flows from areas of high potential to low,
attempting to find equilibrium. The amount of water which remains in the soil at equilibrium is a
function of matric potential represented by the water retention curve. There is no universal theory for
predicting a water retention curve for a given soil type, but there are many equations which can
estimate the curve for specific conditions. The van Genuchten and Brooks-Corey approaches are the
most widely used.
The objectives of this project are to determine the soil properties at the location of interest in order to
estimate water retention curves using the van Genuchten and Brooks-Corey equations, and to input
these curves into an SVAT model to see the effects.
The study site is at the UF/IFAS Plant Science Research & Education Unit in Citra, FL, in the sandy soil of a
corn field. Two locations in the field will be sampled at various depths, ultimately at least to one meter,
since the top meter of soil is the most important for plant growth. These samples will be analyzed in the
Soil Moisture Laboratory, by saturating the soil with water and applying pressure to the sample. Other
soil samples will be taken simultaneously to understand the soil texture and composition (with
measurements of porosity, and content of organic matter, sand, silt, and clay). The data from these
analyses will be used to estimate water retention curves which can be put into the Land Surface Process
Model, a type of SVAT, to understand water movement in the particular soil found at the research field.
Timeline:
June 20-24
-Locate soil sample rings and weigh them to a hundredth of a gram
-Understand old charts of data
-By June 24, have samples for bulk density/partial moisture curve ready for
Kelley
June 27-July 1
-Have Fortran and LSP installed on Zelda
-Finish taking all soil samples and make appointment with Kelley for textures
-by June 28, have samples for moisture curve ready for Kelley. Go to lab and see
process of soil moisture test
C-ode water retention equations in Matlab
July 4-8
-Practice with models in Fortran and Matlab
-by July 8, have working knowledge of how to use models and input variables
July 8-12
[Florida Waters Tour]
July 13-15
-Receive soil data from labs
-Input data into models
July 18-22
-Input all available good data into models and have them adjusted and working
as desired
July 25-29
-Finish project and presentation for ABE dept