Simulation of Soil-Water Availability

Science Center Objects

How much water is stored in the soil?  Does agricultural management affect this?  Will this change if temperatures increase and plants need more water? 

In order to answer this question, we have focused on the differences in soil physical properties under four land management types (forest, pasture, traditional agriculture, and conservation agriculture) and whether these differences effect how water moves through the soil and how water remains in the soil to be available for plant use. 

 

Working with Natural Resource Conservation Service (NRCS) and University of Kentucky collaborators, IN-KY scientists are using hydrologic models that simulate soil-water storage as part of the water budget:

Ins = Outs

Precipitation + Irrigation = Evapotranspiration + Streamflow + Groundwater + Change in Storage

In these small basins, we are focusing on the how much water is used by plants (evapotranspiration) and how much ends up as streamflow; evapotranspiration is controlled by the solar radiation balance and is linked to temperature.  These basins are not irrigated, so precipitation (rain and snow) are the only “Ins” to the system and the relation to groundwater is expected to be constant.  This enables us to examine short-term (daily, monthly, seasonal) changes in storage of water in the soil. 

Our goal is to identify how land management might increase the soil water available for plants and how that can protect the ability to grow crops under higher temperatures and drought conditions.

This work builds on previous research that developed a hydrologic model that estimates water budget, including streamflow, actual evapotranspiration (plant water use), and soil-water storage – sometimes referred to as soil moisture.  The hydrologic model used was TOPMODEL (Beven and Kirkby, 1979) and our research showed the sensitivity of the water budget to the soil properties used to describe the environment. 

For the ongoing work, we are focusing on small areas of Indiana, Illinois, and Kentucky, in the NRCS Major Land Resource Area (MLRA) 120 and comparing laboratory and field measured data to simulations of how soil-water moves and is stored.  We are extending beyond our initial field sites by incorporating NRCS’s recent Rapid Assessment of U.S. Soil Carbon (RaCA), which provides differences in soil-physical properties among the different land management types. 

Installation of flume in small KY basin – this flume measures streamflow from a small basin, providing a better understanding of the water budget and allowing us to focus on soil-water storage. 

 

Installation of flume in small KY basin
Tom Ruby (USGS) and Brad Lee (University of Kentucky) install a flume in a small Kentucky basin

 

In addition to estimating soil-water storage, we need to understand how agricultural management, like conservation tillage and cover crops, change the ability of a soil to retain water for plant use.  Goals of conservation management include

  • increasing the amount of rain that infiltrates into the soil, instead of running off and eroding the soil,
  • increasing the amount of carbon stored in the soil, which helps bind the soil together and keep the soil moist. 

We have compared established methods to estimate hydrologic soil properties and developed some new methods in order to improve our ability to simulate soil-water storage.  This improves our ability to quantify how agricultural management effects soil-water availability for plants and how much management decisions improve the resiliencey of agriculture in times of drought and increased temperatures projected with climate change. 

 

 

 

 

Modeling Soil Water Storage

As we incorporate the estimated soil properties into our model, we will focus on

  • Quantifying the rate at which water moves through soil
  • Determining the space in which water can move at different conditions
  • Compare soil-water storage for recent (2001-2011) time periods to historical droughts like the 1960s and 2012. 
  • Evaluate simulated seasonal soil-water availability in terms of how much soil water is needed to sustain agricultural production of hay production, continuous corn, and a corn-soybean rotation. 
  • Use Global Climate Models (GCMs) to estimate how the temperature and precipitation projected for 2050 will affect soil-water storage and the ability to grow specific crops. 

Results from these simulations will be published as a journal article and as an extension bulletin for the agriculture community.