Unit Four – Plant-Soil-Water Relationship
What is the plant-soil-water relationship and why does it matter?
The relationships of plant, soil and water systems is one of interdependence. In the context of water quality and conservation:
- Plant health is important in several ways: 1) for nutrient uptake and 2) for vegetative cover to minimize the effects of rainfall energy and potential erosion. Both impact the potential transport of sediment and any adsorbed nutrients/pesticides into water.
- Soil health determines permeability, water infiltration rates, water-holding capacity, nutrient-holding capacity, plant health support, and the existence of and types of soil fauna.
- Water in sufficient quantities will promote plant and soil life processes. In excessive quantities, it has the potential to deprive both plants and soil fauna of oxygen, impairing their life processes and health. Quantities of water in excess of holding capacity have the potential to transport sediment, nutrients and pesticides.
Human intervention in these systems can be either helpful or disruptive.
This unit assumes that the Advanced Master Gardener has a thorough understanding of the following underlying concepts:
- Basic soil science
- Plant growth and the nutrient needs of plants
- The hydrologic cycle
- Nutrient movement in soil and factors effecting nutrient availability to plants
Soil Conditions Affecting Soil Health, Plant Health and the Potential for Runoff
Natural processes affect soils and the plants that soils support, but it is disturbed soils that present significant opportunities to the Advanced Master Gardener for programming. Contending with or returning disturbed soils to a condition that supports plant growth and minimizes runoff and leaching is a challenge.
The soils in many home landscapes have been disturbed through the construction process, leaving little that resembles native soil. However, knowing the characteristics of the soils in Virginia’s major soil divisions and physiographic regions may help with the understanding of dominant geological factors influencing the formation of soil and the types of vegetation they support. The Advanced Master Gardener – Water Program Manager must also understand how disturbed soils affect plants and soil fauna and how to improve those conditions.
Virginia Department of Conservation and Recreation. 2013. “The Natural Communities of Virginia, Classification of Ecological Community Groups: Overview of the Physiography and Vegetation of Virginia.” Accessed October 29, 2014. http://www.dcr.virginia.gov/natural_heritage/natural_communities/ncoverview.shtml.
Baker, James C. 2009. “Soils of Virginia.” In Agronomy Handbook. Virginia Cooperative Extension Publication 424-100, 69-74. Public domain. Accessed October 29, 2014. http://pubs.ext.vt.edu/424/424-100/424-100_pdf.pdf.
Fine, Aubrey. 2010. “The Price Paid for Building Anew.” Artifacts: A Journal of Undergraduate Writing, 5. The University of Missouri. Accessed December 9, 2014. https://artifactsjournal.missouri.edu/2010/05/155/.
Daniels, W. Lee. 2011. “Managing Urban Soils.” In Urban Nutrient Management Handbook. Blacksburg, Virginia: Virginia Cooperative Extension, 3-1 – 3-7, 3-10 – 3-13. Accessed November 11, 2014. http://www.hort.vt.edu/Documents/FoxUrbNutMgmt.pdf.
Elmendorf, Bill. 2008. “Understanding Tree Planting in Construction-Damaged Soils.” Penn State Cooperative Extension, 6-13. Accessed December 9, 2014. http://pubs.cas.psu.edu/FreePubs/pdfs/uh187.pdf.
Bainbridge, David. No date. “The effects of disturbance on soil characteristics relevant for revegetation.” San Diego State University, Soil Ecology and Restoration Group. Accessed December 9, 2014. http://www.sci.sdsu.edu/SERG/techniques/disturbance.html.
Water Infiltration Factors and Potential for Runoff
Because one concern is water leaving a property potentially transporting sediment, nutrients and/or pesticides, the Advanced Master Gardener managing water programs must understand the energy in rainfall and how that may result in pollutant transport. This is more likely at certain times of year, in locations of higher rainfall or on properties with specific soil characteristics. Soil characteristics will also determine amounts of rainfall that enter the soil surface.
“Characteristics of Rainfall.” 2010. Northeast Region Certified Crop Advisor Study Resources, Cornell University. Accessed December 5, 2014. http://nrcca.cals.cornell.edu/soil/CA2/CA0210.php.
“Historical Climate Summaries for Virginia.” 2007. Southeast Regional Climate Center, University of North Carolina at Chapel Hill. Accessed December 9, 2014. http://www.sercc.com/climateinfo/historical/historical_va.html.
“What is rain splash erosion and why is it important?” No date. Exploration: Vanderbilt’s Online Research Magazine. Accessed December 9, 2014. http://www.vanderbilt.edu/exploration/text/index.php?action=view_section&id=1104&story_id=268&images.
“Soil Infiltration.” 2010. Northeast Region Certified Crop Advisor Study Resources, Cornell University. Accessed December 5, 2014. http://nrcca.cals.cornell.edu/soil/CA2/CA0211.1.php.
“Runoff.” 2010. Northeast Region Certified Crop Advisor Study Resources, Cornell University. Accessed December 5, 2014. http://nrcca.cals.cornell.edu/soil/CA2/CA0211.4.php.
Plant Growth and Soils
Soils characteristics determine how water, oxygen and gases pass through soils, and will physically limit or facilitate root growth. In addition to climate conditions, the stage of plant growth, the depth at which different plants extract water, and other factors define the amount of water withdrawn and the amount of energy a plant must expend. When there is an excess of nutrients without moisture or the plant is unable to take up nutrients, the result may be runoff, leaching or stress – even death – to the plant.
“Permeability and Infiltrability.” 2010. Northeast Region Certified Crop Advisor Study Resources, Cornell University. Accessed December 5, 2014. http://nrcca.cals.cornell.edu/soil/CA2/CA0213.php.
“The Effect of Soil Saturation on Trees and Other Plants.” No date. University of Florida, Hillsborough County Extension Service. Accessed December 9, 2014. http://hillsborough.ifas.ufl.edu/prohort/files/pdf/publications/HC-SoilSaturation.pdf.
Niemiera, Alex X. 2009. “Diagnosing Plant Problems.” Virginia Cooperative Extension Publication 426-714. Public domain. Accessed December 9, 2014. http://pubs.ext.vt.edu/426/426-714/426-714.html.
Water Holding Capacity
Once water infiltrates the soil surface, the soil must then perform the function of holding water for use by plants. Knowing the soil characteristics that affect water holding capacity will help the Water Program Manager assist homeowners with soil improvement, plant selection and maintenance. Soil surveys contain the needed information for field capacity and permanent wilting point. Perhaps the most important factor.
Rogers, Danny H. and William M. Sothers. 1996. “Soil, Water and Plant Relationships.” Manhattan, Kansas: Cooperative Extension Service. Reprinted with permission. Accessed October 17, 2014. http://irrigationtoolbox.com/ReferenceDocuments/Extension/Kansas/l904.pdf.
National Cooperative Soil Survey. 2013. U.S. Department of Agriculture, Natural Resources Conservation Service. Accessed December 9, 2014. http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm.
Plant Available Water
Water may be present in the soil at the depth of the plant roots, but it must be available to the plant. Soil water, atmospheric conditions and plant parameters factor into transpiration. The energy exerted by the plant to draw water from the soil and the soil type are factors in moisture extraction.
Sterling, Tracy M. “Transpiration – Water Movement through Plants.” 2014. Plant and Soil Sciences eLibrary, University of Nebraska – Lincoln. Accessed December 10, 2014. http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1092853841&topicorder=1&maxto=8&minto=1.
“Field Capacity, Permanent Wilting Point & Available Water Capacity.” 2010. Northeast Region Certified Crop Advisor Study Resources, Cornell University. Accessed October 31, 2014. http://nrcca.cals.cornell.edu/soil/CA2/CA0212.1-3.php.
Supplemental Water through Irrigation
Responsible addition of supplemental water may be necessary to meet plant health goals. Plant water needs at various growth stages and depths, water holding capacity and precipitation are all factors that contribute to the decision to irrigate and the management-allowed deficit formula helps with quantities. For additional information on irrigation systems, see the unit covering residential water systems.
“The Effective Root Zone as a System.” 2005. Center for Irrigation Technology, California State University-Fresno. Accessed December 5, 2014. http://cwi.csufresno.edu/wateright/Sched1.asp.
“Estimating Soil Moisture by Feel and Appearance.” 1998. U.S. Department of Agriculture, Natural Resources Conservation Service, Program Aid Number 1619. Public domain. Accessed October 31, 2014. http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_051845.pdf.