Judson Sullivan and Alison Scheetz - Spring 2005

  
   
Introduction  
   

There is a clear understanding of the importance of protecting both the quality and quantity of our water resources. Many landscapes currently require a significant volume of irrigation and a strict regime of chemical fertilization to maintain plain health and aesthetics. This is often due to developers focusing on the short term costs of development with little consideration of the importance of good soil preparation and its long term benefits. This practice of inadequate soil preparation results in long term maintenance, irrigation, and plant health issues.

The subsequent irrigation and fertilization regimes that are required to sustain plant health in these tragic systems have a detrimental effect on both the quality and quantity of the water supply. It is difficult to properly amend and prepare soil once a landscape has been installed. But, if soil is appropriately amended and vigorous plant growth is encouraged, the capacity of a site to filter urban pollutants is greatly increased. Although practices of mulching, composting, and amending the top few inches of the soil are all helpful in boosting plant and soil health, there is truly nothing as effective as proper soil preparation prior to planting.

n this investigation we will look at some ways in which amendment of the soil, and subsequent mulching and composting can effectively maintain a healthy landscape. This also minimizes the demand for irrigation and enhances water quality by severely reducing the need for chemical inputs (fertilizers, herbicides, and pesticides) through maintaining a healthy soil ecosystem.

 

Soil texture and water quality

Understanding soil texture is crucial to deciding on an effective soil management strategy to improve and maintain soil health and water quality.

A soil's texture is defined by the size of its primary particles. There are three types of mineral particles: clay, sand or silt. Clay has the smallest particles, sand the largest, and silt particles are intermediate in size.

While most soils have a mixture of all three types of particles, soil texture influences water flow and penetration, as well as the ability for contaminants to leach into ground water. Good soil and water conservation practices are recommended for all soils; however, there are a number of risks associated with particular soil textures that should be considered.

  
Clay soils

  • Soils with high clay contents have several properties which may lead to movement of contaminants.

  • Surface structure can become degraded in clay soils, forming a crust. Crusting limits infiltration and increases runoff.

  • When wet, clay soils are easily compacted, which also increases runoff. The runoff may contain contaminants and could affect the quality of surface and ground water.

  • Clay-sized sediment, because of its very small size, is very slow to settle out of dugouts, streams and lakes, which can greatly affect the quality of water.

  • Clay soils may also be highly susceptible to wind erosion. During dry conditions, the surface of heavy clays may become pulverized to a condition where clods are the size of large sand grains. Particles of this size are highly susceptible to wind erosion.

 

Sandy Soils

  • Sandy soils have relatively large spaces between particles, which provide for rapid downward water movement. Substances, dissolved in leaching waters, are readily transported deep into the soil, and potentially to groundwater.

  • Sandy soils are also have poor structure and, as a result, are highly susceptible to wind erosion. They are coarse-textured and dry out quickly, which tends to increase wind erodibility.

  

Silty soils

  • Although all soils are potentially susceptible to water erosion, silts, silt loams and loams are most at risk. Water erosion is greatly increased on long or steep slopes where runoff can reach high velocities. Surface runoff of both dissolved and attached compounds occurs during a water erosion event.

  • Although it can be quite difficult to alter soil texture on a large scale, many of the problems associated with soil texture can be mitigated through the application of soil amendments, compost and mulching. Amending or mulching soils with a high quality compost alone can have multiple benefits such as: Erosion control, increased water retention, surface porosity and soil fertility.