Better Landscaping Today Newsletter

Volume 2, Issue 8                                                                                                                                 August 1999

CONSERVE WATER AND STILL USE CONVENTIONAL PLANTINGS

Because of apparent drought, some state agencies and municipalities are now discussing and enacting regulations for water conservation.  One area of high water consumption and of great concern is landscaping.  How much water do you believe could be saved by using available technologies and still use conventional plants? 10%? 20%?  Would you believe 50%?

On the average in Southern California, landscape plants need from 30 inches of water a year along the coast to 50 or 60 inches in the Inland Empire.  Rain supplies 15 inches of the need in Los Angeles for most years.  Supplemental irrigation will need to be 15 to 45 inches in most years.  Much more water is usually applied over and above that of plant needs and a major portion of excess applied water never enters the soil.  It is lost as run-off water.

The Fate of Soil Water

After the water does get into the soil, it can remain there or be removed by evapotranspiration.  Evapotranspiration means that the water is evaporated either from the soil surface or from the leaves of plants in the process called transpiration.  Besides transpiration, the causes of water loss from the soil are evaporation and water movement below the root zone.  Evaporation may be the cause of the greatest loss from the soil.  Four major statements concerning evaporative losses are:

1.  The evaporation rate is proportional or related to the water content of bare untilled soil.

2.  The evaporation is proportional to the rate at which water comes to the surface from fine capillary pores.

3.  The evaporation rate is proportional to the square root of the soil temperature.

4.  The evaporation rate is inversely proportional to the relative humidity and wind velocity.

WATER CAN RUN OFF, EVAPORATE, OR DRAIN AWAY

Allowing the soil to partially dry before a subsequent irrigation not only helps conserve moisture by decreasing evaporative loss, but it also improves the soil aeration and helps promote deeper root growth.  This helps improve plant appearance and utilizes deeper soil moisture and hence increases water utilization efficiency.

Soil contains pores.  Water moves through the small pores by capillary action because of the surface tension of water.  This is the physical property which causes water to bead up.  Evaporation of moisture on the soil surface dries the soil on the surface.  Moisture then moves upward by capillary action to equilibrate the soil moisture, and it in turn evaporates.  Capillary losses can be lessened by decreasing the capillary pore continuum with. the soil surface or through the use of mulches.  Studies by Carl Eser many years ago found that 1/4 inch of chopped straw reduced evaporation 50% and that 2 inches reduced it 90%.  A mulch also decreases soil temperature which can also be accomplished with well established ground covers or sufficient trees due to solar shading.

A mulch need not be a non-soil material.  Soil for example can be used as a mulch.  F. H. King measured water loss for 100 days in a clay loam soil which had been tilled and compared to non-tilled soil.

EFFECTIVENESS OF SOIL MULCH FOR CONTROLLING EVAPORATION

Depth of Mulch                        Water Loss, in inches  during 100 days

0 inch                                                      21.31

1 inch                                                      11.13

2  inches                                                    8.65

3  inches                                                    7.85

4  inches                                                    7.80

In a year's time, loose, friable surface soil could probably save over half of the water in the above case.  Unless the soil has been amended with stabilizing agents such as Soil Drain, tillage will be required after each irrigation to reform friable soil.  This is because unstabilized soil particles reconsolidate in the presence of water which forms compacted soil with capillary pores.

In addition, Soil Drain polymer increases the soil porosity.  Aeration is enhanced as is water infiltration which decreases water run-off.  Of course, excess irrigation needs to be avoided in order to eliminate excess deep water movement.  Reduced erosion is also accomplished along with water conservation.  Another water conservation benefit is larger crumb size found in polymer treated soil.

SOIL CRUMB SIZE PLAYS A MAJOR ROLE IN RATE OF EVAPORATION

Particle size and state of aggregation exerts a significant influence upon evaporation.  Carl Eser discovered that if his experimental soil screened to be less than 71 microns (3 thousands of an inch) were taken as 100%, the evaporative loss could be reduced 19% for soil when the particles varied from 1/50 to 1/00 inches.  Moisture loss for crumbs between 1/10 and 1/25 inches was reduced 78%.  Soil Drain can help form and maintain these larger particle sizes.

Water conservation can be successfully implemented with the soil polymer technology.  Polymer-treated soil gives not just a prettier landscape but one that is less expensive to maintain.  The length of irrigation cycles and their frequencies can be lowered.  This is possible due to less evaporative loss, less water run-off, deeper rooted plants and fuller plant canopies, all possible with well structured soils which result from use of polymers.  Your clients will like what Soil Drain can do for them, especially for its ability to help conserve water.

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