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Practid Approac~or EBcctive E ~ S Conwl - 90 <br />whether or not it gives up this moisture for plants. In acid climates the <br />percentage of water available for plant use may be in fact the most critical <br />variable in the long term erosion control effectiveness of a system. A surface <br />applied or incorporated mulch may reduce runoff by absorption or adsorption, <br />but the retained moisture serves has no benefit to plants unless that water is in <br />proximity to plant roots or held at tensions where it can be available to plants. <br />Field Notes: For quantitative measurement of percentage moisture retention by <br />weight, standard ASTM test methods for geoteuiles can be employed. <br />AS Available Moisture in Soil <br />Some BMPs are better than others at preventing soil from drying out, and <br />keeping moisture available for plants. For a quick, quantification of available <br />soil moisture, a soil tensiometer or a soil bridge can be employed. These <br />apparatus measure the resistance an electrical current encounters when it passes <br />through soils of varying moisture content. <br />TM Temperature Modification <br />Similar in some respects to increasing available moisture, some BMPs moderate <br />the temperature of the environment for plants and thereby influence germination <br />and growth. In some respects, where a surface cover is concerned, color may <br />play a major role in reflecting or absorbing sunlight. Whether or not <br />temperature modification is important depends a great deal on the geographic <br />azea of application and slope aspect (the direction in which a slope is facing). <br />For example, a surface applied organic mulch which reflects heat might be <br />advantageous on a south facing slope where it reflects sunlight, modifying <br />temperature and retaining moisture in the soil for developing plants. On the <br />otherhand, the same mulch applied on a north facing slope late in the fall might <br />stow soil warmup in the spring, retain too much over-winter moisture and cause <br />seed rot. <br />Field Notes: Temperature modification can easily be determined by measuring <br />the soil temperature of an untreated area and comparing it to soil temperature <br />from a neared area. Ambient air temperature above the treated sail surface can <br />also be compared to soil temperarures in the soil below. <br />O 1995 IECA <br />