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<br />'0 u rJ 3 9 <br />Task 1.14(b) - Consumptive Use Prototype Development <br /> <br />Climate Characteristics i:..... <br />The amount of precipitation is important for determining the amount of irriga~ <br />water plants will consume. Knowing just the amount of precipitation is not enough, <br />the effective precipitation is the actual amount of precipitation used by plants and it <br />may depend on a host of factors not related to precipitation. In practice, effective ...-? <br />precipitation is the amount of water not needed from irrigation sources. <br /> <br />Temperature partly determines the evaporation and transpiration rates of agricultural <br />lands as well as the length of the growing season. Abnormally low temperatures may <br />retard plant growth and unusually high temperatures can produce dormancy. The <br />growing season is usually considered to be the period between killing frosts, though <br />for some plants the beginning of the growing season may come after the frosts and/or <br />the end of the season may be well before the fall frosts. <br /> <br />Latitude differences change the daily amount and seasonal duration of sunlight <br />available for crop growth. Higher northern latitudes experience much longer days in <br />the summer then in the winter. <br /> <br />Other climatic parameters that have an effect on the amount of irrigation water <br />consumed by plants includes relative humidity and wind movement. Hot dry winds <br />can significantly increase the rates of evaporation and transpiration especially in arid <br />and semi-arid climates. <br /> <br />Water Supply <br />Naturally, unless water is available from precipitation, groundwater, or irrigation <br />there can not be consumptive use from crops. In areas of the arid and semi-arid West <br />such as the Western Slope of Colorado the major source of water is irrigation. In these <br />areas the quantity and seasonal distribution of the available water supply will effect the <br />consumptive use characteristics of agricultural lands. Some studies have shown that <br />beside the quantity and seasonal distribution of the water supply, the quality of the <br />water also has an effect of consumptive use. Where soil salinity has begun decreasing <br />yields water supply might be increased to lower the salt concentration to the root zone. <br /> <br />Plant Growth Characteristics <br />The stage of a crop's growth has a very considerable influence on its rate of <br />consumptive use. This is particularly true for annual crops which generally have three <br />distinct stages of growth. These stages are the emergence and development of <br />complete vegetative cover characterized by the consumptive use rapidly increasing <br />from a low value to approaching its maximum value, the period of maximum <br />vegetative cover during which time the consumptive use will be near its maximum as <br />long as the water supply is available, and finally the maturation stage where, for most <br />crops, the consumptive use begins to decrease. <br /> <br />Effective Rainfall l"'l'~ <br />By definition, effective rainfall must,.a portion of a crop's water requirement, since it )0 <br />does not include water lost to surface runoff and/or deep percolation. Effective rainfall <br />is typically estimated from total rainfall for which data is available. The percentage of <br />total rainfall that is effective rainfall depends on soil conditions and climatic factors. In <br />arid areas where the total growing season precipitation is light and the soil profile is <br /> <br />7/13/94 - Draft of Task Memorandum <br /> <br />3 <br /> <br />IDS Group, CSU <br />