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Colorado State University Master Gardener - Soil Water Holding Capacity and Irrigation Management Page 5 of 7 <br /> <br /> <br /> <br />These textbook figures make a good starting point to understand Irrigation management. Most automatic sprinkler <br />systems are set to keep the lawn green in the summer. (i.e., set for the higher summer water need). Without <br />I seasonal adjustments on the irrigation controller the lawn will be over-irrigated In the spring and fail by about <br />40%. This springtime over-irrigation Is a primary contributing factor to iron chlorosis. <br />t <br />Ether factors influencing irri&ation mama. a-ruent <br />Other factors also have a direct influence on the agtu.Ql water holding capacity and irrigation demands, for <br />example: <br />Soil organic matter content - Since organic matter holds over ten times more water than sand, a sandy <br />soil with good organic content (around 4-5%) will hold more water than Indicated in the table above. Over <br />time, clayey soils with good organic content may have an improved soil structure, supporting a deeper <br />rooting depth. <br />Previous irrigation pattern - Plants adjust rooting depth (to the extent that soil oxygen levels allow) to <br />where soil water is available. Frequent irrigation eliminates the need for plants to develop a deep rooting <br />( system. A shallow rooting system snakes the plant less resilient to hot, dry weather. <br />t . Stage of growth - The stage of growth also influences ET. Water needs Increase as a plant grows In size <br />f during the season, and peaks during flowering and fruit development. <br />l Compared to the rooting system of a mature plant, newly planted or seeded crops don't have the root <br />system to explore a large volume of soil for water. Recently planted and seeded crops will require frequent, <br />light Irrigations. In our dry climate, even "xeric" plants need regular irrigation to establish. <br />I <br />Water demand of a plant - Plants vary greatly In the demand for water to 1) support growth, and 2) <br />t <br />survive dry spells (note the two are net necessarily related). <br />i <br />Fine-tuninje for the site __ ?? <br />4 <br />The textbook figures are a good starting point to understand irrigation management. When coupled <br />with careful observations a gardener can quickly fine-tune his/her irrigation schedule to the site- <br />i speclfic irrigation demands. <br />. i <br />To the observant gardener, the lawn tells you when it needs watering. The color has a subtle change from bluish- <br />green to grayish-blue and footprints are still visible an hour or more later. The observant gardener can use these <br />4 <br />indicators to understand the water management for the site. <br />Look at the historical ET for the summer. On a typical June and July day, If the lawn is using 0.20 inches ET per <br />1 day, you can estimate the water holding capacity and rooting depth by observing Irrigation needs. <br />i <br />For example: <br />r ] a lavyp will gq 5 day,r1,.1 _inch of fir, and additional water won't extend the interval between <br />required Irrigation, the water holding capacity (for this soil and rooting depth) Is 1 Inch. one inch ryouid be <br />e maximum.:21.auo_f v?,ic_,tQ app?Y ner irria_ ta??on, sad itiona) apunts wgQ teach pe ow the ro.g <br />one., <br />Irrigation options include the following: <br />i <br />1 o Water every 5 days applying S inch of water, OR <br />a Water every n days applying 0.8 inches of water, OR <br />http:/twww.ext.colostate.edu/mg/files/gardennotes/261-Soi lWater.html <br />68 <br />1/3/2008 <br />