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<br />5 <br /> <br /> <br />water application since turf grass can not differentiate between irrigation water and precipitation. The <br />Gronning format ignores the precipitation component thereby modifying the deep percolation <br />response. Along with the inconsistent format between the two studies, the Cottonwood Curve and the <br />Gronning Line, have inconsistent results. Figure 2 shows the Cottonwood Curve and the Gronning <br />Line in both formats. Note that due to the quadratic relationship of water application and deep <br />percolation in the Cottonwood Curve, one function is linear and the other parabolic in each figure. <br /> <br />The different results between the two studies are due to several factors, the most significant <br />being that the Gronning Line is based on precipitation being removed from the total water application. <br />Another difference is that the two studies used soils specific to their sites, either dug from the <br />Iysimeter hole (Cottonwood) or using an undisturbed core (Gronning). <br />Both investigated the deep percolation response for their specific area. Other two factors affecting <br />each study's outcome are the water application amount and frequency. Neither the Cottonwood nor <br />the Colorado Springs studies were based on a regular irrigation amount and frequency. Both of these <br />factors were controlled by the individual homeowners who watered their lawns when they felt it was <br />necessary. This decision was based on homeowners' qualitative choice of how green they wanted <br />their lawns to appear, balanced with the expense and labor associated with the lawn irrigations. Both <br />studies are as much a "measure of human behavior" (Kaufman, 1996) of people in their areas as they <br />are about turf grass deep percolation. <br />