Laserfiche WebLink
r <br /> Total Available Moisture <br /> + Thi: total amount of water available for plant use in the root zone is the sum of the AWC per foot <br /> for !the various soil types within the effective rooting depth. See the example 1 (page 3, Appendix <br /> When To Irrigate <br /> i <br /> i Most surface-irrigated crops are normally irrigated when about 50 :percent of the available <br /> E moisture has been removed. Exceptions would be specialty crops needing certain conditions for <br /> pro�uct quality. <br /> > One method of estimating the amount of water depleted from the soil is the "feel" method, using <br /> Table 3 (Appendix C). The depletion level estimates can be made by taking soil samples at <br /> various locations in the field with an auger, soil tube, or shovel at approximately 1-foot increments <br /> for the entire crop root zone. The total amount of moisture depleted at each location is the:sum of <br /> 1 <br /> the:1-foot increments for the crop rooting depth. This is also the new amount to be replaced by <br /> irrigation in order to refill the soil profile to its capacity. Additional allowance must be made for <br /> deep percolation, runoff losses, salinity leaching, and application efficiency. <br /> If crop evapotranspiration (ETc) (see Appendix C for "crop coefficients" explanation) is used for <br /> the irrigation scheduling, the crop should be irrigated before the sum of daily ETc since the last <br /> } irrigation exceeds the "allowable depletion" (see site specific calculations below) from field <br /> capacity. This ensures that the soil-water content will not fall below the yield threshold and reduce <br /> yield. <br /> For the Site Soils, the Field Capacity is: <br /> Jacktone clay 23.00" <br /> Madera sandy loam 17.12" <br /> Manteca fine sandy loam 16.67" <br /> Stockton clay 25.08" <br /> To find the permanent wilting point, subtract the available water from field capacity. Thus, the <br /> permanent wilting point is: <br /> F, Permanent Wiltinq Point . . . <br /> Jacktone clay 14.58" <br /> F. Madera sandy loam '10.72" <br /> Manteca fine sandy loam 8.60" <br /> Stockton clay 16.04" <br /> The values calculated above indicate the unavailable water, which plants cannot extract. <br /> See Page 47 for References and Bibliography <br /> O Western Dairy Design Associates, Inc.2003 <br /> Page 36 <br />