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An Excel spreadsheet from UC Cooperative Extension (copy attached) has been developed and calculates how much lagoon water each crop requires at each irrigation, based on the water t .= nitrogen content, and the stage of crop maturity. For total solids content of 0.5 percent or less, application rates in table 11--2 (Appendix C) (based on soil texture) can be used for irrigation system design and management to help avoid ponding and runoff. For total solids content in the liquid manure of 0.5per-cent or greater, application rates from the table.11-2 should be reduced according to the information in table 11-3 (Appendix C).The reduction coefficients in table 11--3 are based solely on decreases in hydraulic conductivity ' because of a layer of manure that forms on the soil surface during irrigation and has a lower hydraulic conductivity than the soil. Further reductions may be necessary in some situations, such as applications of liquid manure with salt concentrations sufficient to disperse clay aggregates. Salt content of the liquid manure will be determined to assess its effect of the intake rates of the soil where it will be applied. Irrigation Water Management .' An irrigation is scheduled when the amount of soil moisture depleted from the root zone approaches the allowable depletion level. The amount of water applied is based on replacing the depleted soil moisture. This involves decisions for when to irrigate and how much to apply in order to optimize moisture conditions for crop production and minimize irrigation costs. ` Occasionally, water deliveries are on a fixed schedule when deliveries are made every 10 to 15 days, Under these conditions, it is not necessary to decide when to irrigate, but only how much to apply. The amount applied then should be based only on the soil moisture depleted since the last irrigation. The relationship between the total amount delivered, delivery flow rate, set time, gross application, and the area to be irrigated is as follows: Total amount delivered = D x A = Q x T Where: D = Cross application depth (inches) A = Area irrigated (acres) Q = Flow rate (cubic feet per second) T = Set time (hours) This equation can be used to calculate gross application depth applied, the area to be irrigated, the flow rate required, and the set or delivery time. When the flow rate, time of set, and area irrigated are known, the gross application depth (D) can be calculated by: See Page 47 for References and Bibliography ©Western Dairy Design Associates,Inc.2003 Page 38