In a recent meeting the topic of where to go for irrigation information came up. Well there's no substitute for attending a class in irrigation, such as offered at Cal Poly SLO (http://www.itrc.org/classes/iseclass.htm ,
but here's some written sources to get you started thinking.
http://ciwr.ucanr.edu/california_drought_expertise/droughttips/
http://www.salinitymanagement.org/Salinity%20Management%20Guide/ei/ei_1.html
http://www.avocadosource.com/tools/IrrigationCalculator.asp
http://lawr.ucdavis.edu/cooperative-extension/irrigation/manuals
http://lawr.ucdavis.edu/cooperative-extension/irrigation/drought-tips
http://biomet.ucdavis.edu/index.php/evapotranspiration-mainmenu-32