Is there any practical model available to estimate fertilizer and water requirements of crops in arid regions under irrigated farming?
In Saudi Arabia, both the soil and water are highly saline and all the crops are irrigated via a central pivot system, mainly wheat, barley, alfalfa and forage grasses. Vegetable crops are either grown in greenhouses or in the field using drip (subsurface or above ground) or sprinkler systems. Needed is a basic model to determine fertilizer requirements of crops for a target yield using data on oil fertility, temperature, relative humidity, SAR, water quality etc.
Information on irrigation water requirements for various crop species (including grains, grasses, alfalfa, and wheat) is included in a USDA Soil Conservation Service, Part 623 National Engineering Handbook, Chapter 2, Irrigation Water Requirements, printed September 1993. This publication also includes some basic information on salt tolerance and how to compute water needs.
We have no specific information on where you can get crop fertilization recommendations, but Extension Service should be a good place to start.
Dr. Donald Suarez has been leading a project to develop a generalized crop model for FAO that deals with salinity and crop yield. He is not aware of models for barley, forages, and alfalfa that take in to account and integrate all of the factors in which the question addresses.
Dr. Derrel Martin and others at the University of Nebraska have been working on water and fertilizer requirements under center pivot irrigation. You may want to direct your questions to Derrel.