Another winter with low rainfall will challenge central Arizona growers in the months ahead as irrigation water becomes an even more precious commodity. Producing a quality product that meets market demands and enhances Arizona's position as a producer of quality alfalfa and other forages will challenge management skills.
Gathering as much information on water management and “deficit irrigation” is obviously the most important task that needs to be addressed.
However, there are other related management issues that require attention. Optimum weed control, for example, enhances forage quality and eliminates plant competition for water. In addition, a well fertilized crop is better able to cope with water stress when irrigation programs are cut back. Other stress factors such as insects also need to be dealt with, as well.
A wide range of information is available from the University of Arizona and other sources on irrigation management and monitoring tools that can help pinpoint optimum timing and get maximum results with the amount of water that's applied. Also, don't overlook soil amendments that increase infiltration and more uniform distribution of water in the soil profile.
According to the U of A (www.ag.arizona.edu/forageandgrain/), seasonal water use for alfalfa in the Phoenix area is about 74 inches. The question of whether terminating summer irrigation will hurt alfalfa stands depends on factors such as summer rainfall, availability of deep soil moisture, soil type and temperatures. An indicator of moisture stress is the moisture status of the crown and root. If greater than 60 percent, alfalfa is well watered, 50 percent to 60 percent indicates a water-stressed crop, 40 percent to 50 percent signals severe water stress and less than 40 percent is “lethal water stress.” Among the tools available on the Web is the “Arizona Irrigation Scheduling System” (AZSCHED), which can be downloaded from http://ag.arizona.edu/crops/irrigation/azsched/azsched.html.
The U of A's Web site also has links to other sites that have irrigation management information, including the “Forage Information System,” http://forages.oregonstate.edu. It compiles a wide range of data from national and international sources.
One of the keys to top-notch irrigation management is the use of water monitoring tools, a subject that was covered in depth at the California Alfalfa and Forage Symposium last December. The range of tools available runs the gamut from simple steel rod probes to tensiometers, resistance or gypsum blocks, to highly sophisticated technologies such as neutron probes and capacitance probes. More water management information and past Symposium proceedings are available at http://alfalfa.ucdavis.edu.
Sorting through the information that can be gleaned from the Web and other sources may seem like an overwhelming task. On the other hand, water availability will become a greater challenge for Arizona producers.
Alfalfa acreage in Arizona has increased steadily since 1993, when alfalfa hay was harvested from 150,000 acres, and reached 225,000 acres in 2002. Corn silage acreage has increased from 5,000 acres in 1992 to 33,000 acres in 2002. Future growth and economic success for Arizona's alfalfa and forage producers will depend on managing for maximum quality and utilizing available water as efficiently as possible.