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Optimum design and management of irrigated wheat production is limited by the scarcity of information available on yield variability. The purpose of this study was to evaluate the spatial variability in soil-water parameters and the effects compared to grain yield response under level-basin irrigation. Three levels of seasonal irrigation water and two border lengths were used. Grain yields were found to increase significantly with the amount of water applied and soil water depletion (estimate of crop evapotranspiration), although yield variability was greater with reduced or deficit irrigations. Variations in soil water content were responsible for about 22% of the variability in grain yield, indicating that other soil and crop- related factors had a significant influence on production. Spatial dependence was exhibited over a greater distance at the wetter compared with the drier irrigation regimes.

One-irrigation barleys have been selected for performance with a pre-plant irrigation to fill the soil to field capacity to a depth of 5 feet. The barley is then grown with no additional irrigation, which simulates conditions of the North African coast. In this study, two of these barley selections were planted at four planting rates at three dates in Marana to determine optimum seeding rates. A seeding rate of 20 lbs /A resulted in greater yields than 40, 60, or 80 lbs /A when the data were combined for all planting dates.

Several improved irrigation scheduling methods are available to farmers to reduce the amount of water used while not reducing crop yield. Each scheduling method has its own advantages and disadvantages. Because of the disadvantages, farmers have been slow in adopting some of the newer irrigation scheduling methods. This study compares two improved scheduling methods, the neutron hydro probe and a simplified bookkeeping method using a personal computer, with the irrigation practices normally used by a farm manager to grow wheat. In addition to the traditional parameters of applied water and yield, the time and difficulty associated with each method were evaluated.

The relative ability of barley cultivars to perform outside the environment for which they were selected is not fully known. This study was initiated at Marana in 1985-86 to compare barley cultivars, which were adapted to different input levels, under a line-source sprinkler system that delivered a gradient of water. Higher than average rainfall in February and March provided ample moisture for crop growth, prevented very low water levels and led to the water gradient being applied late in the season when most of the cultivars were in the grain fill stage. We determined that cultivars bred for high level management (Gustoe and Barcott) performed best at the high water levels. Suitable cultivars for minimal water could not be determined since truly low water levels were never attained. Harvest index, the proportion of grain to total plant yield, was greatest for Gustoe at the high water level, but no differences were detected at the low water level. We suspect that one-irrigation barleys, bred to produce grain with a single preplant irrigation, effectively recover water with a deep root system and do not necessarily use less water than other barley cultivars.

An irrigation study on barley was made to determine the economical consequences of irrigating the crop when an irrigation scheduling program called for an irrigation compared to waiting 3 to 6 days for a water turn, from the ditch. The plots irrigated when the soil moisture depletion level reached 40% produced the highest yield. Yields were decreased 700 and 1000 pounds respectively for waiting 3-4 days and 6-7 days, respectively. The economics of using the pump are discussed and a chart is given to help determine a break - even point.

Solum is a barley adapted to one or two irrigations but the grain produced is often low in test weight. Studies were conducted on two commercial farms near Maricopa and Coolidge in an effort to verify data from previous studies suggesting that delaying the first post-emergence irrigation until boot increases test weight compared to earlier irrigation, but does not affect yield. The irrigation treatments consisted of 1) two irrigations – planting and boot, or 2) three irrigations – planting, 5- to 6-leaf stage, and heading (grower standard). The irrigation treatments had no effect on grain yield, test weight, kernel weight, or lodging at either location, but delaying the second irrigation until boot reduced plant height at Coolidge. Despite the lack of positive results from these studies, applying the second irrigation at boot may still be preferable to earlier applications because of reduced plant height and the risk of lodging. We have not been able to measure a benefit from a third irrigation for Solum barley in these or previous studies.

This research represents the second year of a project to determine when to irrigate barley based on soil water depletion levels. The purpose of this work is to establish the optimum irrigation timing based on depletion of plant available water in the soil. A field experiment was conducted at the Maricopa Agricultural Center testing irrigation of barley at 35, 50, 65, and 80% depletion of plant available water in the soil for two barley varieties, Baretta and Max. Grain yields for the 35, 50, 65, and 80% depletion levels were 8319, 7296, 5606, and 3404 lbs/acre for Baretta and 9164, 8403, 6463, and 3416 lbs/acre for Max, respectively. The yield increase averaged across varieties from irrigating at 35% rather than 50% depletion is 893 lbs/acre, which has a value of $45.54/acre assuming a grain price of $5.10/cwt. However, the cost of producing this grain is $54.33/acre due the cost of two additional irrigations ($44/acre), 30 lbs additional nitrogen per acre ($8.10/acre), and increased hauling cost ($2.23/acre). The profitability of irrigating at 35% rather than 50% depletion is improved with an increase in grain price or decrease in water cost.

This research was conducted to test the effect of soil water depletion levels on durum productivity. An experiment was conducted at a commercial farm in Stanfield where irrigations were applied at 35, 50, or 65% depletion of plant available soil water. These soil water depletion levels were estimated from soil texture and weather data. The grain yields obtained with 35, 50, and 65% depletion were 6718, 6324, and 4752 lbs/acre, respectively. Grain protein decreased and HVAC increased by irrigating more frequently at lower depletion levels. Irrigating at 50% depletion was the most economical in this study considering irrigation costs and grain quality discounts.

The AZSCHED irrigation scheduling software was developed in the early 1990's to be used in a DOS environment on computers (1) and has been used extensively for irrigation scheduling on the Safford Agricultural Center since its development. The new Windows version of AZSCHED (2) was first tested for barley and wheat in 2003. This is a follow-up verification to the first test using a wider range of irrigation depletion levels.