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Two-year studies (1979-1980, 1980-1981) designed to measure the relation of plant development to yield of spring wheats were undertaken at the University of Arizona Mesa Experiment Station and at the Casa Grande Overpass Farm, Tucson. Low density seeding rates (15 to 20 kg/ha) were used in both studies. The soil at Mesa and in Tucson were clay and sandy barns, respectively. All plants grown under limiting water conditions received 150 kg/m² pre-plant irrigation. Supplemental water as rainfall in the 1979-1980, 1980-1981 seasons were 153 and 79 kg/m² atMesa respectively, and 134 and 116 kg/m2 in Tucson for the respective seasons. Experiments were also conducted in Tucson during the two seasons to evaluate yield performance of wheats under well-watered conditions (525 kg 1m2 and 400 kg/m² irrigation water in the 1979-1980, 1980-1981 seasons, respectively) and on plants which received a single added irrigation approximately 2 to 3 weeks prior to the estimated time of anthesis. Yields in Mesa ranged from 2400 to 3700 kg/ha in 1980 and from 1800 to 3600 kg/ha in 1981. When grown under limiting water conditions in Tucson yields ranged from 1100 to 3000 kg/ha in 1980 and from 2000 to 4100 kg/ha in 1981. Productivities of plants grown with a single added irrigation ranged from 2000 to 4200 kg/ha. Under minimal water conditions yield was correlated with head weight of the main culm, average head weight, grain weight per spike, number of grains per unit land area, Leaf area and Flag leaf area indices at later stages of development, total plant dry weights, root depths and dry weights. Differences were found in tissue water status and leaf growth of selected entries. Tissue water potential was higher in a higher yielding than in a low yielding entry. Additionally, tissues at the basal region tended to be more "sensitive" to changes in soil moisture than those at the mid-section of the expanding leaf. Difficulty in sample selection and variability with plants militated against using leaf growth as an index for determining the degree of stress in field grown wheat cultivars. Neutron probe analysis of soil profile water depletion of a high yielding, long rooted cultivar was greater at the lower depths (60 to 120 cm) after anthesis than for an intermediate or low yielder.

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.