Wheat irrigations were scheduled using two computer models and an infrared thermometer, using three critical threshold values. Yields from these plots were compared with plots scheduled by the farm manager. The highest yield was obtained by the computer model using evapotranspiration data taken from the local AZMET station; this corroborates results from the previous year. The crop coefficients and the irrigation model that have been developed over the past several years are very accurate for this area. The two lower threshold infrared treatments were second and third in yield and had lower water use efficiencies.

Twelve oat varieties (9 hulled and 3 hull-less) were yield tested for both forage and grain production at the Maricopa Agricultural Center during the '89-90 growing season. Highest forage producing varieties were generally later maturing - Cayuse and Stampede; while lower yields were produced by early maturing varieties - Montezuma and Palestine. Highest grain yields were produced by Swan and FMC400.

No description available.

A field experiment was conducted on a Casa Grande sandy loam at the Maricopa Agricultural Center to 1) determine the optimum rates of late season N needed to achieve optimum yield and quality of irrigated dumm wheat in conjunction with varying rates of early season N, and 2) to evaluate the usefulness of stem NO₃⁻N analysis in predicting the late season N rates which optimize grain production but minimize the potential for nitrate pollution of groundwater. The application of 80, 195 and 350 lbs. N/a during vegetative growth resulted in wheat with deficient, sufficient and excessive N status at the boot stage as indicated by stem NO₃⁻N analysis. The application of 60 lbs. N/a at heading to N-deficient wheat and 15 lbs. N/a to N-sufficient wheat resulted in grain protein levels above 14% but had little effect on grain yield. Applications of N at heading to wheat which had previously received excessive N did not affect grain yield or quality. The use of stem NO₃⁻N analysis appears to be a useful tool in predicting the minimum N rate to be applied during the early reproductive period to insure acceptable levels of grain protein at harvest.

Yield trials were conducted at the Maricopa Agricultural Center during the '89 -90 growing season. Barley, durum and wheat varieties as well as experimental lines from various seed companies were tested for yield performance. Gustoe and two experimental lines, 7024 and PHS84-11, were the highest yielding barley entries. Aldura, Turbo and Aldente were the top yielding durum varieties. 911, Probred and BR5738-1 were the top yielding wheat cultivars.

Seeding rates of wheat and barley varying from 50 to 250 pounds per acre were planted at four or five planting dates from the 1987-88 season to the 1989-90 season. Optimum seeding rates for wheat seemed to be near the upper limit whereas for barley it fell between 150 and 250 pounds per acre. This is considerably higher than what is commonly recommended in other parts of the state.

Canarygrass (Phalaris minor) has become an increasingly widespread weed in wheat grown in central and southwestern Arizona. Only two herbicides, Barban and Diclofop, have been used effectively to control this weed. The registration of Barban was dropped in 1989 and the labeled rate of Diclofop was lowered to marginal control levels in 1990. A test was conducted to evaluate potential new treatments for the control of canarygrass. One treatment; Puma at 1.14 lbs./A resulted in excellent control of this weed.

Forage trials of four crops grown under high-input and low-input production cultures were performed at the Maricopa Agricultural Center. Six varieties of each crop were grown to evaluate yield potential under both production cultures. Only a preplant irrigation was applied to the low-input culture, but up to four additional irrigations were applied to the high-input culture. No fertilizer application was given to low-input, but a total of 135#N/A and 75#P₂O₅/A was applied to the full production culture. Barley, durum, and wheat cultivars developed for grain yield under a low-input production culture were tested for forage production under both high- and low-input practices. No advantage in forage production was observed by using the following varieties in a low-input production culture: Stampede oats, Westford barley, Mexicali durum, and 911 wheat produced the highest yields in each of the four crops. Yields were greater from crops grown under a high-input culture: Stampede oats, Harlan II barley, Aldura durum, and 911 wheat were highest yielding varieties in each crop.

Four irrigation scheduling methods are compared over a three year period on the Safford Agricultural Center. A computerized checkbook method based on the consumptive water use curves of Erie, et al, updated with near real time evapotranspiration data from the AZMET system and utilizing empirical crop coefficients, produced the highest yields and with the highest water use efficiency. Scheduling irrigations with the IR thermometer produced yields higher than the Check when a Stress Index threshold of 2 (similar to a CWSI of 0.2) was used, but not with a threshold value of 3 nor 4. A method of irrigation scheduling using Erie's curves, but not updated for current weather values, yielded less than the check in all years of the study, and was not considered an acceptable method Irrigation inputs from the 1990 season were plugged into new near real time irrigation scheduling software which utilizes AZMET data to determine both evapotranspiration and crop coefficients. This method was found to track the field data quite well and will be utilized in future research.

Durum wheat (Triticum turgidum L. var. durum ) is grown as a winter annual crop, normally in rotation with cotton, and in 1989, comprised 121,500 acres in Arizona. Winter rainfall is insignificant, therefore water is supplied totally through surface irrigation. The relationship between the timing and amount of irrigation water applied and grain yields have not been well -defined Field plot studies were conducted in 1986 and 1987 to test the feasibility of using the Crop Water Stress Index (CWSI) to time wheat irrigations and also to determine the relationship among the CWSI, grain production, and water applied The study was repeated at the commercial production level with a grower cooperator in 1989 to determine the usefulness of CWSI scheduling on large farms. Highest grain production was attained when irrigations were scheduled when the CWSI averaged 0.37 and 0.30 units on small plots for 1986 and 1987, respectively. At the grower production level, highest yields were attained when irrigations were scheduled when the CWSI averaged 0.17 units. In 1986 and 1987 scheduling irrigations at lower CWSI values did not significantly increase grain production while requiring more applied water than the optimum CWSI values. Scheduling irrigations at CWSI's exceeding the optimum values did significantly reduce grain production from the optimum, but required less applied water in all three years.