Irrigation Scheduling on Barley
and Durum Wheat
A study was done on durum wheat and barley to determine the economical consequences of irrigation scheduling. Delays of 3 days and 7 days were applied after AZSCHED software called for irrigations to similate a wait for water from the irrigation canal. Yields were reduced by the delays, but with the crop values reduced by the cost of irrigation no money was lost in delaying irrigations on the durum wheat and $8-9 per acre was lost on the barley.
AZSCHED irrigation scheduling software was used in this study to aid the researchers in applying water at prescribed soil moisture depletion levels. The intention of this study was to use a given soil moisture depletion level to call for irrigations and then deviate from the dates that irrigations were called for by a given number of days to simulate waiting for a water turn. The results would then be used to help grain growers develop irrigation strategies.
Materials and Methods
In preparation for this study the ground was disced and furrows were pulled on 3-foot centers. Grain was then planted on a four-two skip pattern. In other words, four rows were planted and two rows were left unplanted. The unplanted rows were then shaped into a border which separated the irrigation treatments. The cultural practices that were used are listed in the crop history below:
Plots were combined with a Gleaner Combine with a 13 foot header. Grain was caught in buckets as it exited the clean grain auger, where it was weighed and samples collected for bushel weight and moisture determination. Grain weights were all corrected to 12% moisture to determine yields.
Results and Discussion
Table 1 shows the irrigation parameters in the studies of both durum wheat and barley. The irrigations and rainfall are actually measured or estimated data whereas the last three columns were calculated from AZSCHED irrigation scheduling software. For the durum wheat study, it is interesting to note that the 40% depletion treatment with the 3 day and 7 day delay had the same number of irrigations and approximately the same amount of water applied. This probably occurred due to human error in the administration of the experimental design. Figures 1 and 2 show the frequency of irrigations and the calculated percent depletion levels. The average depletion level is all of the daily values of soil moisture depletion averaged together from the time the crop was watered up to physiological maturity (6 June). The average depletion trigger was the average of the calculated percent soil moisture depletion levels when irrigations were applied.
The yield and other agronomic values for the durum wheat study are shown in Table 2. The plots with the least moisture stress (lowest average soil moisture depletion and the lowest trigger level) had the highest yields. The 40% depletion plots had the highest yield with the 50% depletion plots coming in second. The least stressed plots also tended to have taller plants, but no statistical differences were seen.
Table 3 lists the yield and other agronomic values for the barley study. The correlation between yield and average depletion level and depletion trigger is not as good as in the case of the durum wheat, but the slope of the line is the same. Plots with less stress tended to have better yields.
Table 4 gets to the meat of the study; where is the economic balance between trying to supply the crops water needs and the monetary rewards? Grain values are calculated using $8/cwt for durum wheat and $5/cwt for barley. Irrigation costs are calculated using information from the Arizona Field Crop Budgets - Graham County (1). The figure of $17 per irrigation is an estimation of the cost of an average irrigation in the county, using some river water, some well water and the labor costs to apply the water. It is interesting to note in both the durum wheat and the barley, the most cost efficient irrigation scheduling was to water at 50% soil water depletion level. The study on barley last year (2) favored the 40% depletion level, but that was because the value of the crop was higher then during the current year. Yields were very similar between the two years.
The cost of delaying the irrigation 3 days or 7 days from the 40% depletion level were negative in the case of durum wheat and only $8-9/acre for the barley. More data are needed to make recommendations.
1. Daugherty, Lew and Ron Cluff. 1996. 1996-97 Arizona Field Crop Budgets - Graham County. The University of Arizona, College of Agriculture, Cooperative Extension Bulletin #196013.
2. Clark, L.J. and E.W. Carpenter. 1997. Irrigation scheduling on barley at the Safford Ag Center, 1997. Forage and Grain, A College of Agriculture Report, The University of Arizona, Tucson, AZ. Series P-110, pp. 133-136
This is a part of publication
AZ1059: "1998 Forage and
Grain Agriculture Report," College of Agriculture,
The University of Arizona, Tucson, Arizona, 85721.