Field-scale Demonstrations of the
Timing of the Last Irrigation in Wheat

S. H. Husman and M. J. Ottman


The last irrigation of wheat can be applied at the soft dough stage or for a sandy loam soil according to crop water use calculations. The purpose of this study is to verify at what stage the last irrigation of wheat should be applied. Studies were conducted on 7 commercial fields where the last irrigation was applied at the soft dough stage or about 10 to 14 days after soft dough. Applying the final irrigation after the soft dough stage does not appear to increase yield on average according to the results of this study. 


When to apply the last irrigation to wheat is commonly a difficult decision for growers. Applying an irrigation that is not necessary wastes resources and could induce lodging. Conversely, not applying a final irrigation can result in shrunken kernels and reduced yield. Previous work (Ottman and Husman, 1997) and calculation of crop water requirements at the end of the season suggest that the last irrigation of wheat should be applied at the soft dough stage. The objective of this work is to verify in a commercial setting when the last irrigation should be applied to wheat based on crop growth stage and soil type.


This work was conducted on 7 commercial durum fields in Pinal County. The variety planted was Ocotillo at the Pacheco and Schlittenhart locations. The fields were treated normally until the last irrigation. In some cases one more irrigation was applied than the standard farm practice, and in other cases, one less irrigation was applied than standard farm practice. In either case, an irrigation was applied near soft dough, and additional irrigation was applied 10 to 14 days thereafter. The size of the plots was about 3-4 acres each or the size of an irrigation set. The soil was sampled at these sites to a depth of 4 feet to characterize them in terms of soil texture and water holding capacity. Grain heads were sampled and analyzed for moisture content to obtain a more accurate estimation of growth stage. The grain was harvested in a strip in the plot area with a commercial combine and weighed for yield determination. Grain samples were analyzed for test weight, kernel weight, HVAC, and protein content. 


The influence of the final irrigation on grain yield and kernel characteristics is presented in Table 1. Applying an additional irrigation after the soft dough stage did not affect yield on average. At the Schlittenhart farm, however, applying an irrigation after soft dough appeared to increase or decrease yield depending on the field. Test weight and HVAC were not affected by the timing of the last irrigation. Kernel weight was increased slightly by applying an irrigation after soft dough. Protein was also increased by the additional irrigation. These results suggest that applying an irrigation after soft dough is usually not beneficial.


  1. Ottman, M. J., and S. H. Husman. 1997. The last irrigation in durum at Buckeye, Casa Grande, and Marana, 1996-97. pp. 137-140. Univ. Ariz. Coop. Ext. Ag. Exp. Stn. Report Series P-110, Tucson.


The cooperation of the following growers is appreciated: Marvin Wuertz, Paul Ollerton, Bill Scott, Dan and Todd Thelander, Brian Hartman, Russ Schlittenhart, and Pat and Lyall Pacheco. The technical assistance of Mark Rogers and Randy Wegener was critical to completion of these trials. Financial support for this project was received from the Arizona Grain Research and Promotion Council.

This is a part of publication AZ1059: "1998 Forage and Grain Agriculture Report," College of Agriculture, The University of Arizona, Tucson, Arizona, 85721. 
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