Field-scale Demonstration of Prevention of HVAC Dockage in Kronos Durum by Late Season Nitrogen Application  

S. H. Husman and M. J. Ottman



Grain quality is important to growers and buyers of durum. Growers are usually docked if their HVAC drops below 90% or their grain protein is below 13%. The purpose of this study was to demonstrate the ability of nitrogen fertilizer application near flowering to increase HVAC and grain protein. Six commercial sites were chosen for this study and Kronos was the variety. The application of about 50 pounds of nitrogen per acre increased HVAC by from 81 to 93% and increased grain protein from 11.2 to 12.3% on average, similar to results obtained in the past.



Research at the Maricopa Agricultural Center (Ottman et al., 1996) and on three commercial farms (Ottman et al., 1997) suggested that durum protein content may be increased by about 1% by applying 30 to 50 pounds of nitrogen fertilizer per acre from flowering to about 2 weeks thereafter. Flowering occurs about 10 days after heading in durum, and usually the last nitrogen fertilizer application is at flowering or before. Nitrogen fertilizer application after flowering is usually too late to affect yield unless nitrogen is deficient, but may be a method to ensure adequate protein content especially if yields may be higher than expected or previous nitrogen applications were not effectively utilized by the plant. 

Kronos is a commonly grown durum variety that farmers sometimes have difficulty making the 90% minimum HVAC. Low HVAC hurts the farmer, the grain company, and the reputation of Desert Durum. The purpose of this work is to demonstrate the effect of late season nitrogen application on HVAC and protein content of Kronos durum in a production setting. 


Six commercial fields of Kronos durum (except Bravadur at Thelander) were selected in Pinal County for these on-farm demonstrations. The fields were grown normally until the time of the last fertilizer application near flowering. Nitrogen fertilizer was applied near flowering at a rate of 35 to 50 pounds of nitrogen per acre to an area the size of an irrigation set (about 3-4 acres) and an adjacent area similar in size was left untreated. At heading and before the nitrogen was applied at flowering, the head and flag leaf were sampled and analyzed for total nitrogen and the lower stem tissue was sampled and analyzed for nitrate. After the grain was harvested, grain samples were obtained and analyzed for HVAC, protein, test weight, and 1000 kernel weight. 


The influence of late season nitrogen application on durum quality is presented in Table 1. Late season nitrogen application had no effect on grain test weight but increased 1000 kernel weight slightly. The application of about 50 pounds of nitrogen per acre increased HVAC by from 81 to 93% and increased grain protein from 11.22 to 12.32% on average. This is similar to the increases in HVAC and grain protein obtained in previous studies (Ottman et al., 1996; Ottman et al., 1997). HVAC was increased in 6 out of 6 cases and protein was increased in 5 out of 6 cases. The HVAC obtained with late N application was greater than the 90% desired by the grain companies. However, the protein content of 12.3% was less than 13% threshold desired for protein. 

A critical flag leaf N content of about 4% has been used as a guideline for late season nitrogen application in other regions to obtain adequate protein content in wheat. This guideline would not have provided adequate protein in this study. Stem nitrate content has been used locally for ensuring optimum yield, but its usefulness for determining adequate protein has been questioned. However, a critical level of 2000 ppm in the stem, for example, would result in nitrogen being recommended for the 5 out of 6 fields that had protein below 13%, and no nitrogen recommended for the one field that had protein above 13% without late season nitrogen application. The nitrogen content of the head does not vary much and may not be a useful indicator of nitrogen requirement to obtain desirable quality.


  1. Ottman, M. J., T. A. Doerge, and E. C. Martin. 1996. Late season water and nitrogen effects on durum quality, 1995 (Final). Forage and Grain. pp. 95-108. Univ. Ariz. Coop. Ext. Ag. Exp. Stn. Report Series P-106, Tucson. 
  2. Ottman, M. J., T. C. Knowles, and S. H. Husman. 1997. Late season nitrogen fertilizer for durum at Buckeye, Casa Grande, and Vicksburg. 1996-97. pp. 115-118. 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, and Brian Hartman. 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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