Use of grain protein concentration as an indicator of N deficiency in spring and winter wheat
Available soil N and a cultivars genetic potential are the primary factors determining grain protein concentration (GPC). Several studies have suggested that the close relationship between GPC and the amount of available soil N may allow GPC to be used as a post harvest indicator of growing season soil N deficiencies. The objective of this study was to determine if GPC was a practical indicator of crop N deficiencies in a wide range of wheat cultivars grown under the variable environmental conditions of western Canada. Wheat cultivars and lines representing quality types and GPC ranging from low protein soft white through Canada Prairie Spring and hard red winter to high protein hard red spring were grown in a total of 16 N fertilizer trials on dryland at Saskatoon, Clair and Yorkton and partial irrigation at Saskatoon from 1992 to 1998. Two methods were used to determine GPC at maximum grain yield and 90 and 80 percent of maximum grain yield. Both genotype and environment influenced the upper limit of yield when N was not limiting. While variation amongst cultivars tended to be smaller within market classes, it was large enough to suggest that the critical GPC-grain yield responses must be know for each cultivar before GPC can be used as a practical post-harvest indicator of N sufficiency. Growing season weather conditions also had a large influence on GPC-grain yield relationships and as the potential grain yield of a cultivar was reduced by environmental limitations the GPC at the point of maximum grain yield increased. Similar GPC-grain yield relationships were found at 90 and 80 percent of maximum grain yield. These observations indicate that GPC may be a useful post-harvest indicator of N deficiencies for crops that are under high N stress but caution must be used when employing GPC to develop management systems that optimize N fertilizer use.
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