Crop Nitrogen Demand and Grain Protein Concentration of Spring and Winter Wheat

Goos et al., 1982). Selles and Zentner (2001) reported that a grain protein concentration of 12.8% was a reliAvailable soil N and a cultivar’s genetic potential are primary able indicator of N sufficiency in hard red spring (HRS) factors determining grain protein concentration (GPC). This study wheat grown in southwestern Saskatchewan. In confocused on important genotypic and environmental factors that determine GPC and yield potential in common wheat (Triticum aestivum trast, Fowler and Brydon (1989) reported that the N L.) and investigated the use of GPC as a practical indicator of crop requirements for maximum grain yield are normally met N deficiencies for a wide range of cultivars grown in 16 N fertilizer when the GPC–N response curve for Norstar winter trials in western Canada. Large GPC responses to added N were wheat reaches approximately 13% under average to accompanied by large increases in grain yield, and similar GPC–grain good weather conditions in Saskatchewan. Similarly, yield relationships were found at maximum grain yield and 90 and the critical GPC for spring wheat has been reported as 80% of maximum grain yield. Both genotype and environment influ13.5% for both the eastern prairies (Flaten and Racz, enced the upper limit of yield when N was not limiting. The relation1997) and Montana (Long and Engel, 1998). This wide ship between GPC and grain yield depended on the part of the N range of critical GPC values supports the conclusion fertilizer response curve sampled, and there was a strong negative drawn by Fowler et al. (1990) that there are important correlation between cultivar GPC and maximum potential grain yield. The latter observation indicates that the production of high-yielding differences in GPC–grain yield relationships that decultivars with high GPC is more complicated than simply stacking pend on production area (environment) and cereal speyield genes in a high-GPC genetic background or vice versa. Large cies and genotypes within species. differences amongst cultivars also suggested that the critical GPC– The objectives of this study were to quantify the imgrain yield responses must be known for each cultivar before GPC portant genotypic and environmental responses that decan be used as a practical postharvest indicator of N sufficiency. termine GPC and yield potential in common wheat and Growing season weather had a large influence on GPC–grain yield to determine if GPC can be used as a practical indicator relationships, and GPC at the point of maximum grain yield increased of crop N deficiencies grown under the variable environas the potential grain yield of a cultivar was reduced by environmental mental conditions of western Canada. limitations. These observations indicate that GPC may be a useful postharvest indicator of N deficiencies for crops that are under N stress, but caution must be used when employing GPC to develop MATERIALS AND METHODS management systems that optimize N fertilizer use. A total of 16 fertilizer trials consisting of five spring and five winter wheat cultivars representing the seven wheat quality classes of western Canada were grown on dryland at Saskatoon B a cultivar’s genetic potential and the environ(52 N, 107 W; Vertic Haploboroll soil), Clair (52 N, 104 W; Udic Haploboroll soils), and Yorkton (51 N, 102 W; Udic ment in which it is grown determine GPC. Nitrogen Haploboroll soils) and partial irrigation at Saskatoon from is the basic building block of protein, and as a conse1992 to 1998. The GPC of the wheat quality classes ranged quence, levels of soil available N have a large influence from low-protein soft white spring (SWS) and SWW through on GPC (Eilrich and Hageman, 1973). The large inCanada prairie spring red (CPSR) and white (CPSW) and creases in grain yield and GPC achieved with N fertilizahard red winter (HRW) to extra-strong spring (ESS) and hightion stand in sharp contrast to the negative correlation protein HRS. The cultivars used in these studies were selected that is normally observed between GPC and grain yield to represent the most highly adapted cultivars for these classes when only cultivar differences are considered. Therein this region. Additional data and new releases resulted in fore, the important role that N fertilizer management several cultivar changes over the course of this study. has to play in optimizing grain yields and the mainteTrials that included spring wheat were grown under partial irrigation at Saskatoon in 1992, 1993, 1994, 1995, 1996, 1997, nance of grain quality standards must be emphasized in and 1998 and on dryland at Saskatoon in 1996 and 1997 and efficient wheat production systems. Clair in 1996, 1997, and 1998. Trials that included winter wheat Several studies have suggested that the close relationwere grown under partial irrigation at Saskatoon in 1993, 1995, ship between GPC and the amount of available soil N 1997, and 1998 and on dryland at Saskatoon in 1997, Yorkton may allow GPC to be used as a postharvest indicator in 1997 and 1998, and at two locations at Clair in 1997. The of the adequacy of N management (Pierre et al., 1977; cultivars AC Reed, Katepwa, BW90, Roblin, and AC Taber Goos et al., 1982). The critical GPC for N sufficiency were included in the spring wheat trials starting in 1992. ‘Glenhas been reported to be 8.8% for Stephen’s soft white lea’ replaced BW90 in 1995, ‘AC Barrie’ was substituted for winter (SWW) wheat grown in Oregon (Glenn et al., Roblin in 1997, and ‘AC Vista’ replaced AC Reed in 1998. 1985) and between 11.1 and 12.0% for dryland winter ‘CDC Ptarmigan’, ‘CDC Kestrel’, S86-101, ‘Norstar’, and ‘Winalta’ were included in all winter wheat trials up to 1996 and wheat produced on summer fallow in eastern Colorado in Saskatoon and Clair dryland trials in 1997. The winter wheat Crop Dev. Cent., Univ. of Saskatchewan, Saskatoon, SK, S7N 5A8, Abbreviations: CPSR, Canadian prairie spring red; CPSW, Canadian Canada. Received 15 Apr. 2002. *Corresponding author (Brian. prairie spring white; GPC, grain protein concentration; HRS, hard Fowler@usask.ca). red spring; HRW, hard red winter; ESS, extra-strong spring; SWS, soft white spring; SWW, soft white winter. Published in Agron. J. 95:260–265 (2003).