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J.H. Mitchell, J. Challe, and S. Fukai

School of Land and Food, The University of Queensland, Brisbane, Queensland 4072.


The relationship between nitrogen application and grain yield and/or grain protein is complex. An experiment using 29 F6 progeny lines and the 2 parent lines was conducted to examine how assimilate and nitrogen availability at around anthesis determine grain yield and grain protein concentration. Nitrogen at anthesis significantly increased nitrogen uptake, grain yield and grain protein concentration while canopy exposure increased nitrogen uptake and grain yield but maintained grain protein concentration. Variation in nitrogen uptake accounted for between 49-84% of variation in grain yield while only accounting for between 0-32% of variation in grain protein concentration. No significant association existed between grain yield and grain protein concentration.

Production of a large quantity of acceptable quality grain is a major issue to both individual farmers and the barley industry as a whole. Barley is primarily grown for malting, and grain protein concentration (GPC) is a major quality factor that determines whether grain is classified as malting or feed barley. With the recent decline in soil fertility in barley growing areas, soil nitrogen (N) management for the sustainable production of high yielding crops of malting barley is important. Nitrogen and assimilate availability and hence GPC and grain yield (GY) is dependant on environmental conditions pre- and post-anthesis (1). This experiment was conducted to improve our understanding of the determinants of GPC in barley using progeny lines developed from a biparental cross.


This experiment was conducted between June and October 1996 at the University of Queensland Research Station, Redland Bay in south-east Queensland. The experiment examined genotypic variation for GY and GPC among 29 F6 lines from a Kaputar x Cameo cross (parent lines were included), in terms of response to N application and canopy exposure at anthesis. The control and canopy exposure treatments relied on residual soil N, with no application of N at planting. N application (100 kg/ha) and canopy exposure (removal of 2 border rows, leaving only 2 central rows) treatments were introduced at anthesis. Biomass harvests (16 plants) were sampled from the inner 2 rows at maturity.

Results and discussion

Treatment differences were significant for all attributes. N application at anthesis resulted in increased GY (Table 1). It is likely that less grain were aborted and photosynthetic capacity of plants were maintained through high N uptake. High N uptake resulted in excess N which was deposited in the grain and therefore a high GPC resulted. The effect of canopy opening at anthesis on GPC was negligible. With enhanced light interception, assimilate production was increased and resulted in improved GY but on average lines were able to maintain GPC. The removal of neighbouring plants may have resulted in more N becoming available to remaining plants and thus allowed for maintenance of GPC. However, Boonchoo et al.(1) conducted an experiment in which plants were not removed to achieve an open canopy treatment and canopy opening at anthesis tended to increase total N uptake, though the effect was not significant (p<0.05). Therefore, in this experiment the increased assimilate production may have increased demand for N, which was supplied by an increase in N uptake. The fact that similar GPC was maintained when assimilate availability was increased by canopy opening suggests that there is a minimum N concentration required for deposition of assimilate in the grain.

Within treatment, line variation for GY was significant when N was limiting but not when excess N was available, however significant differences existed in GPC only when N was ample. Combined analysis indicated treatment by line interaction effect was not significant but line variation was significant (P<0.05) for GPC, GY and N uptake (P=0.07). On average, GY and GPC of progeny lines was greater than parent lines, with a number of progeny lines achieving both high GY and high GPC due to high N uptake. Furthermore, no significant association existed between GY and GPC. This implies that there is scope to identify and select for higher yielding lines within the desired GPC range. Both GY and GPC were positively associated with N uptake, however GY to a greater extent. In the control and canopy exposure (N limiting) treatments, variation in N uptake accounted for 84% of variation in GY, while only accounting for 49% in the N application treatment. For GPC, variation in N uptake only accounted for 14 and 32%, respectively, in the N and canopy exposure treatments and the association was not significant in the control treatment.

GPC depends on both N and assimilate availability to grain, however, evidence suggests a minimum grain N concentration is maintained.

Table 1. Mean grain yield (GY, t/ha), nitrogen uptake (NU, kg/ha) and grain protein concentration (GPC, %) for 31 barley lines in three treatments and average across treatments. Genotypic variation is also indicated: * P<0.05; * * P<0.01; n.s., not significant at P=0.05.

total nitrogen uptake (kg/ha) for 31 lines in three treatments. Solid symbols represent parent lines.


1. Boonchoo, S., Fukai, S. and Hetherington S. 1998. Aust. J. Agric. Res. (In press)

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