Nitrogen efficiency of wheat: Genotypic and environmental variation and prospects for improvement

Abstract

Winter wheat (Triticum aestivum L.) was grown for 4 years in multi-factorial field trials at Rothamsted, southern England. Thirty nine elite commercial cultivars (primarily short-straw) were grown including those released in the UK over a 25-year period, a selection of continental varieties, and three older, tall varieties. Varieties spanned the quality spectrum from 'bread' to 'feed'. The crops were given ammonium nitrate at five rates in the range 0-350 kg-N/ha as a 3-way split. The aim was to quantify the genotypic variation in total nitrogen uptake by grain and straw (total-Nup), and in nitrogen utilization efficiency for grain yield (grain yield per unit of N taken up) (grain-NutE). Depending on treatment, grain yield ranged from 2.1 to 11.8 t/ha (85% DM), grain %N from 1.1% to 2.8% (in DM), total-Nup from 31 to 264 kg-N/ha, and grain-NutE from 27 to 77 kg-DM/kg-N. There were significant varietal differences in total N-uptake and grain-NutE both between 'tall' and 'short' varieties and within 'short' varieties. The best short varieties took up 31-38 kg/ha more N than the worst, and grain-NutE was 24-42% better, depending on N-rate. Up to 77% of the variation in grain-NutE was accounted for by yield. All interactions between the factors 'Variety', 'Year', and 'N-rate' were highly significant, but only 'Year × N-rate' made an important contribution to the variation. There was a near-functional inverse relationship between grain-NutE and grain %N; high-quality wheat (high grain %N) can be expected to have a low grain-NutE. The four key variables determining N-efficiency in a wheat crop-grain yield, grain %N, total N-uptake and nitrogen harvest index (NHI)-are ultimately constrained by the law of conservation of matter. Improving grain-NutE for fixed total-Nup and NHI can only be achieved at the expense of grain %N. To improve grain-NutE and maintain grain %N requires a simultaneous increase in NHI and grain starch yield which may be difficult to achieve in practice. The law of conservation of matter ultimately sets a limit on the physiological and agronomic processes that determine crop N requirements. A high yield of high-quality grain (high grain %N) requires a high input and uptake of nitrogen.

Characterization of brazilian wheat cultivars in terms of nitrogen use efficiency

“…Additionally, it was observed that genotypes with the lowest values of GPC were the same as those that showed high values of GY. This result corroborates other studies which have also reported negative associations between these traits (Barraclough et al, 2010;Monaghan et al, 2001).…”

“…The N concentration in the total biomass (NCB) ranged from 2.05% to 3.33% (Figure 4a), and agreeing with the reports of Barraclough et al (2010) and Haberle et al (2008) who found values of percentage of N in grains ranging from 1.52 to 2.87%. This trait was not influenced by an environmental component.…”

“…The genotype by environment interaction (G×E) was significant for all traits, except for harvest index (HI). These results are similar to those reported by Barraclough et al (2010), Haile et al (2012) and Suprayogi et al (2011). The coefficients of variation ranged from 2.0 to 7.4%, indicating high experimental precision.…”

“…In Pato Branco, the mean HI was slightly lower (0.43), whereas large values were observed for the cultivars CD 150, Marfim and, BRS Guamirim. Barraclough et al (2010) observed a higher variation of HI (0.37 to 0.76) than observed in this study.…”

“…Several studies indicate that the NUE of wheat is lower than 60%, and range from 31 to 264 kg N ha -1 (Barraclough et al, 2010;Haile et al, 2012). The presence of genetic variability for NUE have been reported in many countries such as Mexico (Ortiz-Monasterio et al, 1997), France (Górny et al, 2011), England (Foulkes et al, 2009) Argentina (Velasco et al, 2012), and Australia (Hochman et al, 2013).…”