JXB Advance Access originally published online on April 23, 2009
Journal of Experimental Botany 2009 60(7):1939-1951; doi:10.1093/jxb/erp116
REVIEW-ARTICLE |
Analysing nitrogen responses of cereals to prioritize routes to the improvement of nitrogen use efficiency
ADAS Boxworth, Cambridge CB23 4NN, UK
* To whom correspondence should be addressed. E-mail: Roger.Sylvester-Bradley{at}adas.co.uk
The efficient use of fertilizer nitrogen (N) is crucial to sustainable human nutrition. All crops receive significant amounts of additional N in temperate environments, through fixation or fertilizer use. This paper reviews progress towards the efficient use of fertilizer N by winter wheat (Triticum aesitivum L.) and spring barley (Hordeum vulgare L.) in the UK, acknowledging that on-farm this is governed by economics. Recent multi-site N response experiments on old and modern varieties show that yield improvements since the 1980s have been accompanied by increases in economic optimum N amounts for wheat but not for spring barley. On-farm N use efficiency (NUE) has increased for barley because increased yields with optimum N were associated with compensatory decreases in grain N concentration, whereas on-farm NUE has not increased for wheat because grain N concentration has not changed and improvements in N capture were insufficient to make up for the increased yield. Genetic effects on NUE are shown to differ markedly depending on whether they are determined at a single N rate, as in variety trials, or with optimum N amounts. It is suggested that, in order to elicit faster improvement in NUE on farms, breeding and variety testing should be conducted at some sites with more than one level of applied N, and that grain N%, N harvest index, and perhaps canopy N ratio (kg N ha–1 green area) should be measured more widely. It is also suggested that, instead of using empirical functions, N responses might be analysed more effectively using functions based on explanations of yield determination for which the parameters have some physiological meaning.
Key words: Barley, improvement, nitrogen use efficiency, optimum nitrogen, wheat
Received 24 October 2008; Revised 17 March 2009 Accepted 18 March 2009