Diverse concepts of breeding for nitrogen use efficiency. A review

Abstract

Cropping systems require careful nitrogen (N) management to increase the sustainability of agricultural production. One important route towards enhanced sustainability is to increase nitrogen use efficiency. Improving nitrogen use efficiency encompasses increasing N uptake, N utilization efficiency, and N harvest index, each involving many crop physiological mechanisms and agronomic traits. Here, we review recent developments in cultural practices, cultivar choice, and breeding regarding nitrogen use efficiency. We add a comparative analysis of our own research on designing breeding strategies for nitrogen use efficiency in leafy and non-leafy vegetables, literature on breeding for nitrogen use efficiency in other vegetables (cabbage, cauliflower), and literature on breeding for nitrogen use efficiency in grain crops. We highlight traits that are generic across species, demonstrate how traits contributing to nitrogen use efficiency differ among crops, and show how cultural practice affects the relevance of these traits. Our review indicates that crops harvested in their early or late vegetative phase or reproductive phase differ in traits relevant to improve nitrogen use efficiency. Headforming crops (lettuce, cabbage) depend on the prolonged photosynthesis of outer leaves to provide the carbon sources for continued N supply and growth of the photosynthetically less active, younger inner leaves. Grain crops largely depend on prolonged N availability for uptake and on availability of N in stover for remobilization to the grains. Improving root performance is relevant for all crop types, but especially shortcycle vegetable crops benefit from early below-ground vigor. We conclude that there is sufficient genetic variation available among modern cultivars to further improve nitrogen use efficiency but that it requires integration of agronomy, crop physiology, and efficient selection strategies to make rapid progress in breeding. We also conclude that discriminative traits related to nitrogen use efficiency better express themselves under low input than under high input. However, testing under both low and high input can yield cultivars that are adapted to low-input conditions but also respond to high-input conditions. The benefits of increased nitrogen use efficiency through breeding are potentially large but realizing these benefits is challenged by the huge genotype-byenvironment interaction and the complex behavior of nitrogen in the cropping system.

Effect of Deprivation and Excessive Application of Nitrogen on Nitrogen Use Efficiency‐Related Traits Using Wheat Cultivars, Lines, and Landraces

“…The current study, as well as several others (Cormier et al, 2013;Mahjourimajd et al, 2016), suggested the need for a better definition for NUE due to the criticisms that have been reported for the initial NUE (calculated according to Moll et al, 1982) that focus only on productivity. Moreover, selecting genotypes for NUE using Moll's model could be misleading because it does not consider genotype efficiency under low N supply and response under high N supply (Lammerts van Bueren and Struik, 2017). Therefore, achieving the maximum NUE will be attained at the lowest N supply used, which will most likely be at the expense of productivity.…”

“…Therefore, achieving the maximum NUE will be attained at the lowest N supply used, which will most likely be at the expense of productivity. Moreover, selecting genotypes for NUE using Moll's model could be misleading because it does not consider genotype efficiency under low N supply and response under high N supply (Lammerts van Bueren and Struik, 2017). Also, NUE allocates most of the GY to the soil available N (which is difficult to estimate, especially as roots often grow deeper than the soil tested), and it does not consider any other N sources (i.e., mineralization of the organic matter, atmospheric N deposition, N in irrigation and rainwater; Cormier et al, 2013).…”

“…The N management practice improvement includes identifying the optimum N application rate, source, and the growth stage(s) to apply N (Dieckow et al, 2006;Megda et al, 2009). Interestingly, estimating N demand during crop growth based on the estimation of N in plant and soil is an excellent strategy to aid precision N fertilization (timing, quantity, and placing) (Lammerts van Bueren and Struik, 2017). However, this estimation is challenging, as it requires handling an open and unpredicted environmental condition (Tremblay et al, 2009) and is also subjected to substantial G ´ E interactions.…”

A plant’s inheritance : Soil legacy effects of crops and wild relatives in relation to plant functional traits

“…Moreover, a trait-based approach has been recommended for the study of plant-soil interactions and plant legacy effects (Bardgett, Mommer & De Vries 2014;Kardol et al 2015;Bardgett 2017), as well as agro-ecosystem functioning to inform sustainable management practices (Martin & Isaac 2015;Wood et al 2015;Lammerts van Bueren & Struik 2017). …”

“…Moreover, in agro-ecosystems there is ample scope to also study impacts of intra-specific trait variation and plant legacy effects as well (Philippot et al 2013;Milla et al 2015;Lammerts van Bueren & Struik 2017). For example, Brassica crop and cultivars vary in levels of secondary metabolites and their ability to suppress plant parasitic nematodes (Fourie et al 2016;Park et al 2017).…”