The critical crop nitrogen uptake is defined as the minimum nitrogen uptake necessary to achieve maximum biomass accumulation (W). Across a range of crops, the critical N uptake is related to W by a power function with a coefficient less than unity that suggests crop N uptake is co-regulated by both soil N supply and biomass accumulation. However, crop N demand is also often linearly related to the expansion of the leaf area index (LAI) during the vegetative growth period. This suggests that crop N demand could be also linked with LAI extension. In this paper, we develop theory to combine these two concepts within a common framework. The aim of this paper is to determine whether generic relationships between N uptake, biomass accumulation, and LAI expansion could be identified that would be robust across both species and environment types. To that end, we used the framework to analyze data on a range of species, including C3 and C4 ones and mono- and di-cotyledonous crops. All crops were grown in either temperate or tropical and subtropical environments without limitations on N supply. The relationship between N uptake and biomass was more robust, across environment types, than the relationship of LAI with biomass. In general, C3 species had a higher N uptake per unit biomass than C4 species, whereas dicotyledonous species tended to have higher LAI per unit biomass than monocotyledonous ones. Species differences in N uptake per unit biomass were partly associated with differences in LAI and N-partitioning. Consequently the critical leaf-N uptake per unit LAI (specific leaf nitrogen, SLN) was relatively constant across species at 1.8–2.0 g m−2, a value that was close to published data on the critical SLN of new leaves at the top of the canopy. Our results indicate that critical N uptake curves as a function of biomass accumulation may provide a robust platform for simulating N uptake of a species. However, if crop simulation models are to capture the genotypic and environmental control of crop N dynamics in a physiologically functional manner, plant growth has to be considered as the sum of a metabolic (e.g. leaves) and a structural (e.g. stems) compartment, each with its own demand for metabolic and structural N.
[Show abstract][Hide abstract] ABSTRACT: In the last 40 years, the global use of mineral N fertilizers has increased to support increasing food demand. Misuse of fertilizer has led to environmental problems in some regions and the rarefaction of energy leads to an increasing cost of mineral N fertilizers. For these reasons, improving N-use efficiency of crops and cropping systems is becoming a real challenge to growers, agronomists and breeders. Nitrogen-use efficiency depends on agronomic practices including mineral and organic nitrogen fertilization and the use of legumes in cropping systems, and genetic progress in nitrogen-use efficiency. The objective of this chapter is to develop a framework of the principles governing regulation of N uptake, N allocation and growth of plants and crops, and to apply these principles in tools for improving fertilization management and breeding. A theoretical analysis of the dynamics of plant and crop N demand in relation to growth potential during the crop cycle is developed. Agronomical tools to evaluate nitrogen status of plants and crops are presented and discussed. Physiological and morphological responses of plants and crops to N deficiency are then examined. Finally, the concept of nitrogen-use efficiency is considered in the light of the principles developed previously, and avenues for improving nitrogen-use efficiency through plant breeding and agronomy are discussed from a crop physiology point of view.
CROP PHYSIOLOGY - APPLICATIONS FOR GENETIC IMPROVEMENT AND AGRONOMY, 2nd edited by Victor O. Sadras, Daniel F. Calderini, 12/2015: chapter 8: pages 161-206; Academic Press, Elsevier.
"As reported in the literature, that N plays a key role in the plant vegetative growth (Lemaire et al., 2007). The increased N might have delayed inflorescences over control treatment at every next increase in N rate (Jin et al., 2012). "
"The parameters of Eq. (B6) have been determined for many species (Table 1). The value of allometric coefficient a has been approached by Lemaire et al. (2007) on the assumption that the metabolic compartment W m scales with the leaf area index (LAI) of the canopy: "
[Show abstract][Hide abstract] ABSTRACT: The nitrogen economy of the crop is a critical driver of biomass and grain production, and its importance is reflected in a large, worldwide research effort to link nitrogen, growth and yield. Particular research questions require measurement of specific traits, hence the need to quantify multiple, often complementary traits including crop nitrogen uptake, nitrogen use efficiency and its components, nitrogen concentration in the crop and its parts, down to relevant enzymes (e.g. nitrate reductase) and other products of gene expression. Nitrogen uptake, however, is co-regulated by both soil nitrogen availability and crop biomass accumulation; hence, crop nitrogen uptake or shoot nitrogen concentration reflect univocally crop nitrogen status only if comparisons are made at similar biomass. Although the allometric relationships between biomass and nitrogen uptake have been established for over two decades, many studies still report results in terms of nominal treatments, e.g. high vs low nitrogen, which are uninformative; curves relating yield and fertiliser rate, which are of local interest but provide little insight on the underlying processes and have low generic value; and nitrogen-related traits that are incomplete or inadequate to quantify crop nutrition status. Often, the allometric relationships between nitrogen and biomass are overlooked.
In this opinion paper, we summarise the already well established concepts of dilution curves and nitrogen nutrition index, outline the standard partitioning of nitrogen use efficiency, and highlight the confounded effects in nitrogen use efficiency when the allometric relationship between nitrogen uptake and biomass is ignored. A sample of recent papers is used to survey the most common approaches to characterise nitrogen related traits. We illustrate the application of dilution curves and nitrogen nutrition index in the assessment and interpretation of crop responses to agronomic practices and comparisons of wheat cultivars and maize hybrids.
Field Crops Research 08/2014; 164(1):54–64. DOI:10.1016/j.fcr.2014.05.006 · 2.98 Impact Factor
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