**1. Introduction**

The global wheat consumption has escalated at a faster rate than all other cereals. This growth is accounted for by the increase in developing countries, mainly in China and India, and based on the future projection, the growth of wheat consumption will continue [1]. In these two countries, the use of production inputs, primarily nitrogen fertiliser and irrigation water, has risen dramatically as well. Wheat is an important staple crop, providing 20% of all calories

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

consumed by people worldwide. It is the leading source of non-animal protein in human food and also makes a significant contribution to animal feed. Increasing global demand for wheat is also based on the ability to make several food products and the increasing consumption of these with industrialisation. In particular, the properties of the gluten protein fraction allow the processing of wheat to produce bread, other baked goods, noodles and pasta, and a range of functional ingredients [2].

Beside the food demand sustainable nutrient supply and climatic effect on plant productivity are two crucial topics of agricultural development. Applying adequate amount of nutrients based on genotype requirements is hard under potential conditions, especially under different abiotic loads. Nitrogen (N) is an important nutrient, which determines the amount of yield and throughout the proteins the quality as well. The increased crop productivity has been associated with a 20-fold increase in the global use of nitrogen fertiliser during the 50 years [3], and this is expected to increase by threefold by the year 2050 [4]. Inadequate application of N—deficiency and excess—can cause environmental and ecological problems. Climatic factors can improve and deteriorate crop nutrient use efficiency and yield. Drought occurs in all climatic regions and drought-induced crop yield reduction is among the greatest losses in agriculture. About 32% of wheat production areas in developing countries experience serious drought stress in different growth stages [5]. Lobell et al. [6] published that climate trends were large enough in some countries to offset a significant portion of the increases in average yields that arose from technology, fertilisation, and other improving factors. High and low temperature [7–9], irrigation [10–12], salinisation [13, 14], agrotechnology [15–17], and other nutrients [18] also have an effect on N use of wheat. These effects are depending on the adaptation and acclimatisation strategies of different wheat genotypes, the current climatic conditions and its combinations and biotic effects as well [19]. To know more about and improve nitrogen use efficiency of wheat means a way towards the sustainability. Wheat being the basic food plant and the global demand for qualitative perfect food is increasing we have no other alternatives, than step forward to smart-wheat, which will be able to survive unfavourable conditions.

Nitrogen availability and using capacity are crucial in plant life. The chlorophyll content of wheat leaves and leaf N is closely related as the photosynthetic machinery accounts for more than half of the N in a leaf [24]. Nitrogen influences carbohydrate source size by leaf growth and leaf area duration and also the photosynthetic rate per unit leaf area and thereby source activity. The availability of N is of agricultural concern because plant metabolism is differently affected by excess, optimal and deficient levels [25]. The concept of nitrogen-use efficiency (NUE) has been widely used to characterise plant responses to different levels of N availability. Moll et al. [26] defined the most use of NUE, at least among breeders, which computes the grain dry mass divided by the total N available to a plant. It is divided into two components: NUE = NUpE × NUtE, where NUpE is the N-uptake efficiency calculated as the total amount of N in above-ground plant at harvest divided by the available N in soil, and NUtE is the utilisation efficiency calculated as the grain dry mass divided by the total amount of N in aboveground plant at harvest. Based on several authors, establishment N remobilisation efficiency (NRE) is also a main component of NUE [27]. The NRE—the proportion of N in the crop or crop component at anthesis which is not present in the crop or crop component at harvest—is the ability of plants to translocate the N after anthesis from the shoot to the grains. Nitrogen is the most limiting nutrient for the production of wheat [28]. Cultivars with higher NRE tend to accelerate the senescence process and increase N levels in grains [29]. It is widely understood that N accumulated before anthesis provides the major source of grain N. In wheat, around 50–95% of the grain N at harvest comes from the remobilisation of N stored in shoots and roots before anthesis [30–32]. In wheat between anthesis and maturity, the leaves had a higher

Wheat Sensitivity to Nitrogen Supply under Different Climatic Conditions

http://dx.doi.org/10.5772/intechopen.76154

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**Figure 1.** Nitrogen cycle (adapted according to LaRuffa et al. [23]).
