**2. Nitrogen requirement and NUE**

Nitrogen is one of the nutrients plants need in high quantity [20], as it is a core constituent of a plant's nucleic acid, proteins, enzymes, and cell wall and pigment system [21]. The availability of nitrogen for plants is complex, and depending on different processes in connection with nitrogen cycle in the environment (**Figure 1**). Through the different way of nutrition supply and agrotechnology processes, the agriculture has a main impact on global and local nitrogen cycle. Plants also can have an effect on your own nitrogen supply by connecting different bacteria or releasing different extracts, like nitrification inhibitors. Biological nitrification inhibition (BNI) is the natural ability of certain plant species to release nitrification inhibitors from their roots that suppress nitrifier activity, thus reducing soil nitrification and N2 O emission (**Figure 1**). Among the tropical pasture grasses, the BNI function is the strongest in *Brachiaria* sp. [22].

Wheat Sensitivity to Nitrogen Supply under Different Climatic Conditions http://dx.doi.org/10.5772/intechopen.76154 33

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

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

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

Nitrogen is one of the nutrients plants need in high quantity [20], as it is a core constituent of a plant's nucleic acid, proteins, enzymes, and cell wall and pigment system [21]. The availability of nitrogen for plants is complex, and depending on different processes in connection with nitrogen cycle in the environment (**Figure 1**). Through the different way of nutrition supply and agrotechnology processes, the agriculture has a main impact on global and local nitrogen cycle. Plants also can have an effect on your own nitrogen supply by connecting different bacteria or releasing different extracts, like nitrification inhibitors. Biological nitrification inhibition (BNI) is the natural ability of certain plant species to release nitrification inhibitors from their roots that suppress nitrifier activity, thus reducing soil nitrification and

O emission (**Figure 1**). Among the tropical pasture grasses, the BNI function is the strongest

of functional ingredients [2].

32 Global Wheat Production

unfavourable conditions.

N2

in *Brachiaria* sp. [22].

**2. Nitrogen requirement and NUE**

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 NRE than the stem and the roots [33]. About 70–80% of nitrogen, which is needed for grain development in cereals, is gained from vegetative organs before flowering stage [34]. Nitrogen use efficiency (NUE) plays a fundamental role in sustainable grain production [35, 36]. Based on several physiological parameters of doubled-haploid mapping wheat populations can lead to identification of specific loci that might be useful in marker-assisted breeding for increased N-use efficiency [35, 37, 38].

influenced plant water status by reducing the water potential and the relative water content in wheat [51]. Optimal nutrition levels have also alleviated drought stress damage by sustaining metabolic activities under reduced tissue water potential [52]. Nitrogen supply also has a crucial role in combating drought [53]. Efficiency of nitrogen supply declined with increasing of drought stress [54]. Morgan [55], Arun et al. [56] and Binghua et al. [57] who showed that with an application of nitrogen, plants show positive influence in terms of growth and development under drought stress. Although Li et al. [58] mentioned that different grass species under drought stress did not modify physiological functions under varying N application. Water limitation reduces diffusive conductivity which in turn affects other physiological process such as energy and N metabolism. It is concluded that N uptake and its diffusion depend on environmental condition especially to water supply as also indicated by Abreau et al. [59]. Under water deficiency, roots are unable to get optimal amounts of nitrogen from soil, which has general negative effects on plant metabolisms [60]. The main effect of water restriction is certainly a reduction in N demand due to the marked sensitivity of leaf area expansion [61]. Fewer results have about light reaction affected by genotypic and nitrogen supply variations, mainly under stress conditions. By measuring the yield of chlorophyll fluorescence (Chl-fl), information about changes in the efficiency of photochemistry and heat dissipation can be obtained [62]. Under extreme drought stress when the stomatal resistance just around 0.1 mol

Wheat Sensitivity to Nitrogen Supply under Different Climatic Conditions

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

35

assimilating enzymes such as Rubisco become the dominant limitations to reduced photo-

tigated two environmental factors, and genotype differences were established in tolerance [64]. Chl-fl parameter's sensitivity for detecting nitrogen deficiency is different, but some of them are really applicable for describing nitrogen lack [65]. Previous drought stress studies have reported that photosynthetic rate of the leaf under drought stress is closely related to the leaf chlorophyll contents, N concentrations and stay-green characteristics of the leaf, which in turn increases the grain yield by increasing the photosynthetic process [66]. Palta et al. [67] and Hosenlou et al. [54] reported induction of N remobilisation under drought stress. Application of the high amounts of N under drought resulted to the lowest NUE [68]. Critical, sufficient concentration of nitrogen in leaf is 15–40 mg g−1 DM [69]. Based on Pepó [16] and Zsombik and Seres [70] results, the dry weight production was mainly influenced by environmental factors and modified by fertilisers and genotypes. Water deprivation means higher strain than nitrogen luck with genotype difference based on dry weight value [65]. Plant responses to drought stress vary at different growth stages of the crop [71]. In wheat, tillering capacity of the crop is a major constituent of the final grain yield [72], but has been

Salinisation or increased concentration of dissolved cations/anions in soil solution and/or water resources (e.g. capillary rising of saline groundwater, salinised waters used for irrigation) [74] across the (agro)ecosystems is the principal cause of most widespread abiotic constraint to glycophytes (i.e. the majority of cultivated crops, including wheat) known as salt

/Fm) and downregulated activities of CO2

/Fm) values were sensitive for the inves-

H2

O m−2 s−1, poor performance of photosystem II (Fv

synthesis [63]. The optimal photochemical activity (Fv

reported to be highly vulnerable to drought stress [73].

**5. Salinisation and impact to wheat production**
