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

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

Wheat growth can be impaired by heat stress at any developmental stage, and modelling scenarios predict even warmer temperatures in the future [39]. Production of wheat is affected markedly by high temperature [40, 41]. Elevated temperature alters uptake and allocation of N, thus intensifying N deficiency in plants [42]. Wheat shows enormous diversity in canopy architecture, and it has long been proposed that optimised light distribution could improve radiation use efficiency as well as light interception [43]. In heat tolerance, the activ-

Therefore, increasing affinity would simultaneously improve adaptation to warmer condi-

tor of Rubisco is replaced from *L. gibertii* predicted increases of 12% in net assimilation [47]. Combined stress of high temperature and low nitrogen affected both the abundance and

According to the most recent assessment report of the Inter-governmental Panel on Climate Change, published in 2014, levels of anthropogenic emissions of greenhouse gases are now at their highest in history [49]. Agricultural production and its effect on land use are major sources of these emissions by sharing methane and nitrous oxide gases. Greenhouse gases causing air temperatures increase, thus more moisture evaporates from land and water bodies. Warmer temperatures also increase evaporation and evapotranspiration in plants, soils, and on other hand, they will also escalate the water stress frequency and intensity with a rise

Under dry conditions in the field, 75–100% of the grain yield could be attributed to stored assimilates, compared with 37–39% under high-rainfall conditions. Drought stress severely

 [45]. High temperature not only degrades Rubisco but also accelerates its inactivation by addition of inhibitory sugars to its active site. Moreover, Rubisco has a relatively low turnover number as compared with the other Calvin cycle enzymes. Activity of Rubisco is mainly regulated by a catalytic chaperone—Rubisco activase—which catalyses removal of inhibitory sugars from its active site, switching the enzyme to active mode [46]. Among cereals wheat's

decreases with temperatures [44].

species, in which it is achieved by concentrating

fixation and is one of the primary deter-

affinities. Models where wheat's substrate specificity fac-

increased N-use efficiency [35, 37, 38].

34 Global Wheat Production

**3. Temperature influence on nitrogen nutrition**

ity of enzymes has crucial role. Rubisco's affinity for CO<sup>2</sup>

mode of regulation of Rubisco, which catalyses CO2

**4. Effect of drought on wheat nutrition**

from 1 to 30% in acute drought land area by 2100 [50].

tions, the proof of concept coming from C4

Rubisco has one of the best CO2

minants of photosynthetic rate [48].

CO2

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 stress. Salt stress encompasses wide range of physiological dysfunctions as a consequence of primary salinity effects, that is, osmotic and ionic disorder. Primary salinity effects, depending on the salinity level/duration, crop/genotype type, development stage, and so on, very often cause different secondary salinity-induced effects such as reduced cell expansion and assimilate production (i.e. growth and yield reduction), production of reactive oxygen metabolites and even plant mortality [75]. The general salinity effects are quite visible and assume reduce biomass growth (shoot/root height and weight, leaf area) and changes in root and shoots colour (e.g. presence of leaf tip burns, scorching/firing of leaves) [76]. The extent to which growth and yield will be reduced under salt stress mostly depends on the salinity level and plant (crop) species (**Figure 2**).

growth parameters and grain yield can vary significantly among genotypes (**Figure 2**) and with the developmental stage at which salt stress occurs [75] as well under specific environmental conditions given that the interaction of crop (genotype) and environment is not com-

Environmental salinisation process represents an increasing environmental issue especially in intensive agroecosystems such as (fert)irrigated areas [83] but also in less intensive rain feed (semi)arid regions [84]. Salt-affected areas are often overlapping with numerous other physical, chemical and/or biological pedosphere constrains such as sandy soils with low water retention capacity, non-structured/dispersed (waterlogged) soils, organically depleted soils with diminished microbial activity/diversity and excessive alkalinity, specific ionic (Al, B) toxicity, and many other [84, 85] (**Figure 2**). Saline or alkaline (sodic) soils due to increased

/Mg2+) can be recognised and visually by crystallised (precipitated) salts on the soil surface (forming a brighter salt forms on the soil surface; **Figure 3a**) or at later (developed) stages by topsoil crusting, as a consequence of dispersed clay minerals and soil aggregates (**Figure 3b**). A constitute of structurally dispersed soils (e.g. clay particles, minerals, organics) undergo leaching through the soil profile, accumulating and blocking deeper macro/micro pores, especially in textured-heavier soil layers, and finally causing waterlogging (e.g. Burrow et al. [86]. Thus, salt-affected soils (profiles) depleted in adsorption matrices (organic matter and clay content notably) might be more prone to mobility and transfer of certain pollutants (e.g. toxic trace elements) on the soil/crop/groundwater routes, although certain genotypic differences

For instance, it was shown that raised soil solution salinity can significantly impact mobility of toxic Cd in the rhizosphere and enhance its uptake and root/shoot accumulation in different wheat cultivars [87, 88]. Also, sublimating the results of studies conducted by Norvell et al. [89], Khoshgoftarmanesh et al. [88] and Ozkutlu et al. [90] their outcomes suggest that

**Figure 3.** Topsoil (a) crystallisation of soluble salts (dotted brighter areas) in a wheat paddock, depleted with soil organic matter, and (b) crusting in an adjacent saline plot with disturbed soil structure (Esperance area, Western Australia).

, Ca2+, Mg2+ etc) and ionic interrelations (e.g. Na+

Wheat Sensitivity to Nitrogen Supply under Different Climatic Conditions

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

/Ca2+;

37

, Cl<sup>−</sup>

pletely understood but is likely to be significant [80].

**5.1. Salinisation and wider (agro)ecological impact**

concentration of particular slats (Na+

have to be considered.

Na+

Electrical conductivity (EC) is commonly used as an expression of the total dissolved salt concentration in an aqueous sample (e.g. water, soil solution) and usually express soil salinity level based on measured EC of saturated soil paste extracts (ECe ) (e.g. Rhoades et al. [77]). Therefore, ECe threshold level (i.e. ECt), as a numeric value at which crop growth and yield start to decline (more or less intensive under certain slope) can be very useful for categorisation of plants from salt tolerant (halophytes) to salt-sensitive (glycophytes) (**Figure 2**). In general, wheat is categorised as moderately tolerant to soil salinity (e.g. a threshold EC of 6.0 dS/m) [78] although existing significant differences among genotypes that it is difficult to make a categorical statement [79]. The relative effects of salt stress on wheat vegetative

**Figure 2.** Simplified presence of salt tolerance in some cereals (adapted according to Maas [81]). ECt represents the threshold in soil EC that is expected to cause the initial significant reduction in the maximum expected yield, whereas the slope is the percentage of yield expected to be reduced for each soil salinity unit above the ECt [82].

growth parameters and grain yield can vary significantly among genotypes (**Figure 2**) and with the developmental stage at which salt stress occurs [75] as well under specific environmental conditions given that the interaction of crop (genotype) and environment is not completely understood but is likely to be significant [80].
