INTERNATIONAL CONGRESS OF ECOLOGISTS ECOLOGICAL SPECTRUM 2012 1103 NatašaČereković 1 UDK 502.175:[504.5:663.11 Sretenka Marković 2 NITROGEN AND WHEAT ABSTRACT The high yields of today s modern wheat cultivars require of the high input which leads to both higher production costs and a greater risk of environmental pollution. Nitrogen is a primary driver of crop production. Given sample sunlight and water and favorable temperatures, yields of dry substance and grain are loosely linked to the availability and uptake of nitrogen. Identifying traits to improve the nitrogen economy of wheat: recent advances and future prospects were studied by Foulkes and colleagues making an assessment of the role of nitrogen in wheat production. Key words: wheat, production, nitrogen, environmental pollution 1. INTRODUCTION The new varieties and favourable production economics encouraged the excessive use of fertilizers with consequences for the environment and growing consumer demand for healthier product. The most important for a plant growth is availability of water for plant and nutrients, where nitrogen is among one. The new breeding programmes are working a lot on drought resistance and efficient use of nutrient, as such an unfavourable growing condition leads to growth reduction and it is caused by decrease in stomatal conductance, CO 2 uptake, N uptake and accumulation in dry soils (Chaves 2003). 1 University of Aarhus, Faculty of Science and Technology, Department of Food Science, Kirstinebjergvej 10, Aarslev Denmark, e-mail: Natasa.Cerekovic@agrsci.dk 2 University of Banja Luka, Faculty of Agriculture, Bulevar vojvode Petra Bojovića 1, Banja Luka, Bosnia and Herzegovina, e-mail: sretenka25@yahoo.com
1104 N. Čereković, S. Marković: NITROGEN AND WHEAT To address this problem, the challenge is to maintain or improve productivity and profits with reduced inputs; basically to farm more cleanly and efficiently. Both molecular engineering and traditional plant breeding could be employed to produce plants better able to cope with the various processes limiting plant growth in elevated CO 2 environments. In contrast, the yield increments registered by the new wheat cultivars during this period have been bolstered by progressively higher N-inputs (Raun et Johnson, 1999). Plant breeding to environment is a long term proposition which a decade and even more time that can from the initial crosses need, bring a new suitable cultivar. It is very important to test all hybrid combinations over the years, and different environmental conditions in order to be sure that new cultivar can be suitable and perform well, both, for farmers and the consumers. All that has led to the idea that modern cultivars selected under conditions of high N-input are little suited to low-input conditions with respect to old wheat populations and cultivars. In the figure (Fig. 1), an input and losses of nitrogen in the environment is presented. Moreover, moving nitrogen through the soil system and plant was showed with final nitrogen in a yield in a moment of plant harvest. Fig. 1. Nitrogen in plants and environment (Good et al., 2004)
INTERNATIONAL CONGRESS OF ECOLOGISTS ECOLOGICAL SPECTRUM 2012 1105 Nitrogen use efficiency Nitrogen is one of the most expensive nutrients to supply, and may also have an environmental impact through nitrate leaching. The development of N- efficient cultivars will be of economic benefit to farmers and will help to reduce environmental contaminations associated with excessive inputs of N fertilizers. NUE (Moll et al., 1982) is a nitrogen use efficiency and grain dry substance yield per unit of N available (from the soil and/or fertilizer) and divided it into N-uptake efficiency (crop N uptake/n available) and N-utilization efficiency (grain dry matter yield/crop N uptake). The nitrogen economy of wheat is considered in relation to both NUE and the relationships between the grain protein content and composition and N supply. Environmental impact of nitrogen Despite the rapid increase of the yield with a great increase of human production of nitrogen fertilizers for agricultural production, an increase and evidence of detrimental effects for higher amount of reactive nitrogen in environment showed up. (Vitousek, 1997; Howarth, 2004;). The major environmental problems are acidification of the soil and water resources, surface and groundwater contamination, increase of an ozone depletion and crop injury, greenhouse gas levels due to N2O emission, loss of biodiversity in ecosystems, an invasion of N loving weeds, increased atmospheric haze and production of airborne particulate substance have developed due to the presence of excessive environmental N (Galloway et al., 2002). In the future, we can expect that water resources for irrigation become increasingly scarce, and fertilizer costs can increase together with costs of all agricultural inputs. Genetic variation in efficient use of nutrient has been showed in a large number of plants (Hirel et al. 2007; Foulkes et al. 2009). Increasing N content in a plant can improve nitrogen use efficiency under drought period and with that the nitrogen uptake efficiency and leaf nitrogen are both breeding targets for optimizing a yield. Management strategies for high NUE from the review paper by Foulkes and collegues In their study, the authors (Foulkes et al., 2010) present the view that the nitrogen fertilizer represents a significant cost of production for the grower one and may also have environmental impacts through nitrate leaching pollution of
1106 N. Čereković, S. Marković: NITROGEN AND WHEAT ground water, eutrification of rivers and lakes and global warming, use of fossil fuels for manufacture and application, and nitrous oxide emissions associated with denitrification by soil bacteria. The development of N-efficient cultivars will be of economic benefit to farmers and will help to reduce environmental contamination associated with excessive inputs of N fertilizers. In a review, work on nutrient use efficiency (Raun et Johnson, 1999) has been identified that only a 33 % efficiency was in cereal production for fertilizer N. From the economical point, and if the costs of natural gas increase, there will be causes for poor NUE. There are several factors that have influenced nitrogen use efficiency (Raun et Johnson, 1999) as a source of nitrogen, the method of application for fertilizer, cropping field system and pathways of N loss from the soil-plant system. Fertilizer-N management takes into account all natural processes responsible for N loss and present in the system. Promising N management strategies for high NUE should be considered (Foulkes., 2010) from the cellular to the whole-crop scale, including root traits with increasing root length density (RLD), high capacity for N assimilation in the stem, potentially associated with the maximum N uptake rate, leaf and canopy photosynthesis, more efficient post-anthesis remobilization of N from stems to grain, but less efficient remobilization of N from leaves to grain, both potentially associated with delayed senescence, a reduced grain N concentration may be of particular value for increasing NUE in feed wheat cultivars and for bread-making cultivars, high NUE may be associated with high capacities for uptake and assimilation of N, with high post-anthesis N remobilization efficiency and/or specific grain protein composition (Fig. 2). Fig. 2. Management strategies for high nitrogen use efficiency (Foulkes et al., 2010)
INTERNATIONAL CONGRESS OF ECOLOGISTS ECOLOGICAL SPECTRUM 2012 1107 Genetic breeding to improve NUE Improvement of traits by breeding will require studies to identify the genes underlying the key traits, and identify superior alleles under the low and high N conditions and to develop molecular markers to allow these to be selected in breeding programmes. The embryo and outer layers of the grain (including the aleurone) contain about 30% of the total grain N (Shewry et Halford, 2002). They are enriched in albumins, globulins and insoluble proteins, most of which are structural and metabolic in function, but both tissues also store a 7S globulin protein. Structural and metabolic proteins are also present in the starchy endosperm cells, but the predominant protein fraction in this tissue is the gluten storage proteins, comprising a mixture of monomeric gliadins and polymeric glutenins. These groups of proteins are present in approximately equal amounts and together account for about 60 70% of the total N in the endosperm tissue. The gluten proteins are crucial for the processing of wheat into bread, other baked food, pasta and noodles, as they confer viscoelastic properties to dough. A precise balance of gliadin and glutenin proteins is also required, as glutenins are predominantly responsible for dough elasticity (strength) and gliadins for dough viscosity and extensibility. Thus, highly elastic (strong) doughs are required for bread making and more extensible dough for making biscuits and cakes. Cultivars for bread making are selected for high protein content and strong gluten properties with the appropriate levels of N fertilizer being applied to the crop to ensure that the required protein content is achieved. The most effective way to modify grain protein amount would be to manipulate the amount of N transported into the grain. An alternative approach to producing high protein wheats for bread making is to improve the protein quality to increase the dough strength, allowing lower protein grain to be used for bread making. 2. CONCLUSIONS Using a nitrogen fertilizer in agricultural production increases a cost, and can have an effect of nitrogen leaching in the soil. The long-term effects of management practices on soil quality will also have an important influence on the NUE of the entire agroecosystem. Soil organic substance content is a key measure of the soil quality and soils that sequester carbon also sequester N, resulting in a greater indigenous N supply and a reduction in N fertilizer requirements.
1108 N. Čereković, S. Marković: NITROGEN AND WHEAT Therefore, management practices which increase soil organic substance will generally provide efficiency benefits over the long term. The better the agronomic basis of NUE is understood, the more likely is that the breeding strategies designed to rise productivity will be applied efficiently. In other words, the future progress will depend on integrating expertise from the whole plant molecular physiology approaches to breeding and agronomy to aid understanding of the regulation of N uptake, N assimilation and N recycling and remobilization in the different plant organs through growth and development under contrasting N levels. Such integrated studies will require the input from computer scientists and bioformaticians and crop, (Ritchie et Otter, 1985; Asseng et al., 2001; Jamieson et Semenov, 2000) as well as the development of large populations segregating for target traits. In particular, it will be important to increase the understanding of the extent to which the genetic control of pre-anthesis N accumulation and post-anthesis N remobilization is intrinsically linked, and whether there is an independent genetic control of these processes in the different plant organs. Future progress will depend on identifying traits at the biochemical, cellular and plant level and integrating towards field performance. 3. REFERENCES 1. Asseng, S., Turner, N. C., Keating, B.: Analysis of water and nitrogen-use efficiency of wheat in a Mediterranean climate. Plant Soil n.233, 2001, pp 127 143. 2. Barraclough, P. B., Howarth, J. R., Jones, J., Lopez-Bellido, R., Parmar, S., Shepherd, C. E., Hawkesford, M. J.: Nitrogen efficiency of wheat: Genotypic and environmental variation and prospects for improvement. European Journal of Agronomy n.33, 2010, pp 1 11. 3. Chaves, M. M., Maroco, J. P., Pereira, J. S.: Understanding plant responses to drought: from genes to the whole plant. Functional Plant Biology 30, 2003, 239 264. 4. Foulkes, M. J., Hawkesford, M. J., Barraclough, P. B., Holdsworth, M. J., Kerr, S., Kightley, S., Shewry, P. R.:,,Identifying traits to improve the nitrogen economy of wheat: Recent advances and future prospects,. Field Crops Research, n. 114, 2010, pp 329 342. 5. Galloway, J. N., Cowling, E. B.: Reactive nitrogen and world: 200 years of change. AMBIO: A Journal of the Human Environment 31, 2002, pp 64-71.
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