Abstract
The purpose of this study is to focus on the nitrogen balance and losses in agricultural system. The influence of precipitation, irrigation and fertilizer application on some soil parameters, N-uptake by plant production and N-output by lysimetric water are evaluated in this paper.The study is carried out on Fluvisol, near Plovdiv in Southern Bulgaria under the conditions of field experiments with different vegetable crops (eggplant, green beans and carrots) over the period 2009-2011. The experimental design includes 3 treatments with nitrogen application –N0, N80 and N160 on the background of P80K80 kg.ha-1. The field plots are equipped with modification of Ebermayer type of lysimeters, which collect water from 100 cm depth of soil profile.According the received data it was observed that compensation between the amounts of N input and output was achieved in two variants (N80, N160) for all crops growing. Reducing the nitrogen input to the amount applied by precipitation and irrigation waters is the most ecological-friendly technological decision and very important factor for environment protection.

Keywords: Agricultural system, fertilization, nitrogen balance, nitrogen leaching, vegetables, environment protection

References

Addiscott, T. M., 1996. Measuring and modelling nitrogen leaching: parallel problems. Plant and Soil 181, 1-6.

Alexandrova, P., D.Donov, Stoicheva, D., 2001. Some ecological problems of Nitrogen fertilization by carrots growing, Journal of Soil Science, Agrochemisrty and Ecology 36(2-3): 85-88.

Alexandrova P., Koleva, V., Stoicheva, D., Donov, D., 2007. Environmental aspects of the application of mineral fertilizers in the cultivation of eggplant, In: Proceedings from International Conference “60 years institute N.Pushkarov”, pp.509-513.

Alexandrova P., 2008., Uptake of nutrients in carrots according to the norms of fertilization. In: Proccedings from scientific conference with international partipation “The science in globalization condition”, Kardzhali, 22-26.

Arinushkina, E., 1970. Guidelines in Chemical Soil Analysis, Izd. MGU, Moskow, p. 487.

Barros R., Isidoro, D., Araguls, R., 2012. Irrigation management nitrogen fertilization and nitrogen losses in the return flows of la Violada irrigation district (Spain), Agriculture, Ecosystems & Environment 155: 161-171

Beaudoin, N., Saad, J.K., Van Laethem, C., Machet, J.M., Maucorps, J., Mary, B., 2005. Nitrate leaching in intensive agricultura in Northern France: Effect of farming practices, soils and crop rotations Agriculture, Ecosystems & Environment 111: 292–310.

Bordoloi L. J., Singh, A.K., Manoj-Kumar, Patiram, Hazarika, S., 2013. Evaluation of nitrogen availability indices and their relationship with plant response on acidic soils of India. Plant, Soil and Environment 59, pp. 235-240.

Candela L., K.J. Wallis, R.M. Mateos, 2008. Non-point pollution of groundwater from agricultural activities in Mediterranean Spain: the Balearic Islands case study , Environmental Geology, 54 (3), 587–595.

Directive 91/676/EEC of 12 December 1991. Concerning the protection of waters against pollution caused by nitrate from agricultural sources. European Councel, 1991.

Gauger, T., Koble, R., Spranger, T., Bleeker, A., Draaijers, G., 2001. Deposition loads of sulpher and nitrogen in Germany, Water, Air and Soil Polution 1 (1/2): 353-373.

Koleva, V., Stoicheva, D., 2002 . Leaching of nitrates and base cations under Fluvisoils in different crops growing and nitrogen rates, International Congress of European Soils, Book of Abstracts, Eds. W. H. Blum, M. H. Gerzabek and M. Vodrazka, Vienna, Austria, pp.289.

Koutev, V., Slavov, D., Filcheva, E., Rousseva, S., Stoicheva, D., Dimitrov, I., Borisov, P., Markov, E., 2006. Balance of nutrients and changes in fertility of Bulgarian soils. In: Proceedings on soil fertility and future of agriculture in Europe, Bucurest, Editor Terra Nostra, pp. 17-27.

Mitchell, M.J., 2011. Nitrate dynamics of forested watersheds spatial and temporal patterns in North America, Europe and Japan, Journal of Forest Research 16(5): 333-340.

Mitova, I., Alexandrova, P., Stoicheva, D., 2011., Influence of mineral fertilization on the uptake of Nitrogen with late field production of eggplant. In proceedings from International Conference “100 years soil science in Bulgaria”, part two, 582-586.

Mosier, A., Kroeze, C., Nevison, C., Oenema, O., Seitzingerm, S., van Cleamput, O., 1998. Closing the global N2O budget: Ni-trous oxide emissions through the agricultural nitrogen cycle. Nutrient Cycling in Agroecosystems 52: 225–248.

Oenema, O., Kros, H., de Vries, W., 2003. Approaches and uncertainties in nutrients budgets: implications for nutrient management and environmental policies. European Journal of Agronomy 20: 3–16.

Oborn, A.C. Edwards, E. Witter, O. Oenema, K. Ivarsson, P.J.A. Withers, S.I. Nilsson, A. , 2003. Richert Stinzing Element balances as a tool for sustainable nutrient management: a critical appraisal of their merits and limitations within an agronomic and environmental context. European Journal of Agronomy 20: 211–225.

Page, A.L., Miller, R.H.& Keeney, D.R. (Eds.), 1982. Methods of Soil Analysis, Part 2. Chemical and microbiological properties. 2ndedition , ASA and SSSA, Madison, Wisconsin, USA, p.1159.

Poch-Massegi R., Jimenez-Martinez, J., Wallis, K.J., Ramirez de Cartagena, F., Candela, L., 2014. Irrigation return flow and nitrate leaching under different crops and irrigation methods in Western Mediterranean weather conditions. Agricultural Water Management 134: 1-13.

Raikova, L., Stoichev, D., Angelov, G., Stoicheva, D., 1996. Testing of different ways of N-fertilizer application for decreasing the nitrate content in some vegetable crops, Van Cleemput et al.,(eds.), Progress in Nitrogen Cycling Studies, 265-270.

Roy, R.N., Misra R. V., 2005. Soil nitrogen balance assessment and its application for sustainable agriculture and environment. China Life Sciences 48 (S2):843-55.

Standard for drinking water, 1983. Governamental Agency on Standards and Metrology, Ministry of Environment and Waters- N 2823-83.

Shröder, J.J., Neeteson, J.J., 2006. Nitrogen management in agroecosystems in relation to the Water Framework Directive. In: Proceedings of the 14th N workshop, Wageningen, pp. 241–243.

Smith D.R., Livingston, S.J., Zuercher, B.W., Larose, M., Heathman, G.C., Huang, C. ,2003. Nutrient loss from row crop agriculture in Indiana, Journal of Soil and Water Conservation 63: 396–409.

Salo, T., Turtola, E., 2006. Nitrogen balance as an indicator of nitrogen leaching in Finland. Agriculture, Ecosystem and Environment 113 (1-4): 98-107.

Stoichev, D., 1974. A device to obtain lysimetric water. Soil Science and Agrochemistry 5: 13-18.

Stoicheva, D., Angelov, G., Raikova, L., Donov, D. Alexandrova, P., Stoichev, D. 1996. Effect of some N-fertilization practices on nitrate level in the plant-soil system. In: Transactions of the 9th Nitrogen Workshop, Braunschweig, Germany, pp. 449-452.

Stoichev, D., Marinova-Garvanska, S., Stoicheva, D., 1998. Balance of nitrogen at different land use variants, In: Conference proceeding “Nitrogen cycle and balance in Polish Agriculture”, Andrzej Sapek (ed.), Falenty, Poland, 1-2 December, 45-54.

Stoicheva, D., Alexandrova, P., Donov, D., Stoichev, D., Angelov, G., Raikova, L., 2002. Ecological assessment of different nitrogen fertilizer rates in a vegetable crop rotation, Bulgarian Journal of Agricultural Sciences 8: 141- 150.

Stoicheva, D., Alexandrova, P., Koleva, V., 2003. Effect of fertilizer application on the migration of chemical elements in Fluvisol, Journal of Balkan Ecology 6(2):161 - 168.

Stoicheva, D., Kercheva, M., Koleva, V., Alexandrova, P., Simeonova. Ts., 2008. Good agricultural practices for the protection of groundwater by nitrates pollution from agricultural practices. Sofia, Brochure, p. 32.

Stoicheva, D., Alexandrova, P., Koleva, V., Simeonova, Ts., Mitova, Iv.. Atanasova, E., 2011. Nitrogen balance in different vegetable crops growing on Fluvisol in Southern Bulgaria. In: Proceeding of International conference “100 years Bulgarian Soil Science”, 16-20 May, Sofia, p. 654-658.

Tilman D., Cassman, K.G., Matson, P.A., Naylor, R., Polasky, S., 2002. Agricultural sustainability and intensive production practices. Nature 418: 671–677.

Wallis K., Candela, J.L., Mateos, R.M., Tamohр, K., 2011. Simulation of nitrate leaching under potato crops in a Mediterranean area. Influence of frost prevention irrigation on nitrogen transport, Agricultural Water Management 98: 1629–1640.

Wang B., Liu, W., Xue, Q., Dang, T., Gao, C., Chen, J., Zhang, B., 2013. Soil water cycle and crop water use efficiency after long-term nitrogen fertilization in Loess Plateau. Plant, Soil and Environment 59: 1-7.