Effect of nitrogen from different sources on yield and quality of sugar beet in nitrate vulnerable zones

The impact of different forms and doses of nitrogen fertilization on quantitative and qualitative parameters of sugar beet was studied at Trnava hilly region (western part of the Slovak Republic) during 1998-2002 years with the aim to design environmentally friendly growing practices. Intera variety was grown in alfalfa - winter wheat - sugar beet crop sequences on fertile haplic Chernozems in an extremely dry climatic region. The sugar beet yield, digestion, potassium, sodium and a-amino-nitrogen were studied. Refined sugar extraction, refined sugar production and production of polarised sugar were also calculated. The average yield of beet (64.45 t per ha) varied from 47.64 tons in 2000 to 75.70 t per ha in 1999. Significantly lower digestion was reached in the variant FYM+NPK under a farm-yard manure combined with nitrogen mineral fertilization (15.03 deg S) and single manure application (15.06 deg S) in comparison with incorporated forecrop straw procedure (16.00 deg S). Digestion of beet was significantly influenced by weather conditions, fertilization and by the interaction of weather with fertilization. Average production of polarised sugar was 10.00 t per ha with the interval from 7.86 t per ha in 2000 to 12.17 t per ha in 1999. The main source of variability was weather and nitrogen input. Refined sugar extraction ranged from 10.66% in 1998 to 13.34% in 2000 with the total average of 12.48%. The variability of refined sugar extraction was highly significantly influenced by weather and nitrogen input and their interaction. Average refined sugar production was 7.83 t per ha with the interval from 6.38 t per ha in 2000 to 9.71 t per ha in 1999. Production of refined sugar was higher in the treatment with straw ploughing in (7.84 t per ha) as compared to the farm-yard manure application (7.22 t per ha). The application of straw instead of manure in analogues treatments caused significant (straw vs. manure) and highly significant (straw plus N-fertilizer vs. manure plus N-fertilizer) decrease of a-amino-nitrogen content in beet. The farm-yard manure application to sugar beet increases alpha-amino-nitrogen what concurrently decreases digestion, refined sugar production and refined sugar extraction. Excluding farm-yard manure application or decreasing nitrogen input in given agrochemical conditions on fertile soils increased qualitative parameters of sugar beet by acceptable production parameters and simultaneously decreased risk potential of water pollution by nitrates in arable soil ecosystem.