Effects of long-term fertilization on the yield of winter wheat and N forms on Luvic Phaeosem soil determined in 0.01 MCaCl2

The effects of regular NPK fertilization on the amounts of winter wheat yield and the amounts and proportion of different N forms (NO ₃ -N, NH ₄ -N, N _org , N _total) of a Luvic Phaeosem soil determined in 0.01 <i>M</i> CaCl ₂ were studied in the B1740 variant of the National Long-Term Fertilization Experiment at Karcag. According to the yield data, N and P fertilization increased winter wheat yield significantly. When applying the 200 kg N·ha ^-1 dose, P fertilization resulted in a more than 2 t·ha ^-1 yield increase, as compared to the treatments without P fertilization. K fertilization had no effect on the yield, similarly to preceding years. These findings may be adapted to fields of the Middle-Tisza Region with similar conditions to the trial site. The N forms of the soil determined in CaCl ₂ reflected fertilization well. All of the fractions, but especially NO ₃ -N and N _total , increased significantly in response to N fertilization. Close relationships (r = 0.87–0.88) were found among the NO ₃ -N and N _total fractions and the N balance, which means that the amounts of NO ₃ -N and N _total are suitable for assessing both the N deficit and the N surplus. The strength of the correlation between the NH ₄ -N content and N balance was moderate (r = 0.65). The N _org fraction increased significantly as a function of N and P fertilization. These results can be explained with the yield increase. A significant correlation (r = 0.55) was found between the N _org fraction and yield amounts. It can be established that organic residuals remaining on the site resulted in a significant increase in the N _org content of soils. The gained results confirm that the N _org fraction is suitable for the characterization of the readily mobilizable N reserves previously ignored in fertilization practice. On the basis of the presented results the CaCl ₂ method is recommended for the precise estimation of nutrient requirements.