The effect of N-min. content in the soil profile on the yield and protein content in spring wheat grain | Wpływ zawartości N-min. w profilu glebowym na plon i zawartość białka w ziarnie pszenicy jarej

polonais. The field experiments were carried out in 2001–2003 on degraded chernozem developed from loess. These experiments studied the effects of stubble catch crop management on the accumulation of soil mineral N and N-NO3 leaching during winter, and the content of N-min. on the yield and grain quality of cv. Torka or Histra. The soil for mineral nitrogen form determination was sampled from three layers at the following dates: 1st 10 days’ period of November and March, 2nd 10 days’ period of May and 3rd 10 days’ period of June in the 0-90 cm soil profile depth. N-NO3 and N-NH4 content in the soil filtrate were determined using ionometric method on fresh or frozen samples. The grain yield of spring wheat and total protein content were higher after stubble catch crop (oleiferous radish). Catch crop residue management did not differ the grain yield and total protein of spring wheat. Nitrogen fertilization applied before sowing proved to have more favourable effects on the yield and total protein content of spring wheat. The content of nitrate-N depended on the sampling date and the depth of soil layer. The lowest content of N-NO3 was noticed in the 60-90 cm layer in comparison with the arable layer soil. In early spring the soil collected from the deepest layer revealed high nitrate-N content. Oleiferous radish cultivated caused a significant decrease of nitrogen in the first half of November as compared to the site without catch crop. However, at the beginning of May and June, due to mineralisation of ploughed radish biomass, N-min. content was higher on the site after catch crop compared to bare fallow. Nitrogen release from catch crop plant residues incorporated with soil before winter was higher only at the beginning of spring than from residues left on the surface. The efficiency of spring nitrogen fertilization of wheat depended very much on the N-min. content in the soil to 0–60 cm depth. The optimum nitrogen quantity from soil and fertilizers was 207 kg N-min. (turning point of function) + 40 kg ha-1 dose.