Effect of graded and split spring nitrogen dressing and forecrop on winter wheat (Triticum aestivum L.) grain yield and its quality

The aim of the research was to obtain basis for improvement of winter wheat (variety Astella) spring nitrogen dressing optimization. For that purpose a three-year polyfactorial small-plot trial with six treatments of mineral fertilization and three forecrops (grain pea, maize for silage and spring barley) was established in 1998, in which the effect of graded single-use (five treatments) and split (one treatment) spring nitrogen dressing on grain yield and its baking quality was quantified. The trial was located in maize growing zone (site Borovce near Piestany, western part of Slovakia) on medium texture high productive Luvi-haplic Chernozem on loess in hot and very dry climatic region with average air daily temperature per year and vegetation season (April to September) 9.2 and 15.5 deg C and rainfalls totals 593 and 358 mm, respectively. Prior to sowing rate of phosphorus (19 % superphosphate) and potassium (50 % potash salt) applied under deep plough and nitrogen (46 % urea) applied at presowing cultivation of soil were determined according to their contents in soil at depth 0 to 0.3 m and for grain yield level 7 t/ha. In spring the winter wheat was dressed by nitrogen (27% calcium ammonium nitrate). Thee rate of regeneration nitrogen dressing at DC-21 was determined according to inorganic nitrogen content in soil depth 0 to 0.3 m and production and qualitative nitrogen dressing at DC-31 and DC-43 was determined according to dry matter weight of 100 plants and nitrogen content of shoots, respectively. At full ripeness stage (DC-92) grain yield, grain crude protein content (nitrogen content in dry matter x 5.70), grain wet gluten content, sedimentation index of flour according to Zeleny and Hagberg falling number of meal were determined. The results were evaluated by means of multifactor analysis of variance and correlation analysis. It follows from the results that grain yield was influenced by years (weather) and their interactions with the forecrops highly significantly and by spring nitrogen dressing itself significantly. The effect of the spring nitrogen dressing was differentiated according to weather of the years as well as by timing and dosing of nitrogen. In the year 2001 with high yield (on average for treatments 8.6 t/ha) in treatment N120/160 the grain yield was decreased and in treatment Nm was not changed in comparison with unfertilized treatment N0. In the less yielding years 1999 and 2000 gradual increase of nitrogen dressing rate increased the grain yield by 9.2 to 18.2 % and for treatment Nm by 19.1 % as compared with N0. Split of nitrogen dressing rate itself in treatment Nm increased grain yield in comparison with equal single-use rate of nitrogen dressing by 4.5 % on average from all years and by 5.7 % in two less yielding years. Sums of spring nitrogen dressing actually applied in treatment Nm after grain pea, maize for silage and spring barley were 51.7 - 55.0 - 60.0 kg N/ha, respectively. The levels of wheat grain baking characteristics (crude protein, sedimentation index, and falling number) were dominantly influenced by years (weather) and of wet gluten content by nitrogen dressing itself. By single-use nitrogen dressing at tillering (growth stage DC-21) equal and higher than 90 kg N/ha and also by split nitrogen dressing strong increase of crude protein and wet gluten content and mild increase of falling number is obtainable. From the viewpoint of quantity and quality of grain yield split nitrogen dressing was more effective than single-use fixedly chosen nitrogen rate dressing at tillering stage.