THE USE OF FERTILIZER AND SOIL-NITROGEN B Y SPRING BARLEY

In the years 1990 to 1992 the effect of nitrogen fertilization (rates of 0, 170, 255 and 340 mg N per pot, i.e. 0, 60, 90 and 120 kg N.ha(-1 )) and soil fertility on the yield of spring barley, Jaspis variety, w as studied in small-plot field trials in cylindrical pots without bott om recessed in soil profile, where a main criterion was the grain size structure and humus content (< 1%, 2% and > 3.5%). Moreover, nitrogen uptake from soil and fertilizer by spring barley was investigated usi ng stable isotope N-15 and the balance of fertilizer nitrogen on soils of various fertility was determined. Agrochemical characteristics and grain size structure of soils investigated in the trial are presented in Tab. I. It Follows from the results that the number of stems and s pikes in spring barley grows with gradated rates of nitrogen fertiliza tion and higher soil fertility (Figs 1 and 2). Regarding the grain and straw yields of spring barley, the most efficient in most soils is a rate of 60 kg N.ha(-1). Statistically significantly efficient are rate s 90 and 120 kg N.ha(-1) on soils 3 and 4 (with medium humus content). The yield of spring barley is affected by soil fertility in a decisiv e degree (Figs 3 and 4). The total nitrogen uptake by spring barley in creases with increasing soil fertility, on the other hand, nitrogen up take from fertilizer depends more on fertilizer rate than on soil prop erties. The share of soil nitrogen in the total uptake by the harvest of spring barley ranges from 92 to 78% and is practically identical in all studied soils. With growing rates of nitrogen fertilization the s hare of soil nitrogen decreases. Nitrogen fertilization leads to incre ased uptake of soil nitrogen by plants. This so-called ''priming effec t'' raises with increase of nitrogen fertilizers (Tab. II). The balanc e of fertilizer nitrogen in soils is in Tab. III; 26 to 34% of fertili zer nitrogen remains bound in soils studied by us. The value of the re st is not affected by soil properties. The use of nitrogen from fertil izer by spring barley is higher in soils with high humus content compa red with the soils of low humus content.