THE EFFECT OF SITE AND WAY OF MANAGEMENT ON THE CONTENT OF MINERAL AND MINERALIZABLE NITROGEN IN SOILS

The content of mineral and mineralizable N. in soils (predominantly lo am chernozems) in three sites of the beet-growing regions: Sedlec, Suc hdol and Dobra Voda (380, 280, 265 m above sea level) at different fer tilization in spring and autumn was investigated. Treatments of fertil ization applied in exact field stationary experiments in sites Sedlec and Suchdol are presented in Tab. II. In 1994 winter wheat was cultiva ted in Sedlec and in 1995 haylage oat. The crop relation, manure and l ime application in the site Dobra Voda is in Tab. In, Crop rotation is executed regularly in Sedlec with 25% representation of alfalfa, 25% sugar beet and maize and 50% cereals. Since 1990 in Suchdol only cerea ls has been cultivated and more than 10 years neither fertilizers were applied, nor fabaceous crops were cultivated. In Dobra Voda sugar bee t, cabbage and cereals are cultivated at free crop rotation. Soil samp les were taken from a layer 0 to 25 cm and 25 to 50 cm in autumn (afte r harvest of a forecrop) and in spring. The soil was dried at 40 degre es C, homogenized and analyses were carried out from fine earth. To de termine mineralizable N, aerobic incubation method was used. Soil mixe d with sand (1 : 1) was seven days incubated at a moisture of 60% maxi mum water capacity and temperature 30 degrees C, then followed by dete rmination of mineral N in extract 1M KCI to 1993 by distillation and f rom 1994 colorimetrically on automatic analyzer SKALAR. Mineral N is t he content of mineral N before incubation and mineralizable N means a gain of mineral N during incubation. Results of analyses are given in ppm N. The content of mineral and mineralizable N exhibited relatively stable values in different sites. Lower values of mineral and mineral izable N were found in Suchdol (in total mostly 30 to 50 ppm N) where fertilizers were not applied long time and only cereals were cultivate d. The sites Sedlec and Dobra Voda showed higher values (as much as 80 ppm N in topsoil and about 60 ppm N in subsoil). A marked growth, par ticularly of mineralizable N, is after manuring together with mineral fertilization and after pea (Fig. 3). The effect of weather is apparen t, above all of precipitation (its amount and distribution). Significa nt to highly significant correlation was found in the site Sedlec betw een the grain yield of barley as well as N withdrawal and content of i nvestigated forms of N in soil. Higher correlation is in spring soil s ampling, in mineralizable N, sums of mineral and mineralizable N and i n the whole profile 0 to 50 cm.