MINERAL AND MINERALIZABLE SOIL-NITROGEN A ND YIELDS OF CEREALS

At two sites Lipa and Svitavy in the potato-growing region (505 and 45 0 m above sea level) in long-term fertilizer stationary trial since 19 91 the content of mineral and mineralizable N was studied in autumn an d spring. Fertilized treatments are present in Tab. II. Soil samples w ere taken from a layer of 0 to 30 cm. Soil was dried at 40 degrees C, homogenized and analyses were performed from fine earth (2 mm). To det ermine mineralizable N, aerobic incubation method was used. Soil was s and-diluted (1 : 1), incubated for seven days at the moisture 60% MWC (maximum water holding capacity) and 30 degrees C, followed then by de termination of mineral N in extract 1M KCl by a colorimetric procedure on automated analyzer SKALAR. Mineral N represents the content of min eral N prior to incubation and mineralizable N represents an increment on mineral N during incubation. The results of analyses are present i n ppm N. The results of experimental years 1994 and 1995 (the experime ntal crop was in 1994 winter wheat and in 1995 spring barley) indicate that the highest values of mineral and mineralizable N were found in the autumn of 1993 after harvest of potatoes (before sowing of wheat) in treatments which were manure-fertilized in autumn of 1992 and ferti lizers were then applied. In 1994 a marked decrease in investigated va lues occurred and as late as in spring period of 1995 an increase in m ineral and mineralizable N was again recorded. At the site Lipa mostly higher content of mineral N was found. An absence of liming caused re duction in the content of mineral and mineralizable N, as well as the yield of grain, particularly in barley at the site Svitavy. A good cor relation was found between the content of N in soil, yield of grain an d N intake by harvest. Greater closeness of relationships is at Lipa, particularly in wheat in the autumn, on the contrary, in barley in the spring season.