Botanical and production changes of permanent grassland after cessation ofmineral fertilization

Influence of mineral fertilization and its cessation on botanical and produ ctional changes were investigated on permanent grassland of Lolio-Cynosuret um cristati R. Tx. 1937 association during the years 1986 to 1996. Original ly motley grassland (73% monocotyledonous and 27% dicotyledonous species) h as changed to grassland (variants 4 and 5) with 73 to 84% portion of grasse s (Tab. IV) by increasing rates of N (series A) during eight years of ferti lization. PK fertilization (variant 2) supported the development of dicolyt edonous species (legumes and other meadow herbs) and reduced grass portion at the same time. After this period botanical composition in variant 3 (60 kg N.ha(-1)) was similar to the situation in the first year of fertilizatio n. Alternating application of N (series B) increased the dominance of legum es in the variants 6 and 7, but on contrary the higher rate of N applied il l the variants 8, 9 and 10 rose the portion of grass species. After three y ears cessation of mineral fertilization (Tab. V), unfertilized grasslands w ere characterized by nearly 50% portion of dicotyledonous species, more com petitive grass species (Festuca pratensis, Festuca rubra) reduction and mos ses widening in the stand (20%). Portion of legumes decreased expressively (by 24%) in the variant which was fertilized with PK fertilizers before ces sation (variant 2), while the dominance of other meadow herbs and grasses i ncreased. Occurrence of grasses was reduced by 12% in variants 3 and 4 and presence of legumes and other meadow herbs decreased in the same variants. Cessation of fertilizing minimally influenced variant treated with 240 kg N .ha(-1) (variant 5) although the covet was thinned out by grass and other h erbs dominance reduction (by 8 and 3.5%, resp.). The similar changes of bot anical composition than in the variants of series A were also registered in the variants of series B which were treated by periodically alternating N fertilization (variants 6 to 10). The higher the rates of N had been applie d before cessation of fertilization, the deeper the changes became after ce ssation. The portion of glasses, legumes but also other meadow herbs decrea sed and this caused thinning of the covers. Absence of fertilization also i nfluenced dry matter production especially in the second and third year aft er cessation (Tab. VI). Specific results of dry matter production were achi eved in the first year of fertilizing cessation when the yields were higher in comparison with the year 1993. However, fierce dry matter yields reduct ion ranging from 40 to 72% comparing to the year 1995, was registered in 19 96. It is obvious from the up to now achieved results that cessation of min eral fertilizing evokes a lot of changes in the permanent grassland. After three years absence of their application the floristical composition has ch anged expressively, influencing also both the production and the distributi on of dry matter in the cover.