EFFECT OF MONOCROPPING ON MAIZE YIELD ON MEADOW SOIL IN LONG-TERM FERTILIZATION EXPERIMENTS

The yield changes' of maize produced in crop-rotation and monoculture were studied on the basis of data collected from filed experiments on meadow soil. The experiments are part of the National Long-Term Fertil ization Experiment started in 1966. Applied crop-rotations in the expe riment: a) triculture: pea - wheat - maize - maize; b) biculture: whea t - maize - wheat; c) monoculture: since 1966. The soil characteristic s of the experiments are: difficult tillage, slow mineralization of N in the springtime and considerable absorption of P, K. The study cover s the period between 1982-1993. I present the amounts of the yearly pr ecipitation (Table 1.) and precipitation fallen in the vegetation peri od of maize compared to the average. Heavy drought occurred in 1982-83 -86-90-93. During the examined 12 years the precipitation was 1600.7 m m less than the 50-years average. Because of the global warming half o f the examined years were droughty. Maize can tolerate the partial mon oculture considerably well, but after 10-15 years of monocropping the yield decreases by 1-3 t/ha in droughty years compared to the yields a chieved in crop rotation. Monocultural maize yields decreased signific anty in 1983,'90,'99,'93. The best forecrop for maize was the wheat. T he forecrop influences the requierement for fertilizer. The best yield s were obtained as follows: after wheat in triculture (pea-wheat-maize ) with a dose of 50-60 kg/ha N, in biculture (wheat-maize) with a dose of 60-80 kg/ha N, after maize in biculture with a dose of 80-100 kg/h a N, and in monoculture with a dose of 100-120 kg/ha N. In monoculture cropping the number of bacteria in the soil decreased significantly. The number of bacteria in 1 g soil was 59 million after wheat, 285 mil lion after maize, and only 16 million in monoculture cropping, which c an effect the soil life considerably. In monoculture cropping the Zn c ontent of the grain decreased by 4-5 mg/kg which can limit the yield o r cause losses in nutritive value. The yield decrease of monocultural maize can be explained by the impoverishment of the soil water supply. Thus the monocropping of maize, particularly in areas with poor rainf all, must be placed into crop-rotation after 10-15 years of monocultur e. The risk of monocropping should be decreased by using partial monoc ulture, a hybrid with good adaptability, 5-10 thousand less plant dens ity per hectare and irrigation if the conditions are given.