EFFECT OF INTERACTION OF PLANT NUMBER X FERTILIZATION ON BIOMASS PRODUCTION, GRAIN-YIELD AND HARVEST INDEX IN MAIZE (ZEA-MAYS L) IN DIFFERENT YEARS

In a 3x4x2 factorial long-term trial on forest-residual chernozem soil, the independent and interactive effects of plant number, fertilization and genotype were studied on maize production (biomass, grain yield) and HI during 1989-1991 by three factor variance analysis. Every year the main effect of fertilization and plant number was significant at P=0,1%, and P=1% level on the biomass produciton, grain yield and HI of maize. The hybrid effect on biomass production and grain yield varied, but it proved to be each year significant on HI. From the significant interactions the most important was the one between fertilization and plant number. The biomass production at 235 kg ha-1 NPK dose increased in favourable years (1989, 1991) uptil maximum plant number (120 10(3) number ha-1), but without fertilization (N0P0K0) it did not increase over 60 10(3) number ha-1. At over-fertilization (N300P144K261) the maximum of biomass produciton was lower, and it occurred already with lower plant number. The highest grain yield was achieved each year at N100P48K87 fertilizer level, but the yield-increasing effect of higher plant number changed from year to year. As an effect of over-fertilization (E fertilizer level) the grain yield decreased at every plant number as compared to optimum fertilization. The yield reduction was especially large in the dry 1990. An increase in plant number resulted in consistent reduction of HI value (on the average from 47,07 to 36,21), on the other hand the HI value was the highest on C fertilization level and at over-fertilization (E fertilization level) was less than the of the unfertilized control (A fertilization level). There was a significant difference between the HI values of the two hybrids (NK PX 9283 (370) SC and Pioneer 3732 (450) SC).